| Message ID | 20190410165519.209565-1-mortonm@chromium.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [01/10] LSM: SafeSetID: fix pr_warn() to include newline | expand |
On Wed, Apr 10, 2019 at 9:55 AM Micah Morton <mortonm@chromium.org> wrote: > > From: Jann Horn <jannh@google.com> > > With the old code, when a process with the (real,effective,saved) UID set > (1,1,1) calls setresuid(2,3,4), safesetid_task_fix_setuid() only checks > whether the transition 1->2 is permitted; the transitions 1->3 and 1->4 are > not checked. Fix this. > > This is also a good opportunity to refactor safesetid_task_fix_setuid() to > be less verbose - having one branch per set*uid() syscall is unnecessary. > > Note that this slightly changes semantics: The UID transition check for > UIDs that were not in the old cred struct is now always performed against > the policy of the RUID. I think that's more consistent anyway, since the > RUID is also the one that decides whether any policy is enforced at all. > > Signed-off-by: Jann Horn <jannh@google.com> > Signed-off-by: Micah Morton <mortonm@chromium.org> Reviewed-by: Kees Cook <keescook@chromium.org> -Kees > --- > security/safesetid/lsm.c | 125 +++++++++++---------------------------- > 1 file changed, 35 insertions(+), 90 deletions(-) > > diff --git a/security/safesetid/lsm.c b/security/safesetid/lsm.c > index 2daecab3a4c0..5310fcf3052a 100644 > --- a/security/safesetid/lsm.c > +++ b/security/safesetid/lsm.c > @@ -99,20 +99,30 @@ static int safesetid_security_capable(const struct cred *cred, > return 0; > } > > -static int check_uid_transition(kuid_t parent, kuid_t child) > +/* > + * Check whether a caller with old credentials @old is allowed to switch to > + * credentials that contain @new_uid. > + */ > +static bool uid_permitted_for_cred(const struct cred *old, kuid_t new_uid) > { > - if (check_setuid_policy_hashtable_key_value(parent, child)) > - return 0; > - pr_warn("UID transition (%d -> %d) blocked\n", > - __kuid_val(parent), > - __kuid_val(child)); > + bool permitted; > + > + /* If our old creds already had this UID in it, it's fine. */ > + if (uid_eq(new_uid, old->uid) || uid_eq(new_uid, old->euid) || > + uid_eq(new_uid, old->suid)) > + return true; > + > /* > - * Kill this process to avoid potential security vulnerabilities > - * that could arise from a missing whitelist entry preventing a > - * privileged process from dropping to a lesser-privileged one. > + * Transitions to new UIDs require a check against the policy of the old > + * RUID. > */ > - force_sig(SIGKILL, current); > - return -EACCES; > + permitted = check_setuid_policy_hashtable_key_value(old->uid, new_uid); > + if (!permitted) { > + pr_warn("UID transition ((%d,%d,%d) -> %d) blocked\n", > + __kuid_val(old->uid), __kuid_val(old->euid), > + __kuid_val(old->suid), __kuid_val(new_uid)); > + } > + return permitted; > } > > /* > @@ -125,88 +135,23 @@ static int safesetid_task_fix_setuid(struct cred *new, > int flags) > { > > - /* Do nothing if there are no setuid restrictions for this UID. */ > + /* Do nothing if there are no setuid restrictions for our old RUID. */ > if (!check_setuid_policy_hashtable_key(old->uid)) > return 0; > > - switch (flags) { > - case LSM_SETID_RE: > - /* > - * Users for which setuid restrictions exist can only set the > - * real UID to the real UID or the effective UID, unless an > - * explicit whitelist policy allows the transition. > - */ > - if (!uid_eq(old->uid, new->uid) && > - !uid_eq(old->euid, new->uid)) { > - return check_uid_transition(old->uid, new->uid); > - } > - /* > - * Users for which setuid restrictions exist can