| Message ID | 20190626192234.11725-16-casey@schaufler-ca.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | LSM: Module stacking for AppArmor | expand |
On Wed, Jun 26, 2019 at 12:22:26PM -0700, Casey Schaufler wrote: > Create a new entry "display" in /proc/.../attr for controlling > which LSM security information is displayed for a process. > The name of an active LSM that supplies hooks for human readable > data may be written to "display" to set the value. The name of > the LSM currently in use can be read from "display". > At this point there can only be one LSM capable of display > active. > > Signed-off-by: Casey Schaufler <casey@schaufler-ca.com> Reviewed-by: Kees Cook <keescook@chromium.org> -Kees > --- > fs/proc/base.c | 1 + > security/security.c | 129 ++++++++++++++++++++++++++++++++++++++------ > 2 files changed, 113 insertions(+), 17 deletions(-) > > diff --git a/fs/proc/base.c b/fs/proc/base.c > index ddef482f1334..7bf70e041315 100644 > --- a/fs/proc/base.c > +++ b/fs/proc/base.c > @@ -2618,6 +2618,7 @@ static const struct pid_entry attr_dir_stuff[] = { > ATTR(NULL, "fscreate", 0666), > ATTR(NULL, "keycreate", 0666), > ATTR(NULL, "sockcreate", 0666), > + ATTR(NULL, "display", 0666), > #ifdef CONFIG_SECURITY_SMACK > DIR("smack", 0555, > proc_smack_attr_dir_inode_ops, proc_smack_attr_dir_ops), > diff --git a/security/security.c b/security/security.c > index 3180a6f30625..82e29c477fa4 100644 > --- a/security/security.c > +++ b/security/security.c > @@ -46,7 +46,9 @@ static struct kmem_cache *lsm_file_cache; > static struct kmem_cache *lsm_inode_cache; > > char *lsm_names; > -static struct lsm_blob_sizes blob_sizes __lsm_ro_after_init; > +static struct lsm_blob_sizes blob_sizes __lsm_ro_after_init = { > + .lbs_task = sizeof(int), /* slot number for the "display" LSM */ > +}; > > /* Boot-time LSM user choice */ > static __initdata const char *chosen_lsm_order; > @@ -423,8 +425,10 @@ static int lsm_append(const char *new, char **result) > > /* > * Current index to use while initializing the lsmblob secid list. > + * Pointers to the LSM id structures for local use. > */ > static int lsm_slot; > +static struct lsm_id *lsm_slotlist[LSMBLOB_ENTRIES]; > > /** > * security_add_hooks - Add a modules hooks to the hook lists. > @@ -444,6 +448,7 @@ void __init security_add_hooks(struct security_hook_list *hooks, int count, > if (lsmid->slot == LSMBLOB_NEEDED) { > if (lsm_slot >= LSMBLOB_ENTRIES) > panic("%s Too many LSMs registered.\n", __func__); > + lsm_slotlist[lsm_slot] = lsmid; > lsmid->slot = lsm_slot++; > init_debug("%s assigned lsmblob slot %d\n", lsmid->lsm, > lsmid->slot); > @@ -564,6 +569,8 @@ int lsm_inode_alloc(struct inode *inode) > */ > static int lsm_task_alloc(struct task_struct *task) > { > + int *display; > + > if (blob_sizes.lbs_task == 0) { > task->security = NULL; > return 0; > @@ -572,6 +579,15 @@ static int lsm_task_alloc(struct task_struct *task) > task->security = kzalloc(blob_sizes.lbs_task, GFP_KERNEL); > if (task->security == NULL) > return -ENOMEM; > + > + /* > + * The start of the task blob contains the "display" LSM slot number. > + * Start with it set to the invalid slot number, indicating that the > + * default first registered LSM be displayed. > + */ > + display = task->security; > + *display = LSMBLOB_INVALID; > + > return 0; > } > > @@ -1563,14 +1579,24 @@ int security_file_open(struct file *file) > > int security_task_alloc(struct task_struct *task, unsigned long clone_flags) > { > + int *odisplay = current->security; > + int *ndisplay; > int rc = lsm_task_alloc(task); > > - if (rc) > + if (unlikely(rc)) > return rc; > + > rc = call_int_hook(task_alloc, 0, task, clone_flags); > - if (unlikely(rc)) > + if (unlikely(rc)) { > security_task_free(task); > - return rc; > + return rc; > + } > + > + ndisplay = task->security; > + if (ndisplay && odisplay) > + *ndisplay = *odisplay; > + > + return 0; > } > > void security_task_free(struct task_struct *task) > @@ -1967,10 +1993,29 @@ int security_getprocattr(struct task_struct *p, const char *lsm, char *name, > char **value) > { > struct security_hook_list *hp; > + int *display = current->security; > + int slot = 0; > + > + if (!strcmp(name, "display")) { > + /* > + * lsm_slot will be 0 if there are no displaying modules. > + */ > + if (lsm_slot == 0) > + return -EINVAL; > + if (*display != LSMBLOB_INVALID) > + slot = *display; > + *value = kstrdup(lsm_slotlist[slot]->lsm, GFP_KERNEL); > + if (*value) > + return strlen(*value); > + return -ENOMEM; > + } > > hlist_for_each_entry(hp, &security_hook_heads.getprocattr, list) { > if (lsm != NULL && strcmp(lsm, hp->lsmid->lsm)) > continue; > + if (lsm == NULL && *display != LSMBLOB_INVALID && > + *display != hp->lsmid->slot) > + continue; > return hp->hook.getprocattr(p, name, value); > } > return -EINVAL; > @@ -1980,10 +2025,46 @@ int security_setprocattr(const char *lsm, const char *name, void *value, > size_t size) > { > struct security_hook_list *hp; > + char *term; > + char *cp; > + int *display = current->security; > + int rc = -EINVAL; > + int slot = 0; > + > + if (!strcmp(name, "display")) { > + /* > + * lsm_slot will be 0 if there are no displaying modules. > + */ > + if (lsm_slot == 0 || size == 0) > + return -EINVAL; > + cp = kzalloc(size + 1, GFP_KERNEL); > + if (cp == NULL) > + return -ENOMEM; > + memcpy(cp, value, size); > + > + term = strchr(cp, ' '); > + if (term == NULL) > + term = strchr(cp, '\n'); > + if (term != NULL) > + *term = '\0'; > + > + for (slot = 0; slot < lsm_slot; slot++) > + if (!strcmp(cp, lsm_slotlist[slot]->lsm)) { > + *display = lsm_slotlist[slot]->slot; > + rc = size; > + break; > + } > + > + kfree(cp); > + return rc; > + } > > hlist_for_each_entry(hp, &security_hook_heads.setprocattr, list) { > if (lsm != NULL && strcmp(lsm, hp->lsmid->lsm)) > continue; > + if (lsm == NULL && *display != LSMBLOB_INVALID && > + *display != hp->lsmid->slot) > + continue; > return hp->hook.setprocattr(name, value, size); > } > return -EINVAL; > @@ -2003,15 +2084,15 @@ EXPORT_SYMBOL(security_ismaclabel); > int security_secid_to_secctx(struct lsmblob *blob, char **secdata, u32 *seclen) > { > struct security_hook_list *hp; > - int rc; > + int *display = current->security; > > hlist_for_each_entry(hp, &security_hook_heads.secid_to_secctx, list) { > if (WARN_ON(hp->lsmid->slot < 0 || hp->lsmid->slot >= lsm_slot)) > continue; > - rc = hp->hook.secid_to_secctx(blob->secid[hp->lsmid->slot], > - secdata, seclen); > - if (rc != 0) > - return rc; > + if (*display == LSMBLOB_INVALID || *display == hp->lsmid->slot) > + return hp->hook.secid_to_secctx( > + blob->secid[hp->lsmid->slot], > + secdata, seclen); > } > return 0; > } > @@ -2021,16 +2102,15 @@ int security_secctx_to_secid(const char *secdata, u32 seclen, > struct lsmblob *blob) > { > struct security_hook_list *hp; > - int rc; > + int *display = current->security; > > lsmblob_init(blob, 0); > hlist_for_each_entry(hp, &security_hook_heads.secctx_to_secid, list) { > if (WARN_ON(hp->lsmid->slot < 0 || hp->lsmid->slot >= lsm_slot)) > continue; > - rc = hp->hook.secctx_to_secid(secdata, seclen, > - &blob->secid[hp->lsmid->slot]); > - if (rc != 0) > - return rc; > + if (*display == LSMBLOB_INVALID || *display == hp->lsmid->slot) > + return hp->hook.secctx_to_secid(secdata, seclen, > + &blob->secid[hp->lsmid->slot]); > } > return 0; > } > @@ -2038,7 +2118,15 @@ EXPORT_SYMBOL(security_secctx_to_secid); > > void security_release_secctx(char *secdata, u32 seclen) > { > - call_void_hook(release_secctx, secdata, seclen); > + struct security_hook_list *hp; > + int *display = current->security; > + > + hlist_for_each_entry(hp, &security_hook_heads.release_secctx, list) > + if (*display == LSMBLOB_INVALID || > + *display == hp->lsmid->slot) { > + hp->hook.release_secctx(secdata, seclen); > + return; > + } > } > EXPORT_SYMBOL(security_release_secctx); > > @@ -2163,8 +2251,15 @@ EXPORT_SYMBOL(security_sock_rcv_skb); > int security_socket_getpeersec_stream(struct socket *sock, char __user *optval, > int __user *optlen, unsigned len) > { > - return call_int_hook(socket_getpeersec_stream, -ENOPROTOOPT, sock, > - optval, optlen, len); > + int *display = current->security; > + struct security_hook_list *hp; > + > + hlist_for_each_entry(hp, &security_hook_heads.socket_getpeersec_stream, > + list) > + if (*display == LSMBLOB_INVALID || *display == hp->lsmid->slot) > + return hp->hook.socket_getpeersec_stream(sock, optval, > + optlen, len); > + return -ENOPROTOOPT; > } > > int security_socket_getpeersec_dgram(struct socket *sock, struct sk_buff *skb, > -- > 2.20.1 >