only set the > - * effective UID to the real UID, the effective UID, or the > - * saved set-UID, unless an explicit whitelist policy allows > - * the transition. > - */ > - if (!uid_eq(old->uid, new->euid) && > - !uid_eq(old->euid, new->euid) && > - !uid_eq(old->suid, new->euid)) { > - return check_uid_transition(old->euid, new->euid); > - } > - break; > - case LSM_SETID_ID: > - /* > - * Users for which setuid restrictions exist cannot change the > - * real UID or saved set-UID unless an explicit whitelist > - * policy allows the transition. > - */ > - if (!uid_eq(old->uid, new->uid)) > - return check_uid_transition(old->uid, new->uid); > - if (!uid_eq(old->suid, new->suid)) > - return check_uid_transition(old->suid, new->suid); > - break; > - case LSM_SETID_RES: > - /* > - * Users for which setuid restrictions exist cannot change the > - * real UID, effective UID, or saved set-UID to anything but > - * one of: the current real UID, the current effective UID or > - * the current saved set-user-ID unless an explicit whitelist > - * policy allows the transition. > - */ > - if (!uid_eq(new->uid, old->uid) && > - !uid_eq(new->uid, old->euid) && > - !uid_eq(new->uid, old->suid)) { > - return check_uid_transition(old->uid, new->uid); > - } > - if (!uid_eq(new->euid, old->uid) && > - !uid_eq(new->euid, old->euid) && > - !uid_eq(new->euid, old->suid)) { > - return check_uid_transition(old->euid, new->euid); > - } > - if (!uid_eq(new->suid, old->uid) && > - !uid_eq(new->suid, old->euid) && > - !uid_eq(new->suid, old->suid)) { > - return check_uid_transition(old->suid, new->suid); > - } > - break; > - case LSM_SETID_FS: > - /* > - * Users for which setuid restrictions exist cannot change the > - * filesystem UID to anything but one of: the current real UID, > - * the current effective UID or the current saved set-UID > - * unless an explicit whitelist policy allows the transition. > - */ > - if (!uid_eq(new->fsuid, old->uid) && > - !uid_eq(new->fsuid, old->euid) && > - !uid_eq(new->fsuid, old->suid) && > - !uid_eq(new->fsuid, old->fsuid)) { > - return check_uid_transition(old->fsuid, new->fsuid); > - } > - break; > - default: > - pr_warn("Unknown setid state %d\n", flags); > - force_sig(SIGKILL, current); > - return -EINVAL; > - } > - return 0; > + if (uid_permitted_for_cred(old, new->uid) && > + uid_permitted_for_cred(old, new->euid) && > + uid_permitted_for_cred(old, new->suid) && > + uid_permitted_for_cred(old, new->fsuid)) > + return 0; > + > + /* > + * Kill this process to avoid potential security vulnerabilities > + * that could arise from a missing whitelist entry preventing a > + * privileged process from dropping to a lesser-privileged one. > + */ > + force_sig(SIGKILL, current); > + return -EACCES; > } > > int add_safesetid_whitelist_entry(kuid_t parent, kuid_t child) > -- > 2.21.0.392.gf8f6787159e-goog >
Ready for merge. On Wed, Apr 10, 2019 at 10:11 AM Kees Cook <keescook@chromium.org> wrote: > > On Wed, Apr 10, 2019 at 9:55 AM Micah Morton <mortonm@chromium.org> wrote: > > > > From: Jann Horn <jannh@google.com> > > > > With the old code, when a process with the (real,effective,saved) UID set > > (1,1,1) calls setresuid(2,3,4), safesetid_task_fix_setuid() only checks > > whether the transition 1->2 is permitted; the transitions 1->3 and 1->4 are > > not checked. Fix this. > > > > This is also a good opportunity to refactor safesetid_task_fix_setuid() to > > be less verbose - having one branch per set*uid() syscall is unnecessary. > > > > Note that this slightly changes semantics: The UID transition check for > > UIDs that were not in the old cred struct is now always performed against > > the policy of the RUID. I think that's more consistent anyway, since the > > RUID is also the one that decides whether any policy is enforced at all. > > > > Signed-off-by: Jann Horn <jannh@google.com> > > Signed-off-by: Micah Morton <mortonm@chromium.org> > > Reviewed-by: Kees Cook <keescook@chromium.org> > > -Kees > > > --- > > security/safesetid/lsm.c | 125 +++++++++++---------------------------- > > 1 file changed, 35 insertions(+), 90 deletions(-) > > > > diff --git a/security/safesetid/lsm.c b/security/safesetid/lsm.c > > index 2daecab3a4c0..5310fcf3052a 100644 > > --- a/security/safesetid/lsm.c > > +++ b/security/safesetid/lsm.c > > @@ -99,20 +99,30 @@ static int safesetid_security_capable(const struct cred *cred, > > return 0; > > } > > > > -static int check_uid_transition(kuid_t parent, kuid_t child) > > +/* > > + * Check whether a caller with old credentials @old is allowed to switch to > > + * credentials that contain @new_uid. > > + */ > > +static bool uid_permitted_for_cred(const struct cred *old, kuid_t new_uid) > > { > > - if (check_setuid_policy_hashtable_key_value(parent, child)) > > - return 0; > > - pr_warn("UID transition (%d -> %d) blocked\n", > > - __kuid_val(parent), > > - __kuid_val(child)); > > + bool permitted; > > + > > + /* If our old creds already had this UID in it, it's fine. */ > > + if (uid_eq(new_uid, old->uid) || uid_eq(new_uid, old->euid) || > > + uid_eq(new_uid, old->suid)) > > + return true; > > + > > /* > > - * Kill this process to avoid potential security vulnerabilities > > - * that could arise from a missing whitelist entry preventing a > > - * privileged process from dropping to a lesser-privileged one. > > + * Transitions to new UIDs require a check against the policy of the old > > + * RUID. > > */ > > - force_sig(SIGKILL, current); > > - return -EACCES; > > + permitted = check_setuid_policy_hashtable_key_value(old->uid, new_uid); > > + if (!permitted) { > > + pr_warn("UID transition ((%d,%d,%d) -> %d) blocked\n", > > + __kuid_val(old->uid), __kuid_val(old->euid), > > + __kuid_val(old->suid), __kuid_val(new_uid)); > > + } > > + return permitted; > > } > > > > /* > > @@ -125,88 +135,23 @@ static int safesetid_task_fix_setuid(struct cred *new, > > int flags) > > { > > > > - /* Do nothing if there are no setuid restrictions for this UID. */ > > + /* Do nothing if there are no setuid restrictions for our old RUID. */ > > if (!check_setuid_policy_hashtable_key(old->uid)) > > return 0; > > > > - switch (flags) { > > - case LSM_SETID_RE: > > - /* > > - * Users for which setuid restrictions exist can only set the > > - * real UID to the real UID or the effective UID, unless an > > - * explicit whitelist policy allows the transition. > > - */ > > - if (!uid_eq(old->uid, new->uid) && > > - !uid_eq(old->euid, new->uid)) { > > - return check_uid_transition(old->uid, new->uid); > > - } > > - /* > > - * Users for which setuid restrictions exist can only set the > > - * effective UID to the real UID, the effective UID, or the > > - * saved set-UID, unless an explicit whitelist policy allows > > - * the transition. > > - */ > > - if (!uid_eq(old->uid, new->euid) && > > - !uid_eq(old->euid, new->euid) && > > - !uid_eq(old->suid, new->euid)) { > > - return check_uid_transition(old->euid, new->euid); > > - } > > - break; > > - case LSM_SETID_ID: > > - /* > > - * Users for which setuid restrictions exist cannot change the > > - * real UID or saved set-UID unless an explicit whitelist > > - * policy allows the transition. > > - */ > > - if (!uid_eq(old->uid, new->uid)) > > - return