On 6/26/19 12:22 PM, Casey Schaufler wrote: > Create a new entry "display" in /proc/.../attr for controlling > which LSM security information is displayed for a process. > The name of an active LSM that supplies hooks for human readable > data may be written to "display" to set the value. The name of > the LSM currently in use can be read from "display". > At this point there can only be one LSM capable of display > active. > > Signed-off-by: Casey Schaufler <casey@schaufler-ca.com> Reviewed-by: John Johansen <john.johansen@canonical.com> > --- > fs/proc/base.c | 1 + > security/security.c | 129 ++++++++++++++++++++++++++++++++++++++------ > 2 files changed, 113 insertions(+), 17 deletions(-) > > diff --git a/fs/proc/base.c b/fs/proc/base.c > index ddef482f1334..7bf70e041315 100644 > --- a/fs/proc/base.c > +++ b/fs/proc/base.c > @@ -2618,6 +2618,7 @@ static const struct pid_entry attr_dir_stuff[] = { > ATTR(NULL, "fscreate", 0666), > ATTR(NULL, "keycreate", 0666), > ATTR(NULL, "sockcreate", 0666), > + ATTR(NULL, "display", 0666), > #ifdef CONFIG_SECURITY_SMACK > DIR("smack", 0555, > proc_smack_attr_dir_inode_ops, proc_smack_attr_dir_ops), > diff --git a/security/security.c b/security/security.c > index 3180a6f30625..82e29c477fa4 100644 > --- a/security/security.c > +++ b/security/security.c > @@ -46,7 +46,9 @@ static struct kmem_cache *lsm_file_cache; > static struct kmem_cache *lsm_inode_cache; > > char *lsm_names; > -static struct lsm_blob_sizes blob_sizes __lsm_ro_after_init; > +static struct lsm_blob_sizes blob_sizes __lsm_ro_after_init = { > + .lbs_task = sizeof(int), /* slot number for the "display" LSM */ > +}; > > /* Boot-time LSM user choice */ > static __initdata const char *chosen_lsm_order; > @@ -423,8 +425,10 @@ static int lsm_append(const char *new, char **result) > > /* > * Current index to use while initializing the lsmblob secid list. > + * Pointers to the LSM id structures for local use. > */ > static int lsm_slot; > +static struct lsm_id *lsm_slotlist[LSMBLOB_ENTRIES]; > > /** > * security_add_hooks - Add a modules hooks to the hook lists. > @@ -444,6 +448,7 @@ void __init security_add_hooks(struct security_hook_list *hooks, int count, > if (lsmid->slot == LSMBLOB_NEEDED) { > if (lsm_slot >= LSMBLOB_ENTRIES) > panic("%s Too many LSMs registered.\n", __func__); > + lsm_slotlist[lsm_slot] = lsmid; > lsmid->slot = lsm_slot++; > init_debug("%s assigned lsmblob slot %d\n", lsmid->lsm, > lsmid->slot); > @@ -564,6 +569,8 @@ int lsm_inode_alloc(struct inode *inode) > */ > static int lsm_task_alloc(struct task_struct *task) > { > + int *display; > + > if (blob_sizes.lbs_task == 0) { > task->security = NULL; > return 0; > @@ -572,6 +579,15 @@ static int lsm_task_alloc(struct task_struct *task) > task->security = kzalloc(blob_sizes.lbs_task, GFP_KERNEL); > if (task->security == NULL) > return -ENOMEM; > + > + /* > + * The start of the task blob contains the "display" LSM slot number. > + * Start with it set to the invalid slot number, indicating that the > + * default first registered LSM be displayed. > + */ > + display = task->security; > + *display = LSMBLOB_INVALID; > + > return 0; > } > > @@ -1563,14 +1579,24 @@ int security_file_open(struct file *file) > > int security_task_alloc(struct task_struct *task, unsigned long clone_flags) > { > + int *odisplay = current->security; > + int *ndisplay; > int rc = lsm_task_alloc(task); > > - if (rc) > + if (unlikely(rc)) > return rc; > + > rc = call_int_hook(task_alloc, 0, task, clone_flags); > - if (unlikely(rc)) > + if (unlikely(rc)) { > security_task_free(task); > - return rc; > + return rc; > + } > + > + ndisplay = task->security; > + if (ndisplay && odisplay) > + *ndisplay = *odisplay; > + > + return 0; > } > > void security_task_free(struct task_struct *task) > @@ -1967,10 +1993,29 @@ int security_getprocattr(struct task_struct *p, const char *lsm, char *name, > char **value) > { > struct security_hook_list *hp; > + int *display = current->security; > + int slot = 0; > + > + if (!strcmp(name, "display")) { > + /* > + * lsm_slot will be 0 if there are no displaying modules. > + */ > + if (lsm_slot == 0) > + return -EINVAL; > + if (*display != LSMBLOB_INVALID) > + slot = *display; > + *value = kstrdup(lsm_slotlist[slot]->lsm, GFP_KERNEL); > + if (*value) > + return strlen(*value); > + return -ENOMEM; > + } > > hlist_for_each_entry(hp, &security_hook_heads.getprocattr, list) { > if (lsm != NULL && strcmp(lsm, hp->lsmid->lsm)) > continue; > + if (lsm == NULL && *display != LSMBLOB_INVALID && > + *display != hp->lsmid->slot) > + continue; > return hp->hook.getprocattr(p, name, value); > } > return -EINVAL; > @@ -1980,10 +2025,46 @@ int security_setprocattr(const char *lsm, const char *name, void *value, > size_t size) > { > struct security_hook_list *hp; > + char *term; > + char *cp; > + int *display = current->security; > + int rc = -EINVAL; > + int slot = 0; > + > + if (!strcmp(name, "display")) { > + /* > + * lsm_slot will be 0 if there are no displaying modules. > + */ > + if (lsm_slot == 0 || size == 0) > + return -EINVAL; > + cp = kzalloc(size + 1, GFP_KERNEL); > + if (cp == NULL) > + return -ENOMEM; > + memcpy(cp, value, size); > + > + term = strchr(cp, ' '); > + if (term == NULL) > + term = strchr(cp, '\n'); > + if (term != NULL) > + *term = '\0'; > + > + for (slot = 0; slot < lsm_slot; slot++) > + if (!strcmp(cp, lsm_slotlist[slot]->lsm)) { > + *display = lsm_slotlist[slot]->slot; > + rc = size; > + break; > + } > + > + kfree(cp); > + return rc; > + } > > hlist_for_each_entry(hp, &security_hook_heads.setprocattr, list) { > if (lsm != NULL && strcmp(lsm, hp->lsmid->lsm)) > continue; > + if (lsm == NULL && *display != LSMBLOB_INVALID && > + *display != hp->lsmid->slot) > + continue; > return hp->hook.setprocattr(name, value, size); > } > return -EINVAL; > @@ -2003,15 +2084,15 @@ EXPORT_SYMBOL(security_ismaclabel); > int security_secid_to_secctx(struct lsmblob *blob, char **secdata, u32 *seclen) > { > struct security_hook_list *hp; > - int rc; > + int *display = current->security; > > hlist_for_each_entry(hp, &security_hook_heads.secid_to_secctx, list) { > if (WARN_ON(hp->lsmid->slot < 0 || hp->lsmid->slot >= lsm_slot)) > continue; > - rc = hp->hook.secid_to_secctx(blob->secid[hp->lsmid->slot], > - secdata, seclen); > - if (rc != 0) > - return rc; > + if (*display == LSMBLOB_INVALID || *display == hp->lsmid->slot) > + return hp->hook.secid_to_secctx( > + blob->secid[hp->lsmid->slot], > + secdata, seclen); > } > return 0; > } > @@ -2021,16 +2102,15 @@ int security_secctx_to_secid(const char *secdata, u32 seclen, > struct lsmblob *blob) > { > struct security_hook_list *hp; > - int rc; > + int *display = current->security; > > lsmblob_init(blob, 0); > hlist_for_each_entry(hp, &security_hook_heads.secctx_to_secid, list) { > if (WARN_ON(hp->lsmid->slot < 0 || hp->lsmid->slot >= lsm_slot)) > continue; > - rc = hp->hook.secctx_to_secid(secdata, seclen, > - &blob->secid[hp->lsmid->slot]); > - if (rc != 0) > - return rc; > + if (*display == LSMBLOB_INVALID || *display == hp->lsmid->slot) > + return hp->hook.secctx_to_secid(secdata, seclen, > + &blob->secid[hp->lsmid->slot]); > } > return 0; > } > @@ -2038,7 +2118,15 @@ EXPORT_SYMBOL(security_secctx_to_secid); > > void security_release_secctx(char *secdata, u32 seclen) > { > - call_void_hook(release_secctx, secdata, seclen); > + struct security_hook_list *hp; > + int *display = current->security; > + > + hlist_for_each_entry(hp, &security_hook_heads.release_secctx, list) > + if (*display == LSMBLOB_INVALID || > + *display == hp->lsmid->slot) { > + hp->hook.release_secctx(secdata, seclen); > + return; > + } > } > EXPORT_SYMBOL(security_release_secctx); > > @@ -2163,8 +2251,15 @@ EXPORT_SYMBOL(security_sock_rcv_skb); > int security_socket_getpeersec_stream(struct socket *sock, char __user *optval, > int __user *optlen, unsigned len) > { > - return call_int_hook(socket_getpeersec_stream, -ENOPROTOOPT, sock, > - optval, optlen, len); > + int *display = current->security; > + struct security_hook_list *hp; > + > + hlist_for_each_entry(hp, &security_hook_heads.socket_getpeersec_stream, > + list) > + if (*display == LSMBLOB_INVALID || *display == hp->lsmid->slot) > + return hp->hook.socket_getpeersec_stream(sock, optval, > + optlen, len); > + return -ENOPROTOOPT; > } > > int security_socket_getpeersec_dgram(struct socket *sock, struct sk_buff *skb, >