check_uid_transition(old->uid, new->uid); > > - if (!uid_eq(old->suid, new->suid)) > > - return check_uid_transition(old->suid, new->suid); > > - break; > > - case LSM_SETID_RES: > > - /* > > - * Users for which setuid restrictions exist cannot change the > > - * real UID, effective UID, or saved set-UID to anything but > > - * one of: the current real UID, the current effective UID or > > - * the current saved set-user-ID unless an explicit whitelist > > - * policy allows the transition. > > - */ > > - if (!uid_eq(new->uid, old->uid) && > > - !uid_eq(new->uid, old->euid) && > > - !uid_eq(new->uid, old->suid)) { > > - return check_uid_transition(old->uid, new->uid); > > - } > > - if (!uid_eq(new->euid, old->uid) && > > - !uid_eq(new->euid, old->euid) && > > - !uid_eq(new->euid, old->suid)) { > > - return check_uid_transition(old->euid, new->euid); > > - } > > - if (!uid_eq(new->suid, old->uid) && > > - !uid_eq(new->suid, old->euid) && > > - !uid_eq(new->suid, old->suid)) { > > - return check_uid_transition(old->suid, new->suid); > > - } > > - break; > > - case LSM_SETID_FS: > > - /* > > - * Users for which setuid restrictions exist cannot change the > > - * filesystem UID to anything but one of: the current real UID, > > - * the current effective UID or the current saved set-UID > > - * unless an explicit whitelist policy allows the transition. > > - */ > > - if (!uid_eq(new->fsuid, old->uid) && > > - !uid_eq(new->fsuid, old->euid) && > > - !uid_eq(new->fsuid, old->suid) && > > - !uid_eq(new->fsuid, old->fsuid)) { > > - return check_uid_transition(old->fsuid, new->fsuid); > > - } > > - break; > > - default: > > - pr_warn("Unknown setid state %d\n", flags); > > - force_sig(SIGKILL, current); > > - return -EINVAL; > > - } > > - return 0; > > + if (uid_permitted_for_cred(old, new->uid) && > > + uid_permitted_for_cred(old, new->euid) && > > + uid_permitted_for_cred(old, new->suid) && > > + uid_permitted_for_cred(old, new->fsuid)) > > + return 0; > > + > > + /* > > + * Kill this process to avoid potential security vulnerabilities > > + * that could arise from a missing whitelist entry preventing a > > + * privileged process from dropping to a lesser-privileged one. > > + */ > > + force_sig(SIGKILL, current); > > + return -EACCES; > > } > > > > int add_safesetid_whitelist_entry(kuid_t parent, kuid_t child) > > -- > > 2.21.0.392.gf8f6787159e-goog > > > > > -- > Kees Cook
diff --git a/security/safesetid/lsm.c b/security/safesetid/lsm.c index 2daecab3a4c0..5310fcf3052a 100644 --- a/security/safesetid/lsm.c +++ b/security/safesetid/lsm.c @@ -99,20 +99,30 @@ static int safesetid_security_capable(const struct cred *cred, return 0; } -static int check_uid_transition(kuid_t parent, kuid_t child) +/* + * Check whether a caller with old credentials @old is allowed to switch to + * credentials that contain @new_uid. + */ +static bool uid_permitted_for_cred(const struct cred *old, kuid_t new_uid) { - if (check_setuid_policy_hashtable_key_value(parent, child)) - return 0; - pr_warn("UID transition (%d -> %d) blocked\n", - __kuid_val(parent), - __kuid_val(child)); + bool permitted; + + /* If our old creds already had this UID in it, it's fine. */ + if (uid_eq(new_uid, old->uid) || uid_eq(new_uid, old->euid) || + uid_eq(new_uid, old->suid)) + return true; + /* - * Kill this process to avoid potential security vulnerabilities - * that could arise from a missing whitelist entry preventing a - * privileged process from dropping to a lesser-privileged one. + * Transitions to new UIDs require a check against the policy of the old + * RUID. */ - force_sig(SIGKILL, current); - return -EACCES; + permitted = check_setuid_policy_hashtable_key_value(old->uid, new_uid); + if (!permitted) { + pr_warn("UID transition ((%d,%d,%d) -> %d) blocked\n", + __kuid_val(old->uid), __kuid_val(old->euid), + __kuid_val(old->suid), __kuid_val(new_uid)); + } + return permitted; } /* @@ -125,88 +135,23 @@ static int safesetid_task_fix_setuid(struct cred *new, int flags) { - /* Do nothing if there are no setuid restrictions for this UID. */ + /* Do nothing if there are no setuid restrictions for our old RUID. */ if (!check_setuid_policy_hashtable_key(old->uid)) return 0; - switch (flags) { - case LSM_SETID_RE: - /* - * Users for which setuid restrictions exist can only set the - * real UID to the real UID or the effective UID, unless an - * explicit whitelist policy allows the transition. - */ - if (!uid_eq(old->uid, new->uid) && - !uid_eq(old->euid, new->uid)) { - return check_uid_transition(old->uid, new->uid); - } - /* - * Users for which setuid restrictions exist can only set the - * effective UID to the real UID, the effective UID, or the - * saved set-UID, unless an explicit whitelist policy allows - * the transition. - */ - if (!uid_eq(old->uid, new->euid) && - !uid_eq(old->euid, new->euid) && - !uid_eq(old->suid, new->euid)) { - return check_uid_transition(old->euid, new->euid); - } - break; - case LSM_SETID_ID: - /* - * Users for which setuid restrictions exist cannot change the - * real UID or saved set-UID unless an explicit whitelist - * policy allows the transition. - */ - if (!uid_eq(old->uid, new->uid)) - return check_uid_transition(old->uid, new->uid); - if (!uid_eq(old->suid, new->suid)) - return check_uid_transition(old->suid, new->suid); - break; - case LSM_SETID_RES: - /* - * Users for which setuid restrictions exist cannot change the - * real UID, effective UID, or saved set-UID to anything but - * one of: the current real UID, the current effective UID or - * the current saved set-user-ID unless an explicit whitelist - * policy allows the transition. - */ - if (!uid_eq(new->uid, old->uid) && - !uid_eq(new->uid, old->euid) && - !uid_eq(new->uid, old->suid)) { - return check_uid_transition(old->uid, new->uid); - } - if (!uid_eq(new->euid, old->uid) && - !uid_eq(new->euid, old->euid) && - !uid_eq(new->euid, old->suid)) { - return check_uid_transition(old->euid, new->euid); - } - if (!uid_eq(new->suid, old->uid) && - !uid_eq(new->suid, old->euid) && - !uid_eq(new->suid, old->suid)) { - return check_uid_transition(old->suid, new->suid); - } - break; - case LSM_SETID_FS: - /* - * Users for which setuid restrictions exist cannot change the - * filesystem UID to anything but one of: the current real UID, - * the current effective UID or the current saved set-UID - * unless an explicit whitelist policy allows the transition. - */ - if (!uid_eq(new->fsuid, old->uid) && - !uid_eq(new->fsuid, old->euid) && - !uid_eq(new->fsuid, old->suid) && - !uid_eq(new->fsuid, old->fsuid)) { - return check_uid_transition(old->fsuid, new->fsuid); - } - break; - default: - pr_warn("Unknown setid state %d\n", flags); - force_sig(SIGKILL, current); - return -EINVAL; - } - return 0; + if (uid_permitted_for_cred(old, new->uid) && + uid_permitted_for_cred(old, new->euid) && + uid_permitted_for_cred(old, new->suid) && + uid_permitted_for_cred(old, new->fsuid)) + return 0; + + /* + * Kill this process to avoid potential security vulnerabilities + * that could arise from a missing whitelist entry preventing a + * privileged process from dropping to a lesser-privileged one. + */ + force_sig(SIGKILL, current); + return -EACCES; } int add_safesetid_whitelist_entry(kuid_t parent, kuid_t child)