On 6/26/19 3:22 PM, Casey Schaufler wrote: > Create a new entry "display" in /proc/.../attr for controlling > which LSM security information is displayed for a process. > The name of an active LSM that supplies hooks for human readable > data may be written to "display" to set the value. The name of > the LSM currently in use can be read from "display". > At this point there can only be one LSM capable of display > active. IIUC, presently, at the end of the entire series, 1) Any process can change its display attribute to any enabled security module, and no security module can veto that change. 2) The display attribute is inherited across fork and exec, even execs that change credentials, and again no security module has control over the inheritance of this attribute. 3) Setting the display attribute affects more than just the contexts read or written by the process itself: - Contexts reported in audit logs, - Contexts passed across binder (generated in sender context, delivered to receiver), - Contexts passed to NFS servers for new files, - Contexts returned by NFS servers for existing files, - Netlink-related contexts (?possibly generated in sender context rather than receiver context?), - This list may not be complete. 4) A security_secid_to_secctx() in one process' context (e.g. sender) or with one display value followed later by a security_secctx_to_secid() call in a different process' context (e.g. receiver) or with a different display value may ask a different security module to perform the reverse translation of the context than the forward translation. Is that correct? If so, it seems problematic. > > Signed-off-by: Casey Schaufler <casey@schaufler-ca.com> > --- > fs/proc/base.c | 1 + > security/security.c | 129 ++++++++++++++++++++++++++++++++++++++------ > 2 files changed, 113 insertions(+), 17 deletions(-) > > diff --git a/fs/proc/base.c b/fs/proc/base.c > index ddef482f1334..7bf70e041315 100644 > --- a/fs/proc/base.c > +++ b/fs/proc/base.c > @@ -2618,6 +2618,7 @@ static const struct pid_entry attr_dir_stuff[] = { > ATTR(NULL, "fscreate", 0666), > ATTR(NULL, "keycreate", 0666), > ATTR(NULL, "sockcreate", 0666), > + ATTR(NULL, "display", 0666), > #ifdef CONFIG_SECURITY_SMACK > DIR("smack", 0555, > proc_smack_attr_dir_inode_ops, proc_smack_attr_dir_ops), > diff --git a/security/security.c b/security/security.c > index 3180a6f30625..82e29c477fa4 100644 > --- a/security/security.c > +++ b/security/security.c > @@ -46,7 +46,9 @@ static struct kmem_cache *lsm_file_cache; > static struct kmem_cache *lsm_inode_cache; > > char *lsm_names; > -static struct lsm_blob_sizes blob_sizes __lsm_ro_after_init; > +static struct lsm_blob_sizes blob_sizes __lsm_ro_after_init = { > + .lbs_task = sizeof(int), /* slot number for the "display" LSM */ > +}; > > /* Boot-time LSM user choice */ > static __initdata const char *chosen_lsm_order; > @@ -423,8 +425,10 @@ static int lsm_append(const char *new, char **result) > > /* > * Current index to use while initializing the lsmblob secid list. > + * Pointers to the LSM id structures for local use. > */ > static int lsm_slot; > +static struct lsm_id *lsm_slotlist[LSMBLOB_ENTRIES]; > > /** > * security_add_hooks - Add a modules hooks to the hook lists. > @@ -444,6 +448,7 @@ void __init security_add_hooks(struct security_hook_list *hooks, int count, > if (lsmid->slot == LSMBLOB_NEEDED) { > if (lsm_slot >= LSMBLOB_ENTRIES) > panic("%s Too many LSMs registered.\n", __func__); > + lsm_slotlist[lsm_slot] = lsmid; > lsmid->slot = lsm_slot++; > init_debug("%s assigned lsmblob slot %d\n", lsmid->lsm, > lsmid->slot); > @@ -564,6 +569,8 @@ int lsm_inode_alloc(struct inode *inode) > */ > static int lsm_task_alloc(struct task_struct *task) > { > + int *display; > + > if (blob_sizes.lbs_task == 0) { > task->security = NULL; > return 0; > @@ -572,6 +579,15 @@ static int lsm_task_alloc(struct task_struct *task) > task->security = kzalloc(blob_sizes.lbs_task, GFP_KERNEL); > if (task->security == NULL) > return -ENOMEM; > + > + /* > + * The start of the task blob contains the "display" LSM slot number. > + * Start with it set to the invalid slot number, indicating that the > + * default first registered LSM be displayed. > + */ > + display = task->security; > + *display = LSMBLOB_INVALID; > + > return 0; > } > > @@ -1563,14 +1579,24 @@ int security_file_open(struct file *file) > > int security_task_alloc(struct task_struct *task, unsigned long clone_flags) > { > + int *odisplay = current->security; > + int *ndisplay; > int rc = lsm_task_alloc(task); > > - if (rc) > + if (unlikely(rc)) > return rc; > + > rc = call_int_hook(task_alloc, 0, task, clone_flags); > - if (unlikely(rc)) > + if (unlikely(rc)) { > security_task_free(task); > - return rc; > + return rc; > + } > + > + ndisplay = task->security; > + if (ndisplay && odisplay) > + *ndisplay = *odisplay; > + > + return 0; > } > > void security_task_free(struct task_struct *task) > @@ -1967,10 +1993,29 @@ int security_getprocattr(struct task_struct *p, const char *lsm, char *name, > char **value) > { > struct security_hook_list *hp; > + int *display = current->security; > + int slot = 0; > + > + if (!strcmp(name, "display")) { > + /* > + * lsm_slot will be 0 if there are no displaying modules. > + */ > + if (lsm_slot == 0) > + return -EINVAL; > + if (*display != LSMBLOB_INVALID) > + slot = *display; > + *value = kstrdup(lsm_slotlist[slot]->lsm, GFP_KERNEL); > + if (*value) > + return strlen(*value); > + return -ENOMEM; > + } > > hlist_for_each_entry(hp, &security_hook_heads.getprocattr, list) { > if (lsm != NULL && strcmp(lsm, hp->lsmid->lsm)) > continue; > + if (lsm == NULL && *display != LSMBLOB_INVALID && > + *display != hp->lsmid->slot) > + continue; > return hp->hook.getprocattr(p, name, value); > } > return -EINVAL; > @@ -1980,10 +2025,46 @@ int security_setprocattr(const char *lsm, const char *name, void *value, > size_t size) > { > struct security_hook_list *hp; > + char *term; > + char *cp; > + int *display = current->security; > + int rc = -EINVAL; > + int slot = 0; > + > + if (!strcmp(name, "display")) { > + /* > + * lsm_slot will be 0 if there are no displaying modules. > + */ > + if (lsm_slot == 0 || size == 0) > + return -EINVAL; > + cp = kzalloc(size + 1, GFP_KERNEL); > + if (cp == NULL) > + return -ENOMEM; > + memcpy(cp, value, size); > + > + term = strchr(cp, ' '); > + if (term == NULL) > + term = strchr(cp, '\n'); > + if (term != NULL) > + *term = '\0'; > + > + for (slot = 0; slot < lsm_slot; slot++) > + if (!strcmp(cp, lsm_slotlist[slot]->lsm)) { > + *display = lsm_slotlist[slot]->slot; > + rc = size; > + break; > + } > + > + kfree(cp); > + return rc; > + } > > hlist_for_each_entry(hp, &security_hook_heads.setprocattr, list) { > if (lsm != NULL && strcmp(lsm, hp->lsmid->lsm)) > continue; > + if (lsm == NULL && *display != LSMBLOB_INVALID && > + *display != hp->lsmid->slot) > + continue; > return hp->hook.setprocattr(name, value, size); > } > return -EINVAL; > @@ -2003,15 +2084,15 @@ EXPORT_SYMBOL(security_ismaclabel); > int security_secid_to_secctx(struct lsmblob *blob, char **secdata, u32 *seclen) > { > struct security_hook_list *hp; > - int rc; > + int *display = current->security; > > hlist_for_each_entry(hp, &security_hook_heads.secid_to_secctx, list) { > if (WARN_ON(hp->lsmid->slot < 0 || hp->lsmid->slot >= lsm_slot)) > continue; > - rc = hp->hook.secid_to_secctx(blob->secid[hp->lsmid->slot], > - secdata, seclen); > - if (rc != 0) > - return rc; > + if (*display == LSMBLOB_INVALID || *display == hp->lsmid->slot) > + return hp->hook.secid_to_secctx( > + blob->secid[hp->lsmid->slot], > + secdata, seclen); > } > return 0; > } > @@ -2021,16 +2102,15 @@ int security_secctx_to_secid(const char *secdata, u32 seclen, > struct lsmblob *blob) > { > struct security_hook_list *hp; > - int rc; > + int *display = current->security; > > lsmblob_init(blob, 0); > hlist_for_each_entry(hp, &security_hook_heads.secctx_to_secid, list) { > if (WARN_ON(hp->lsmid->slot < 0 || hp->lsmid->slot >= lsm_slot)) > continue; > - rc = hp->hook.secctx_to_secid(secdata, seclen, > - &blob->secid[hp->lsmid->slot]); > - if (rc != 0) > - return rc; > + if (*display == LSMBLOB_INVALID || *display == hp->lsmid->slot) > + return hp->hook.secctx_to_secid(secdata, seclen, > + &blob->secid[hp->lsmid->slot]); > } > return 0; > } > @@ -2038,7 +2118,15 @@ EXPORT_SYMBOL(security_secctx_to_secid); > > void security_release_secctx(char *secdata, u32 seclen) > { > - call_void_hook(release_secctx, secdata, seclen); > + struct security_hook_list *hp; > + int *display = current->security; > + > + hlist_for_each_entry(hp, &security_hook_heads.release_secctx, list) > + if (*display == LSMBLOB_INVALID || > + *display == hp->lsmid->slot) { > + hp->hook.release_secctx(secdata, seclen); > + return; > + } > } > EXPORT_SYMBOL(security_release_secctx); > > @@ -2163,8 +2251,15 @@ EXPORT_SYMBOL(security_sock_rcv_skb); > int security_socket_getpeersec_stream(struct socket *sock, char __user *optval, > int __user *optlen, unsigned len) > { > - return call_int_hook(socket_getpeersec_stream, -ENOPROTOOPT, sock, > - optval, optlen, len); > + int *display = current->security; > + struct security_hook_list *hp; > + > + hlist_for_each_entry(hp, &security_hook_heads.socket_getpeersec_stream, > + list) > + if (*display == LSMBLOB_INVALID || *display == hp->lsmid->slot) > + return hp->hook.socket_getpeersec_stream(sock, optval, > + optlen, len); > + return -ENOPROTOOPT; > } > > int security_socket_getpeersec_dgram(struct socket *sock, struct sk_buff *skb, >
On 6/28/2019 7:45 AM, Stephen Smalley wrote: > On 6/26/19 3:22 PM, Casey Schaufler wrote: >> Create a new entry "display" in /proc/.../attr for controlling >> which LSM security information is displayed for a process. >> The name of an active LSM that supplies hooks for human readable >> data may be written to "display" to set the value. The name of >> the LSM currently in use can be read from "display". >> At this point there can only be one LSM capable of display >> active. > > IIUC, presently, at the end of the entire series, > > 1) Any process can change its display attribute to any enabled security module, and no security module can veto that change. That is correct. If a security module could hoard the display it could prevent user space from functioning in a multiple module environment. > 2) The display attribute is inherited across fork and exec, even execs that change credentials, and again no security module has control over the inheritance of this attribute. Also correct. Scripts don't work otherwise. > > 3) Setting the display attribute affects more than just the contexts read or written by the process itself: > - Contexts reported in audit logs, > - Contexts passed across binder (generated in sender context, delivered to receiver), > - Contexts passed to NFS servers for new files, > - Contexts returned by NFS servers for existing files, > - Netlink-related contexts (?possibly generated in sender context rather than receiver context?), > - This list may not be complete. Any of which can be changed should a more rational behavior be proposed. One possibility is to use lsm='value',lsm='value' encoding for internal communications, but there's been considerable resistance to anything like that. > 4) A security_secid_to_secctx() in one process' context (e.g. sender) or with one display value followed later by a security_secctx_to_secid() call in a different process' context (e.g. receiver) or with a different display value may ask a different security module to perform the reverse translation of the context than the forward translation. Do you have an example of where this might happen? Contexts are rarely used within the kernel. The usual behavior is to generate them, send them out to user space, and delete them. They get cached in some networking code, but not in cases where more than one (existing) security module will ever use them. Binder may be an exception, but only SELinux (currently) supports binder. > Is that correct? If so, it seems problematic. Balancing backward compatibility with new behavior is hard! What would you suggest for audit logs? Should we put all LSM data in every record? Is NFS a concern for anyone not using SELinux? There is no user space that uses display, and it's going to take some time to work out all the kinks before we even think about teaching systemd about it. > >> >> Signed-off-by: Casey Schaufler <casey@schaufler-ca.com> >> --- >> fs/proc/base.c | 1 + >> security/security.c | 129 ++++++++++++++++++++++++++++++++++++++------ >> 2 files changed, 113 insertions(+), 17 deletions(-) >> >> diff --git a/fs/proc/base.c b/fs/proc/base.c >> index ddef482f1334..7bf70e041315 100644 >> --- a/fs/proc/base.c >> +++ b/fs/proc/base.c >> @@ -2618,6 +2618,7 @@ static const struct pid_entry attr_dir_stuff[] = { >> ATTR(NULL, "fscreate", 0666), >> ATTR(NULL, "keycreate", 0666), >> ATTR(NULL, "sockcreate", 0666), >> + ATTR(NULL, "display", 0666), >> #ifdef CONFIG_SECURITY_SMACK >> DIR("smack", 0555, >> proc_smack_attr_dir_inode_ops, proc_smack_attr_dir_ops), >> diff --git a/security/security.c b/security/security.c >> index 3180a6f30625..82e29c477fa4 100644 >> --- a/security/security.c >> +++ b/security/security.c >> @@ -46,7 +46,9 @@ static struct kmem_cache *lsm_file_cache; >> static struct kmem_cache *lsm_inode_cache; >> char *lsm_names; >> -static struct lsm_blob_sizes blob_sizes __lsm_ro_after_init; >> +static struct lsm_blob_sizes blob_sizes __lsm_ro_after_init = { >> + .lbs_task = sizeof(int), /* slot number for the "display" LSM */ >> +}; >> /* Boot-time LSM user choice */ >> static __initdata const char *chosen_lsm_order; >> @@ -423,8 +425,10 @@ static int lsm_append(const char *new, char **result) >> /* >> * Current index to use while initializing the lsmblob secid list. >> + * Pointers to the LSM id structures for local use. >> */ >> static int lsm_slot; >> +static struct lsm_id *lsm_slotlist[LSMBLOB_ENTRIES]; >> /** >> * security_add_hooks - Add a modules hooks to the hook lists. >> @@ -444,6 +448,7 @@ void __init security_add_hooks(struct security_hook_list *hooks, int count, >> if (lsmid->slot == LSMBLOB_NEEDED) { >> if (lsm_slot >= LSMBLOB_ENTRIES) >> panic("%s Too many LSMs registered.\n", __func__); >> + lsm_slotlist[lsm_slot] = lsmid; >> lsmid->slot = lsm_slot++; >> init_debug("%s assigned lsmblob slot %d\n", lsmid->lsm, >> lsmid->slot); >> @@ -564,6 +569,8 @@ int lsm_inode_alloc(struct inode *inode) >> */ >> static int lsm_task_alloc(struct task_struct *task) >> { >> + int *display; >> + >> if (blob_sizes.lbs_task == 0) { >> task->security = NULL; >> return 0; >> @@ -572,6 +579,15 @@ static int lsm_task_alloc(struct task_struct *task) >> task->security = kzalloc(blob_sizes.lbs_task, GFP_KERNEL); >> if (task->security == NULL) >> return -ENOMEM; >> + >> + /* >> + * The start of the task blob contains the "display" LSM slot number. >> + * Start with it set to the invalid slot number, indicating that the >> + * default first registered LSM be displayed. >> + */ >> + display = task->security; >> + *display = LSMBLOB_INVALID; >> + >> return 0; >> } >> @@ -1563,14 +1579,24 @@ int security_file_open(struct file *file) >> int security_task_alloc(struct task_struct *task, unsigned long clone_flags) >> { >> + int *odisplay = current->security; >> + int *ndisplay; >> int rc = lsm_task_alloc(task); >> - if (rc) >> + if (unlikely(rc)) >> return rc; >> + >> rc = call_int_hook(task_alloc, 0, task, clone_flags); >> - if (unlikely(rc)) >> + if (unlikely(rc)) { >> security_task_free(task); >> - return rc; >> + return rc; >> + } >> + >> + ndisplay = task->security; >> + if (ndisplay && odisplay) >> + *ndisplay = *odisplay; >> + >> + return 0; >> } >> void security_task_free(struct task_struct *task) >> @@ -1967,10 +1993,29 @@ int security_getprocattr(struct task_struct *p, const char *lsm, char *name, >> char **value) >> { >> struct security_hook_list *hp; >> + int *display = current->security; >> + int slot = 0; >> + >> + if (!strcmp(name, "display")) { >> + /* >> + * lsm_slot will be 0 if there are no displaying modules. >> + */ >> + if (lsm_slot == 0) >> + return -EINVAL; >> + if (*display != LSMBLOB_INVALID) >> + slot = *display; >> + *value = kstrdup(lsm_slotlist[slot]->lsm, GFP_KERNEL); >> + if (*value) >> + return strlen(*value); >> + return -ENOMEM; >> + } >> hlist_for_each_entry(hp, &security_hook_heads.getprocattr, list) { >> if (lsm != NULL && strcmp(lsm, hp->lsmid->lsm)) >> continue; >> + if (lsm == NULL && *display != LSMBLOB_INVALID && >> + *display != hp->lsmid->slot) >> + continue; >> return hp->hook.getprocattr(p, name, value); >> } >> return -EINVAL; >> @@ -1980,10 +2025,46 @@ int security_setprocattr(const char *lsm, const char *name, void *value, >> size_t size) >> { >> struct security_hook_list *hp; >> + char *term; >> + char *cp; >> + int *display = current->security; >> + int rc = -EINVAL; >> + int slot = 0; >> + >> + if (!strcmp(name, "display")) { >> + /* >> + * lsm_slot will be 0 if there are no displaying modules. >> + */ >> + if (lsm_slot == 0 || size == 0) >> + return -EINVAL; >> + cp = kzalloc(size + 1, GFP_KERNEL); >> + if (cp == NULL) >> + return -ENOMEM; >> + memcpy(cp, value, size); >> + >> + term = strchr(cp, ' '); >> + if (term == NULL) >> + term = strchr(cp, '\n'); >> + if (term != NULL) >> + *term = '\0'; >> + >> + for (slot = 0; slot < lsm_slot; slot++) >> + if (!strcmp(cp, lsm_slotlist[slot]->lsm)) { >> + *display = lsm_slotlist[slot]->slot; >> + rc = size; >> + break; >> + } >> + >> + kfree(cp); >> + return rc; >> + } >> hlist_for_each_entry(hp, &security_hook_heads.setprocattr, list) { >> if (lsm != NULL && strcmp(lsm, hp->lsmid->lsm)) >> continue; >> + if (lsm == NULL && *display != LSMBLOB_INVALID && >> + *display != hp->lsmid->slot) >> + continue; >> return hp->hook.setprocattr(name, value, size); >> } >> return -EINVAL; >> @@ -2003,15 +2084,15 @@ EXPORT_SYMBOL(security_ismaclabel); >> int security_secid_to_secctx(struct lsmblob *blob, char **secdata, u32 *seclen) >> { >> struct security_hook_list *hp; >> - int rc; >> + int *display = current->security; >> hlist_for_each_entry(hp, &security_hook_heads.secid_to_secctx, list) { >> if (WARN_ON(hp->lsmid->slot < 0 || hp->lsmid->slot >= lsm_slot)) >> continue; >> - rc = hp->hook.secid_to_secctx(blob->secid[hp->lsmid->slot], >> - secdata, seclen); >> - if (rc != 0) >> - return rc; >> + if (*display == LSMBLOB_INVALID || *display == hp->lsmid->slot) >> + return hp->hook.secid_to_secctx( >> + blob->secid[hp->lsmid->slot], >> + secdata, seclen); >> } >> return 0; >> } >> @@ -2021,16 +2102,15 @@ int security_secctx_to_secid(const char *secdata, u32 seclen, >> struct lsmblob *blob) >> { >> struct security_hook_list *hp; >> - int rc; >> + int *display = current->security; >> lsmblob_init(blob, 0); >> hlist_for_each_entry(hp, &security_hook_heads.secctx_to_secid, list) { >> if (WARN_ON(hp->lsmid->slot < 0 || hp->lsmid->slot >= lsm_slot)) >> continue; >> - rc = hp->hook.secctx_to_secid(secdata, seclen, >> - &blob->secid[hp->lsmid->slot]); >> - if (rc != 0) >> - return rc; >> + if (*display == LSMBLOB_INVALID || *display == hp->lsmid->slot) >> + return hp->hook.secctx_to_secid(secdata, seclen, >> + &blob->secid[hp->lsmid->slot]); >> } >> return 0; >> } >> @@ -2038,7 +2118,15 @@ EXPORT_SYMBOL(security_secctx_to_secid); >> void security_release_secctx(char *secdata, u32 seclen) >> { >> - call_void_hook(release_secctx, secdata, seclen); >> + struct security_hook_list *hp; >> + int *display = current->security; >> + >> + hlist_for_each_entry(hp, &security_hook_heads.release_secctx, list) >> + if (*display == LSMBLOB_INVALID || >> + *display == hp->lsmid->slot) { >> + hp->hook.release_secctx(secdata, seclen); >> + return; >> + } >> } >> EXPORT_SYMBOL(security_release_secctx); >> @@ -2163,8 +2251,15 @@ EXPORT_SYMBOL(security_sock_rcv_skb); >> int security_socket_getpeersec_stream(struct socket *sock, char __user *optval, >> int __user *optlen, unsigned len) >> { >> - return call_int_hook(socket_getpeersec_stream, -ENOPROTOOPT, sock, >> - optval, optlen, len); >> + int *display = current->security; >> + struct security_hook_list *hp; >> + >> + hlist_for_each_entry(hp, &security_hook_heads.socket_getpeersec_stream, >> + list) >> + if (*display == LSMBLOB_INVALID || *display == hp->lsmid->slot) >> + return hp->hook.socket_getpeersec_stream(sock, optval, >> + optlen, len); >> + return -ENOPROTOOPT; >> } >> int security_socket_getpeersec_dgram(struct socket *sock, struct sk_buff *skb, >> >
On 6/28/19 9:15 AM, Casey Schaufler wrote: > On 6/28/2019 7:45 AM, Stephen Smalley wrote: >> On 6/26/19 3:22 PM, Casey Schaufler wrote: >>> Create a new entry "display" in /proc/.../attr for controlling >>> which LSM security information is displayed for a process. >>> The name of an active LSM that supplies hooks for human readable >>> data may be written to "display" to set the value. The name of >>> the LSM currently in use can be read from "display". >>> At this point there can only be one LSM capable of display >>> active. >> >> IIUC, presently, at the end of the entire series, >> >> 1) Any process can change its display attribute to any enabled security module, and no security module can veto that change. > > That is correct. If a security module could hoard the display it > could prevent user space from functioning in a multiple module > environment. > It should be noted that this is also just for legacy, we agreed last year that smack and apparmor would move to new none shared interfaces by default, and ideally other LSMs would as well. Smack has already added its process dir and apparmor has its in apparmor-next The display LSM allows for the current interfaces to be used in a stacking situation for things like LSM in legacy container. >> 2) The display attribute is inherited across fork and exec, even execs that change credentials, and again no security module has control over the inheritance of this attribute. > > Also correct. Scripts don't work otherwise. > >> >> 3) Setting the display attribute affects more than just the contexts read or written by the process itself: >> - Contexts reported in audit logs, >> - Contexts passed across binder (generated in sender context, delivered to receiver), >> - Contexts passed to NFS servers for new files, >> - Contexts returned by NFS servers for existing files, >> - Netlink-related contexts (?possibly generated in sender context rather than receiver context?), >> - This list may not be complete. > > Any of which can be changed should a more rational behavior be proposed. > One possibility is to use lsm='value',lsm='value' encoding for internal > communications, but there's been considerable resistance to anything > like that. > This is the part of the patchset that I am least happy with but it is a hard problem, and so far using display has been the only option that has been even sort of agreed to. >> 4) A security_secid_to_secctx() in one process' context (e.g. sender) or with one display value followed later by a security_secctx_to_secid() call in a different process' context (e.g. receiver) or with a different display value may ask a different security module to perform the reverse translation of the context than the forward translation. > > Do you have an example of where this might happen? > Contexts are rarely used within the kernel. The usual > behavior is to generate them, send them out to user space, > and delete them. They get cached in some networking code, > but not in cases where more than one (existing) security > module will ever use them. Binder may be an exception, but > only SELinux (currently) supports binder. > > >> Is that correct? If so, it seems problematic. > > Balancing backward compatibility with new behavior is hard! > What would you suggest for audit logs? Should we put all LSM > data in every record? If we could it would be better, but again how to do it. Every option presented has been rejected. > Is NFS a concern for anyone not using > SELinux? > Yes. Just because it isn't currently used doesn't mean it isn't a concern or desired. > There is no user space that uses display, and it's going > to take some time to work out all the kinks before we even > think about teaching systemd about it. > I'm not even sure we want to teach systemd et al. about it, it would be far better to teach them about /proc/*/attr/{smack,apparmor,...}/* But yes its going to take time to get the userspace updated.
On Fri, Jun 28, 2019 at 12:15 PM Casey Schaufler <casey@schaufler-ca.com> wrote: > > On 6/28/2019 7:45 AM, Stephen Smalley wrote: > > On 6/26/19 3:22 PM, Casey Schaufler wrote: > >> Create a new entry "display" in /proc/.../attr for controlling > >> which LSM security information is displayed for a process. > >> The name of an active LSM that supplies hooks for human readable > >> data may be written to "display" to set the value. The name of > >> the LSM currently in use can be read from "display". > >> At this point there can only be one LSM capable of display > >> active. > > > > IIUC, presently, at the end of the entire series, > > > > 1) Any process can change its display attribute to any enabled security module, and no security module can veto that change. > > That is correct. If a security module could hoard the display it > could prevent user space from functioning in a multiple module > environment. > > > 2) The display attribute is inherited across fork and exec, even execs that change credentials, and again no security module has control over the inheritance of this attribute. > > Also correct. Scripts don't work otherwise. It's a security hole waiting to happen. Unprivileged caller sets its display value to Smack on a mostly SELinux system that happens to enable Smack too, then exec's a credential-changing SELinux-aware program that uses one of the libselinux APIs to set one of the /proc/self/attr attributes to a different SELinux context. Due to the change in display, the SELinux-aware program instead ends up setting one of the Smack attributes and therefore the desired SELinux context is never applied to the process or file or socket or whatever. > > > > > 3) Setting the display attribute affects more than just the contexts read or written by the process itself: > > - Contexts reported in audit logs, > > - Contexts passed across binder (generated in sender context, delivered to receiver), > > - Contexts passed to NFS servers for new files, > > - Contexts returned by NFS servers for existing files, > > - Netlink-related contexts (?possibly generated in sender context rather than receiver context?), > > - This list may not be complete. > > Any of which can be changed should a more rational behavior be proposed. > One possibility is to use lsm='value',lsm='value' encoding for internal > communications, but there's been considerable resistance to anything > like that. These are also security holes waiting to happen. Processes can use it to hide their SELinux contexts from the audit logs, forge different SELinux contexts on binder IPC, forge file contexts to which they have no SELinux permissions on new files, ... All they need is stacking to be enabled and one other module that helpfully lets them set attribute values that look like SELinux contexts, and then they can set those and switch their display at the right time. > > > 4) A security_secid_to_secctx() in one process' context (e.g. sender) or with one display value followed later by a security_secctx_to_secid() call in a different process' context (e.g. receiver) or with a different display value may ask a different security module to perform the reverse translation of the context than the forward translation. > > Do you have an example of where this might happen? > Contexts are rarely used within the kernel. The usual > behavior is to generate them, send them out to user space, > and delete them. They get cached in some networking code, > but not in cases where more than one (existing) security > module will ever use them. Binder may be an exception, but > only SELinux (currently) supports binder. Haven't looked but I don't like the asymmetry of the interface. Doesn't matter that only SELinux supports binder if you ever want any other security module other than SELinux enabled at the same time as SELinux. > > > > Is that correct? If so, it seems problematic. > > Balancing backward compatibility with new behavior is hard! > What would you suggest for audit logs? Should we put all LSM > data in every record? Is NFS a concern for anyone not using > SELinux? Yes to all on audit if stacking is going to be real. And yes, I think other security modules will care about NFS if they are serious. > > There is no user space that uses display, and it's going > to take some time to work out all the kinks before we even > think about teaching systemd about it. That doesn't make it acceptable to introduce a mechanism that weakens security now. > > > > >> > >> Signed-off-by: Casey Schaufler <casey@schaufler-ca.com> > >> --- > >> fs/proc/base.c | 1 + > >> security/security.c | 129 ++++++++++++++++++++++++++++++++++++++------ > >> 2 files changed, 113 insertions(+), 17 deletions(-) > >> > >> diff --git a/fs/proc/base.c b/fs/proc/base.c > >> index ddef482f1334..7bf70e041315 100644 > >> --- a/fs/proc/base.c > >> +++ b/fs/proc/base.c > >> @@ -2618,6 +2618,7 @@ static const struct pid_entry attr_dir_stuff[] = { > >> ATTR(NULL, "fscreate", 0666), > >> ATTR(NULL, "keycreate", 0666), > >> ATTR(NULL, "sockcreate", 0666), > >> + ATTR(NULL, "display", 0666), > >> #ifdef CONFIG_SECURITY_SMACK > >> DIR("smack", 0555, > >> proc_smack_attr_dir_inode_ops, proc_smack_attr_dir_ops), > >> diff --git a/security/security.c b/security/security.c > >> index 3180a6f30625..82e29c477fa4 100644 > >> --- a/security/security.c > >> +++ b/security/security.c > >> @@ -46,7 +46,9 @@ static struct kmem_cache *lsm_file_cache; > >> static struct kmem_cache *lsm_inode_cache; > >> char *lsm_names; > >> -static struct lsm_blob_sizes blob_sizes __lsm_ro_after_init; > >> +static struct lsm_blob_sizes blob_sizes __lsm_ro_after_init = { > >> + .lbs_task = sizeof(int), /* slot number for the "display" LSM */ > >> +}; > >> /* Boot-time LSM user choice */ > >> static __initdata const char *chosen_lsm_order; > >> @@ -423,8 +425,10 @@ static int lsm_append(const char *new, char **result) > >> /* > >> * Current index to use while initializing the lsmblob secid list. > >> + * Pointers to the LSM id structures for local use. > >> */ > >> static int lsm_slot; > >> +static struct lsm_id *lsm_slotlist[LSMBLOB_ENTRIES]; > >> /** > >> * security_add_hooks - Add a modules hooks to the hook lists. > >> @@ -444,6 +448,7 @@ void __init security_add_hooks(struct security_hook_list *hooks, int count, > >> if (lsmid->slot == LSMBLOB_NEEDED) { > >> if (lsm_slot >= LSMBLOB_ENTRIES) > >> panic("%s Too many LSMs registered.\n", __func__); > >> + lsm_slotlist[lsm_slot] = lsmid; > >> lsmid->slot = lsm_slot++; > >> init_debug("%s assigned lsmblob slot %d\n", lsmid->lsm, > >> lsmid->slot); > >> @@ -564,6 +569,8 @@ int lsm_inode_alloc(struct inode *inode) > >> */ > >> static int lsm_task_alloc(struct task_struct *task) > >> { > >> + int *display; > >> + > >> if (blob_sizes.lbs_task == 0) { > >> task->security = NULL; > >> return 0; > >> @@ -572,6 +579,15 @@ static int lsm_task_alloc(struct task_struct *task) > >> task->security = kzalloc(blob_sizes.lbs_task, GFP_KERNEL); > >> if (task->security == NULL) > >> return -ENOMEM; > >> + > >> + /* > >> + * The start of the task blob contains the "display" LSM slot number. > >> + * Start with it set to the invalid slot number, indicating that the > >> + * default first registered LSM be displayed. > >> + */ > >> + display = task->security; > >> + *display = LSMBLOB_INVALID; > >> + > >> return 0; > >> } > >> @@ -1563,14 +1579,24 @@ int security_file_open(struct file *file) > >> int security_task_alloc(struct task_struct *task, unsigned long clone_flags) > >> { > >> + int *odisplay = current->security; > >> + int *ndisplay; > >> int rc = lsm_task_alloc(task); > >> - if (rc) > >> + if (unlikely(rc)) > >> return rc; > >> + > >> rc = call_int_hook(task_alloc, 0, task, clone_flags); > >> - if (unlikely(rc)) > >> + if (unlikely(rc)) { > >> security_task_free(task); > >> - return rc; > >> + return rc; > >> + } > >> + > >> + ndisplay = task->security; > >> + if (ndisplay && odisplay) > >> + *ndisplay = *odisplay; > >> + > >> + return 0; > >> } > >> void security_task_free(struct task_struct *task) > >> @@ -1967,10 +1993,29 @@ int security_getprocattr(struct task_struct *p, const char *lsm, char *name, > >> char **value) > >> { > >> struct security_hook_list *hp; > >> + int *display = current->security; > >> + int slot = 0; > >> + > >> + if (!strcmp(name, "display")) { > >> + /* > >> + * lsm_slot will be 0 if there are no displaying modules. > >> + */ > >> + if (lsm_slot == 0) > >> + return -EINVAL; > >> + if (*display != LSMBLOB_INVALID) > >> + slot = *display; > >> + *value = kstrdup(lsm_slotlist[slot]->lsm, GFP_KERNEL); > >> + if (*value) > >> + return strlen(*value); > >> + return -ENOMEM; > >> + } > >> hlist_for_each_entry(hp, &security_hook_heads.getprocattr, list) { > >> if (lsm != NULL && strcmp(lsm, hp->lsmid->lsm)) > >> continue; > >> + if (lsm == NULL && *display != LSMBLOB_INVALID && > >> + *display != hp->lsmid->slot) > >> + continue; > >> return hp->hook.getprocattr(p, name, value); > >> } > >> return -EINVAL; > >> @@ -1980,10 +2025,46 @@ int security_setprocattr(const char *lsm, const char *name, void *value, > >> size_t size) > >> { > >> struct security_hook_list *hp; > >> + char *term; > >> + char *cp; > >> + int *display = current->security; > >> + int rc = -EINVAL; > >> + int slot = 0; > >> + > >> + if (!strcmp(name, "display")) { > >> + /* > >> + * lsm_slot will be 0 if there are no displaying modules. > >> + */ > >> + if (lsm_slot == 0 || size == 0) > >> + return -EINVAL; > >> + cp = kzalloc(size + 1, GFP_KERNEL); > >> + if (cp == NULL) > >> + return -ENOMEM; > >> + memcpy(cp, value, size); > >> + > >> + term = strchr(cp, ' '); > >> + if (term == NULL) > >> + term = strchr(cp, '\n'); > >> + if (term != NULL) > >> + *term = '\0'; > >> + > >> + for (slot = 0; slot < lsm_slot; slot++) > >> + if (!strcmp(cp, lsm_slotlist[slot]->lsm)) { > >> + *display = lsm_slotlist[slot]->slot; > >> + rc = size; > >> + break; > >> + } > >> + > >> + kfree(cp); > >> + return rc; > >> + } > >> hlist_for_each_entry(hp, &security_hook_heads.setprocattr, list) { > >> if (lsm != NULL && strcmp(lsm, hp->lsmid->lsm)) > >> continue; > >> + if (lsm == NULL && *display != LSMBLOB_INVALID && > >> + *display != hp->lsmid->slot) > >> + continue; > >> return hp->hook.setprocattr(name, value, size); > >> } > >> return -EINVAL; > >> @@ -2003,15 +2084,15 @@ EXPORT_SYMBOL(security_ismaclabel); > >> int security_secid_to_secctx(struct lsmblob *blob, char **secdata, u32 *seclen) > >> { > >> struct security_hook_list *hp; > >> - int rc; > >> + int *display = current->security; > >> hlist_for_each_entry(hp, &security_hook_heads.secid_to_secctx, list) { > >> if (WARN_ON(hp->lsmid->slot < 0 || hp->lsmid->slot >= lsm_slot)) > >> continue; > >> - rc = hp->hook.secid_to_secctx(blob->secid[hp->lsmid->slot], > >> - secdata, seclen); > >> - if (rc != 0) > >> - return rc; > >> + if (*display == LSMBLOB_INVALID || *display == hp->lsmid->slot) > >> + return hp->hook.secid_to_secctx( > >> + blob->secid[hp->lsmid->slot], > >> + secdata, seclen); > >> } > >> return 0; > >> } > >> @@ -2021,16 +2102,15 @@ int security_secctx_to_secid(const char *secdata, u32 seclen, > >> struct lsmblob *blob) > >> { > >> struct security_hook_list *hp; > >> - int rc; > >> + int *display = current->security; > >> lsmblob_init(blob, 0); > >> hlist_for_each_entry(hp, &security_hook_heads.secctx_to_secid, list) { > >> if (WARN_ON(hp->lsmid->slot < 0 || hp->lsmid->slot >= lsm_slot)) > >> continue; > >> - rc = hp->hook.secctx_to_secid(secdata, seclen, > >> - &blob->secid[hp->lsmid->slot]); > >> - if (rc != 0) > >> - return rc; > >> + if (*display == LSMBLOB_INVALID || *display == hp->lsmid->slot) > >> + return hp->hook.secctx_to_secid(secdata, seclen, > >> + &blob->secid[hp->lsmid->slot]); > >> } > >> return 0; > >> } > >> @@ -2038,7 +2118,15 @@ EXPORT_SYMBOL(security_secctx_to_secid); > >> void security_release_secctx(char *secdata, u32 seclen) > >> { > >> - call_void_hook(release_secctx, secdata, seclen); > >> + struct security_hook_list *hp; > >> + int *display = current->security; > >> + > >> + hlist_for_each_entry(hp, &security_hook_heads.release_secctx, list) > >> + if (*display == LSMBLOB_INVALID || > >> + *display == hp->lsmid->slot) { > >> + hp->hook.release_secctx(secdata, seclen); > >> + return; > >> + } > >> } > >> EXPORT_SYMBOL(security_release_secctx); > >> @@ -2163,8 +2251,15 @@ EXPORT_SYMBOL(security_sock_rcv_skb); > >> int security_socket_getpeersec_stream(struct socket *sock, char __user *optval, > >> int __user *optlen, unsigned len) > >> { > >> - return call_int_hook(socket_getpeersec_stream, -ENOPROTOOPT, sock, > >> - optval, optlen, len); > >> + int *display = current->security; > >> + struct security_hook_list *hp; > >> + > >> + hlist_for_each_entry(hp, &security_hook_heads.socket_getpeersec_stream, > >> + list) > >> + if (*display == LSMBLOB_INVALID || *display == hp->lsmid->slot) > >> + return hp->hook.socket_getpeersec_stream(sock, optval, > >> + optlen, len); > >> + return -ENOPROTOOPT; > >> } > >> int security_socket_getpeersec_dgram(struct socket *sock, struct sk_buff *skb, > >> > >
On 6/28/2019 6:01 PM, Stephen Smalley wrote: > On Fri, Jun 28, 2019 at 12:15 PM Casey Schaufler <casey@schaufler-ca.com> wrote: >> On 6/28/2019 7:45 AM, Stephen Smalley wrote: >>> On 6/26/19 3:22 PM, Casey Schaufler wrote: >>>> Create a new entry "display" in /proc/.../attr for controlling >>>> which LSM security information is displayed for a process. >>>> The name of an active LSM that supplies hooks for human readable >>>> data may be written to "display" to set the value. The name of >>>> the LSM currently in use can be read from "display". >>>> At this point there can only be one LSM capable of display >>>> active. >>> IIUC, presently, at the end of the entire series, >>> >>> 1) Any process can change its display attribute to any enabled security module, and no security module can veto that change. >> That is correct. If a security module could hoard the display it >> could prevent user space from functioning in a multiple module >> environment. >> >>> 2) The display attribute is inherited across fork and exec, even execs that change credentials, and again no security module has control over the inheritance of this attribute. >> Also correct. Scripts don't work otherwise. > It's a security hole waiting to happen. Unprivileged caller sets its > display value to Smack on a mostly SELinux system that happens to > enable Smack too, then exec's a credential-changing SELinux-aware > program that uses one of the libselinux APIs to set one of the > /proc/self/attr attributes to a different SELinux context. Due to the > change in display, the SELinux-aware program instead ends up setting > one of the Smack attributes and therefore the desired SELinux context > is never applied to the process or file or socket or whatever. The credential-changing SELinux-aware program is getting invoked by an unprivileged, Smack aware program? Would anyone expect that to be a good idea? I'll admit it could happen, but setting the Smack label of your SELinux-aware program (which will need CAP_MAC_ADMIN, BTW) to "system_u:system_r:wheehee_t" is unlikely to result in anything other than your SELinux-aware program getting very frustrated. In the other direction, a Smack-aware program that trys to set its SELinux context to "^" is going to fail by SELinux policy. While I am willing to accept that it is possible that there is a way to exploit this, it would require convoluted SELinux and Smack policies. Anyone who has reason to use a combination of Smack and SELinux on a real system is already signing up for more configuration headaches than I would wish on anyone. I have strongly advocated addition of /proc/.../attr/ subdirectories for all LSMs, and that all user space migrate to using them. /proc/.../attr/selinux/current would not be affected by the display setting. We know, and have known for years that so long as "current" is shared there will be this sort of problem. > >>> 3) Setting the display attribute affects more than just the contexts read or written by the process itself: >>> - Contexts reported in audit logs, >>> - Contexts passed across binder (generated in sender context, delivered to receiver), >>> - Contexts passed to NFS servers for new files, >>> - Contexts returned by NFS servers for existing files, >>> - Netlink-related contexts (?possibly generated in sender context rather than receiver context?), >>> - This list may not be complete. >> Any of which can be changed should a more rational behavior be proposed. >> One possibility is to use lsm='value',lsm='value' encoding for internal >> communications, but there's been considerable resistance to anything >> like that. > These are also security holes waiting to happen. Processes can use it > to hide their SELinux contexts from the audit logs, forge different > SELinux contexts on binder IPC, forge file contexts to which they have > no SELinux permissions on new files, ... All they need is stacking to > be enabled and one other module that helpfully lets them set attribute > values that look like SELinux contexts, and then they can set those > and switch their display at the right time. What would you propose as a more rational behavior? Seriously, I could use some help here. >>> 4) A security_secid_to_secctx() in one process' context (e.g. sender) or with one display value followed later by a security_secctx_to_secid() call in a different process' context (e.g. receiver) or with a different display value may ask a different security module to perform the reverse translation of the context than the forward translation. >> Do you have an example of where this might happen? >> Contexts are rarely used within the kernel. The usual >> behavior is to generate them, send them out to user space, >> and delete them. They get cached in some networking code, >> but not in cases where more than one (existing) security >> module will ever use them. Binder may be an exception, but >> only SELinux (currently) supports binder. > Haven't looked but I don't like the asymmetry of the interface. > Doesn't matter that only SELinux supports binder if you ever want any > other security module other than SELinux enabled at the same time as > SELinux. Binder needs another look then. >> Is that correct? If so, it seems problematic. >> Balancing backward compatibility with new behavior is hard! >> What would you suggest for audit logs? Should we put all LSM >> data in every record? Is NFS a concern for anyone not using >> SELinux? > Yes to all on audit if stacking is going to be real. And yes, I think > other security modules will care about NFS if they are serious. I would love to get feedback from the audit maintainers about how they would like the multiple LSM data formatted. NFS is ... challenging. It was supposed to work with Smack when it went in, but to the best of my understanding never actually demonstrated. >> There is no user space that uses display, and it's going >> to take some time to work out all the kinks before we even >> think about teaching systemd about it. > That doesn't make it acceptable to introduce a mechanism that weakens > security now. Agreed in principle, not necessarily in detail.
On Fri, 28 Jun 2019, Stephen Smalley wrote: > > Balancing backward compatibility with new behavior is hard! > > What would you suggest for audit logs? Should we put all LSM > > data in every record? Is NFS a concern for anyone not using > > SELinux? > > Yes to all on audit if stacking is going to be real. And yes, I think > other security modules will care about NFS if they are serious. Agreed. There must better way to approach this, somehow...
On 7/1/2019 5:49 PM, James Morris wrote: > On Fri, 28 Jun 2019, Stephen Smalley wrote: > >>> Balancing backward compatibility with new behavior is hard! >>> What would you suggest for audit logs? Should we put all LSM >>> data in every record? Is NFS a concern for anyone not using >>> SELinux? >> Yes to all on audit if stacking is going to be real. And yes, I think >> other security modules will care about NFS if they are serious. > Agreed. > > There must better way to approach this, somehow... It not like I haven't proposed a number of mechanisms! The "display" mechanism has the best backward compatibility story, at the cost of being awkward/dangerous in the face of sophisticated user space environments. A combined string (smack='System",AppArmor='unconfined') sucks at compatibility, but provides the best information. Right now I'm looking at a way to prevent internal confusion. I think that may be possible. I'll point out that lib<lsm> has the option of verifying the display before doing scary writes, but that's a lot of work that no one is looking forward to.
diff --git a/fs/proc/base.c b/fs/proc/base.c index ddef482f1334..7bf70e041315 100644 --- a/fs/proc/base.c +++ b/fs/proc/base.c @@ -2618,6 +2618,7 @@ static const struct pid_entry attr_dir_stuff[] = { ATTR(NULL, "fscreate", 0666), ATTR(NULL, "keycreate", 0666), ATTR(NULL, "sockcreate", 0666), + ATTR(NULL, "display", 0666), #ifdef CONFIG_SECURITY_SMACK DIR("smack", 0555, proc_smack_attr_dir_inode_ops, proc_smack_attr_dir_ops), diff --git a/security/security.c b/security/security.c index 3180a6f30625..82e29c477fa4 100644 --- a/security/security.c +++ b/security/security.c @@ -46,7 +46,9 @@ static struct kmem_cache *lsm_file_cache; static struct kmem_cache *lsm_inode_cache; char *lsm_names; -static struct lsm_blob_sizes blob_sizes __lsm_ro_after_init; +static struct lsm_blob_sizes blob_sizes __lsm_ro_after_init = { + .lbs_task = sizeof(int), /* slot number for the "display" LSM */ +}; /* Boot-time LSM user choice */ static __initdata const char *chosen_lsm_order; @@ -423,8 +425,10 @@ static int lsm_append(const char *new, char **result) /* * Current index to use while initializing the lsmblob secid list. + * Pointers to the LSM id structures for local use. */ static int lsm_slot; +static struct lsm_id *lsm_slotlist[LSMBLOB_ENTRIES]; /** * security_add_hooks - Add a modules hooks to the hook lists. @@ -444,6 +448,7 @@ void __init security_add_hooks(struct security_hook_list *hooks, int count, if (lsmid->slot == LSMBLOB_NEEDED) { if (lsm_slot >= LSMBLOB_ENTRIES) panic("%s Too many LSMs registered.\n", __func__); + lsm_slotlist[lsm_slot] = lsmid; lsmid->slot = lsm_slot++; init_debug("%s assigned lsmblob slot %d\n", lsmid->lsm, lsmid->slot); @@ -564,6 +569,8 @@ int lsm_inode_alloc(struct inode *inode) */ static int lsm_task_alloc(struct task_struct *task) { + int *display; + if (blob_sizes.lbs_task == 0) { task->security = NULL; return 0; @@ -572,6 +579,15 @@ static int lsm_task_alloc(struct task_struct *task) task->security = kzalloc(blob_sizes.lbs_task, GFP_KERNEL); if (task->security == NULL) return -ENOMEM; + + /* + * The start of the task blob contains the "display" LSM slot number. + * Start with it set to the invalid slot number, indicating that the + * default first registered LSM be displayed. + */ + display = task->security; + *display = LSMBLOB_INVALID; + return 0; } @@ -1563,14 +1579,24 @@ int security_file_open(struct file *file) int security_task_alloc(struct task_struct *task, unsigned long clone_flags) { + int *odisplay = current->security; + int *ndisplay; int rc = lsm_task_alloc(task); - if (rc) + if (unlikely(rc)) return rc; + rc = call_int_hook(task_alloc, 0, task, clone_flags); - if (unlikely(rc)) + if (unlikely(rc)) { security_task_free(task); - return rc; + return rc; + } + + ndisplay = task->security; + if (ndisplay && odisplay) + *ndisplay = *odisplay; + + return 0; } void security_task_free(struct task_struct *task) @@ -1967,10 +1993,29 @@ int security_getprocattr(struct task_struct *p, const char *lsm, char *name, char **value) { struct security_hook_list *hp; + int *display = current->security; + int slot = 0; + + if (!strcmp(name, "display")) { + /* + * lsm_slot will be 0 if there are no displaying modules. + */ + if (lsm_slot == 0) + return -EINVAL; + if (*display != LSMBLOB_INVALID) + slot = *display; + *value = kstrdup(lsm_slotlist[slot]->lsm, GFP_KERNEL); + if (*value) + return strlen(*value); + return -ENOMEM; + } hlist_for_each_entry(hp, &security_hook_heads.getprocattr, list) { if (lsm != NULL && strcmp(lsm, hp->lsmid->lsm)) continue; + if (lsm == NULL && *display != LSMBLOB_INVALID && + *display != hp->lsmid->slot) + continue; return hp->hook.getprocattr(p, name, value); } return -EINVAL; @@ -1980,10 +2025,46 @@ int security_setprocattr(const char *lsm, const char *name, void *value, size_t size) { struct security_hook_list *hp; + char *term; + char *cp; + int *display = current->security; + int rc = -EINVAL; + int slot = 0; + + if (!strcmp(name, "display")) { + /* + * lsm_slot will be 0 if there are no displaying modules. + */ + if (lsm_slot == 0 || size == 0) + return -EINVAL; + cp = kzalloc(size + 1, GFP_KERNEL); + if (cp == NULL) + return -ENOMEM; + memcpy(cp, value, size); + + term = strchr(cp, ' '); + if (term == NULL) + term = strchr(cp, '\n'); + if (term != NULL) + *term = '\0'; + + for (slot = 0; slot < lsm_slot; slot++) + if (!strcmp(cp, lsm_slotlist[slot]->lsm)) { + *display = lsm_slotlist[slot]->slot; + rc = size; + break; + } + + kfree(cp); + return rc; + } hlist_for_each_entry(hp, &security_hook_heads.setprocattr, list) { if (lsm != NULL && strcmp(lsm, hp->lsmid->lsm)) continue; + if (lsm == NULL && *display != LSMBLOB_INVALID && + *display != hp->lsmid->slot) + continue; return hp->hook.setprocattr(name, value, size); } return -EINVAL; @@ -2003,15 +2084,15 @@ EXPORT_SYMBOL(security_ismaclabel); int security_secid_to_secctx(struct lsmblob *blob, char **secdata, u32 *seclen) { struct security_hook_list *hp; - int rc; + int *display = current->security; hlist_for_each_entry(hp, &security_hook_heads.secid_to_secctx, list) { if (WARN_ON(hp->lsmid->slot < 0 || hp->lsmid->slot >= lsm_slot)) continue; - rc = hp->hook.secid_to_secctx(blob->secid[hp->lsmid->slot], - secdata, seclen); - if (rc != 0) - return rc; + if (*display == LSMBLOB_INVALID || *display == hp->lsmid->slot) + return hp->hook.secid_to_secctx( + blob->secid[hp->lsmid->slot], + secdata, seclen); } return 0; } @@ -2021,16 +2102,15 @@ int security_secctx_to_secid(const char *secdata, u32 seclen, struct lsmblob *blob) { struct security_hook_list *hp; - int rc; + int *display = current->security; lsmblob_init(blob, 0); hlist_for_each_entry(hp, &security_hook_heads.secctx_to_secid, list) { if (WARN_ON(hp->lsmid->slot < 0 || hp->lsmid->slot >= lsm_slot)) continue; - rc = hp->hook.secctx_to_secid(secdata, seclen, - &blob->secid[hp->lsmid->slot]); - if (rc != 0) - return rc; + if (*display == LSMBLOB_INVALID || *display == hp->lsmid->slot) + return hp->hook.secctx_to_secid(secdata, seclen, + &blob->secid[hp->lsmid->slot]); } return 0; } @@ -2038,7 +2118,15 @@ EXPORT_SYMBOL(security_secctx_to_secid); void security_release_secctx(char *secdata, u32 seclen) { - call_void_hook(release_secctx, secdata, seclen); + struct security_hook_list *hp; + int *display = current->security; + + hlist_for_each_entry(hp, &security_hook_heads.release_secctx, list) + if (*display == LSMBLOB_INVALID || + *display == hp->lsmid->slot) { + hp->hook.release_secctx(secdata, seclen); + return; + } } EXPORT_SYMBOL(security_release_secctx); @@ -2163,8 +2251,15 @@ EXPORT_SYMBOL(security_sock_rcv_skb); int security_socket_getpeersec_stream(struct socket *sock, char __user *optval, int __user *optlen, unsigned len) { - return call_int_hook(socket_getpeersec_stream, -ENOPROTOOPT, sock, - optval, optlen, len); + int *display = current->security; + struct security_hook_list *hp; + + hlist_for_each_entry(hp, &security_hook_heads.socket_getpeersec_stream, + list) + if (*display == LSMBLOB_INVALID || *display == hp->lsmid->slot) + return hp->hook.socket_getpeersec_stream(sock, optval, + optlen, len); + return -ENOPROTOOPT; } int security_socket_getpeersec_dgram(struct socket *sock, struct sk_buff *skb,
Create a new entry "display" in /proc/.../attr for controlling which LSM security information is displayed for a process. The name of an active LSM that supplies hooks for human readable data may be written to "display" to set the value. The name of the LSM currently in use can be read from "display". At this point there can only be one LSM capable of display active. Signed-off-by: Casey Schaufler <casey@schaufler-ca.com> --- fs/proc/base.c | 1 + security/security.c | 129 ++++++++++++++++++++++++++++++++++++++------ 2 files changed, 113 insertions(+), 17 deletions(-)