| Message ID | 20181010161430.11633-2-laurent@vivier.eu (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | ns: introduce binfmt_misc namespace | expand |
On 2018-10-10 18:14, Laurent Vivier wrote: > + /* create a new binfmt namespace > + * if we are not in the first user namespace > + * but the binfmt namespace is the first one > + */ > + if (READ_ONCE(ns->binfmt_ns) == NULL) { > + struct binfmt_namespace *new_ns; > + > + new_ns = kmalloc(sizeof(struct binfmt_namespace), > + GFP_KERNEL); > + if (new_ns == NULL) > + return -ENOMEM; > + INIT_LIST_HEAD(&new_ns->entries); > + new_ns->enabled = 1; > + rwlock_init(&new_ns->entries_lock); > + new_ns->bm_mnt = NULL; > + new_ns->entry_count = 0; > + /* ensure new_ns is completely initialized before sharing it */ > + smp_wmb(); > + WRITE_ONCE(ns->binfmt_ns, new_ns); > + } If ns->binfmt_ns can really change under us (given you use READ_ONCE), what prevents two instances of this code running at the same time, in which case one of them would leak its new_ns instance? Also, there doesn't seem to be any smp_rmb() buddy to that wmb(), I don't think that's implied by READ_ONCE() in binfmt_ns(). Rasmus
Le 16/10/2018 à 12:13, Rasmus Villemoes a écrit : > On 2018-10-10 18:14, Laurent Vivier wrote: > >> + /* create a new binfmt namespace >> + * if we are not in the first user namespace >> + * but the binfmt namespace is the first one >> + */ >> + if (READ_ONCE(ns->binfmt_ns) == NULL) { >> + struct binfmt_namespace *new_ns; >> + >> + new_ns = kmalloc(sizeof(struct binfmt_namespace), >> + GFP_KERNEL); >> + if (new_ns == NULL) >> + return -ENOMEM; >> + INIT_LIST_HEAD(&new_ns->entries); >> + new_ns->enabled = 1; >> + rwlock_init(&new_ns->entries_lock); >> + new_ns->bm_mnt = NULL; >> + new_ns->entry_count = 0; >> + /* ensure new_ns is completely initialized before sharing it */ >> + smp_wmb(); >> + WRITE_ONCE(ns->binfmt_ns, new_ns); >> + } > > If ns->binfmt_ns can really change under us (given you use READ_ONCE), > what prevents two instances of this code running at the same time, in > which case one of them would leak its new_ns instance? Also, there See https://www.mail-archive.com/linux-kernel@vger.kernel.org/msg1782780.html > doesn't seem to be any smp_rmb() buddy to that wmb(), I don't think > that's implied by READ_ONCE() in binfmt_ns(). See https://www.mail-archive.com/linux-kernel@vger.kernel.org/msg1783049.html Thanks, Laurent
On Wed, Oct 10, 2018 at 06:14:30PM +0200, Laurent Vivier wrote: > This patch allows to have a different binfmt_misc configuration > for each new user namespace. By default, the binfmt_misc configuration > is the one of the previous level, but if the binfmt_misc filesystem is > mounted in the new namespace a new empty binfmt instance is created and > used in this namespace. > > For instance, using "unshare" we can start a chroot of another > architecture and configure the binfmt_misc interpreter without being root > to run the binaries in this chroot. > > Signed-off-by: Laurent Vivier <laurent@vivier.eu> Acked-by: Andrei Vagin <avagin@gmail.com> Thanks, Andrei > --- > fs/binfmt_misc.c | 111 ++++++++++++++++++++++++--------- > include/linux/user_namespace.h | 15 +++++ > kernel/user.c | 14 +++++ > kernel/user_namespace.c | 3 + > 4 files changed, 115 insertions(+), 28 deletions(-) > > diff --git a/fs/binfmt_misc.c b/fs/binfmt_misc.c > index aa4a7a23ff99..df9dc3248b7b 100644 > --- a/fs/binfmt_misc.c > +++ b/fs/binfmt_misc.c > @@ -38,9 +38,6 @@ enum { > VERBOSE_STATUS = 1 /* make it zero to save 400 bytes kernel memory */ > }; > > -static LIST_HEAD(entries); > -static int enabled = 1; > - > enum {Enabled, Magic}; > #define MISC_FMT_PRESERVE_ARGV0 (1 << 31) > #define MISC_FMT_OPEN_BINARY (1 << 30) > @@ -60,10 +57,7 @@ typedef struct { > struct file *interp_file; > } Node; > > -static DEFINE_RWLOCK(entries_lock); > static struct file_system_type bm_fs_type; > -static struct vfsmount *bm_mnt; > -static int entry_count; > > /* > * Max length of the register string. Determined by: > @@ -80,18 +74,37 @@ static int entry_count; > */ > #define MAX_REGISTER_LENGTH 1920 > > +static struct binfmt_namespace *binfmt_ns(struct user_namespace *ns) > +{ > + struct binfmt_namespace *b_ns; > + > + while (ns) { > + b_ns = READ_ONCE(ns->binfmt_ns); > + if (b_ns) > + return b_ns; > + ns = ns->parent; > + } > + /* as the first user namespace is initialized with > + * &init_binfmt_ns we should never come here > + * but we try to stay safe by logging a warning > + * and returning a sane value > + */ > + WARN_ON_ONCE(1); > + return &init_binfmt_ns; > +} > + > /* > * Check if we support the binfmt > * if we do, return the node, else NULL > * locking is done in load_misc_binary > */ > -static Node *check_file(struct linux_binprm *bprm) > +static Node *check_file(struct binfmt_namespace *ns, struct linux_binprm *bprm) > { > char *p = strrchr(bprm->interp, '.'); > struct list_head *l; > > /* Walk all the registered handlers. */ > - list_for_each(l, &entries) { > + list_for_each(l, &ns->entries) { > Node *e = list_entry(l, Node, list); > char *s; > int j; > @@ -133,17 +146,18 @@ static int load_misc_binary(struct linux_binprm *bprm) > struct file *interp_file = NULL; > int retval; > int fd_binary = -1; > + struct binfmt_namespace *ns = binfmt_ns(current_user_ns()); > > retval = -ENOEXEC; > - if (!enabled) > + if (!ns->enabled) > return retval; > > /* to keep locking time low, we copy the interpreter string */ > - read_lock(&entries_lock); > - fmt = check_file(bprm); > + read_lock(&ns->entries_lock); > + fmt = check_file(ns, bprm); > if (fmt) > dget(fmt->dentry); > - read_unlock(&entries_lock); > + read_unlock(&ns->entries_lock); > if (!fmt) > return retval; > > @@ -609,19 +623,19 @@ static void bm_evict_inode(struct inode *inode) > kfree(e); > } > > -static void kill_node(Node *e) > +static void kill_node(struct binfmt_namespace *ns, Node *e) > { > struct dentry *dentry; > > - write_lock(&entries_lock); > + write_lock(&ns->entries_lock); > list_del_init(&e->list); > - write_unlock(&entries_lock); > + write_unlock(&ns->entries_lock); > > dentry = e->dentry; > drop_nlink(d_inode(dentry)); > d_drop(dentry); > dput(dentry); > - simple_release_fs(&bm_mnt, &entry_count); > + simple_release_fs(&ns->bm_mnt, &ns->entry_count); > } > > /* /<entry> */ > @@ -651,6 +665,9 @@ static ssize_t bm_entry_write(struct file *file, const char __user *buffer, > struct dentry *root; > Node *e = file_inode(file)->i_private; > int res = parse_command(buffer, count); > + struct binfmt_namespace *ns; > + > + ns = binfmt_ns(file->f_path.dentry->d_sb->s_user_ns); > > switch (res) { > case 1: > @@ -667,7 +684,7 @@ static ssize_t bm_entry_write(struct file *file, const char __user *buffer, > inode_lock(d_inode(root)); > > if (!list_empty(&e->list)) > - kill_node(e); > + kill_node(ns, e); > > inode_unlock(d_inode(root)); > break; > @@ -693,6 +710,7 @@ static ssize_t bm_register_write(struct file *file, const char __user *buffer, > struct inode *inode; > struct super_block *sb = file_inode(file)->i_sb; > struct dentry *root = sb->s_root, *dentry; > + struct binfmt_namespace *ns; > int err = 0; > > e = create_entry(buffer, count); > @@ -716,7 +734,9 @@ static ssize_t bm_register_write(struct file *file, const char __user *buffer, > if (!inode) > goto out2; > > - err = simple_pin_fs(&bm_fs_type, &bm_mnt, &entry_count); > + ns = binfmt_ns(file->f_path.dentry->d_sb->s_user_ns); > + err = simple_pin_fs(&bm_fs_type, &ns->bm_mnt, > + &ns->entry_count); > if (err) { > iput(inode); > inode = NULL; > @@ -725,12 +745,16 @@ static ssize_t bm_register_write(struct file *file, const char __user *buffer, > > if (e->flags & MISC_FMT_OPEN_FILE) { > struct file *f; > + const struct cred *old_cred; > > + old_cred = override_creds(file->f_cred); > f = open_exec(e->interpreter); > + revert_creds(old_cred); > if (IS_ERR(f)) { > err = PTR_ERR(f); > pr_notice("register: failed to install interpreter file %s\n", e->interpreter); > - simple_release_fs(&bm_mnt, &entry_count); > + simple_release_fs(&ns->bm_mnt, > + &ns->entry_count); > iput(inode); > inode = NULL; > goto out2; > @@ -743,9 +767,9 @@ static ssize_t bm_register_write(struct file *file, const char __user *buffer, > inode->i_fop = &bm_entry_operations; > > d_instantiate(dentry, inode); > - write_lock(&entries_lock); > - list_add(&e->list, &entries); > - write_unlock(&entries_lock); > + write_lock(&ns->entries_lock); > + list_add(&e->list, &ns->entries); > + write_unlock(&ns->entries_lock); > > err = 0; > out2: > @@ -770,7 +794,9 @@ static const struct file_operations bm_register_operations = { > static ssize_t > bm_status_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos) > { > - char *s = enabled ? "enabled\n" : "disabled\n"; > + struct binfmt_namespace *ns = > + binfmt_ns(file->f_path.dentry->d_sb->s_user_ns); > + char *s = ns->enabled ? "enabled\n" : "disabled\n"; > > return simple_read_from_buffer(buf, nbytes, ppos, s, strlen(s)); > } > @@ -778,25 +804,28 @@ bm_status_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos) > static ssize_t bm_status_write(struct file *file, const char __user *buffer, > size_t count, loff_t *ppos) > { > + struct binfmt_namespace *ns; > int res = parse_command(buffer, count); > struct dentry *root; > > + ns = binfmt_ns(file->f_path.dentry->d_sb->s_user_ns); > switch (res) { > case 1: > /* Disable all handlers. */ > - enabled = 0; > + ns->enabled = 0; > break; > case 2: > /* Enable all handlers. */ > - enabled = 1; > + ns->enabled = 1; > break; > case 3: > /* Delete all handlers. */ > root = file_inode(file)->i_sb->s_root; > inode_lock(d_inode(root)); > > - while (!list_empty(&entries)) > - kill_node(list_first_entry(&entries, Node, list)); > + while (!list_empty(&ns->entries)) > + kill_node(ns, list_first_entry(&ns->entries, > + Node, list)); > > inode_unlock(d_inode(root)); > break; > @@ -823,12 +852,34 @@ static const struct super_operations s_ops = { > static int bm_fill_super(struct super_block *sb, void *data, int silent) > { > int err; > + struct user_namespace *ns = sb->s_user_ns; > static const struct tree_descr bm_files[] = { > [2] = {"status", &bm_status_operations, S_IWUSR|S_IRUGO}, > [3] = {"register", &bm_register_operations, S_IWUSR}, > /* last one */ {""} > }; > > + /* create a new binfmt namespace > + * if we are not in the first user namespace > + * but the binfmt namespace is the first one > + */ > + if (READ_ONCE(ns->binfmt_ns) == NULL) { > + struct binfmt_namespace *new_ns; > + > + new_ns = kmalloc(sizeof(struct binfmt_namespace), > + GFP_KERNEL); > + if (new_ns == NULL) > + return -ENOMEM; > + INIT_LIST_HEAD(&new_ns->entries); > + new_ns->enabled = 1; > + rwlock_init(&new_ns->entries_lock); > + new_ns->bm_mnt = NULL; > + new_ns->entry_count = 0; > + /* ensure new_ns is completely initialized before sharing it */ > + smp_wmb(); > + WRITE_ONCE(ns->binfmt_ns, new_ns); > + } > + > err = simple_fill_super(sb, BINFMTFS_MAGIC, bm_files); > if (!err) > sb->s_op = &s_ops; > @@ -838,7 +889,10 @@ static int bm_fill_super(struct super_block *sb, void *data, int silent) > static struct dentry *bm_mount(struct file_system_type *fs_type, > int flags, const char *dev_name, void *data) > { > - return mount_single(fs_type, flags, data, bm_fill_super); > + struct user_namespace *ns = current_user_ns(); > + > + return mount_ns(fs_type, flags, data, ns, ns, > + bm_fill_super); > } > > static struct linux_binfmt misc_format = { > @@ -849,6 +903,7 @@ static struct linux_binfmt misc_format = { > static struct file_system_type bm_fs_type = { > .owner = THIS_MODULE, > .name = "binfmt_misc", > + .fs_flags = FS_USERNS_MOUNT, > .mount = bm_mount, > .kill_sb = kill_litter_super, > }; > diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h > index d6b74b91096b..319141da5315 100644 > --- a/include/linux/user_namespace.h > +++ b/include/linux/user_namespace.h > @@ -52,6 +52,18 @@ enum ucount_type { > UCOUNT_COUNTS, > }; > > +#if IS_ENABLED(CONFIG_BINFMT_MISC) > +struct binfmt_namespace { > + struct list_head entries; > + rwlock_t entries_lock; > + int enabled; > + struct vfsmount *bm_mnt; > + int entry_count; > +} __randomize_layout; > + > +extern struct binfmt_namespace init_binfmt_ns; > +#endif > + > struct user_namespace { > struct uid_gid_map uid_map; > struct uid_gid_map gid_map; > @@ -76,6 +88,9 @@ struct user_namespace { > #endif > struct ucounts *ucounts; > int ucount_max[UCOUNT_COUNTS]; > +#if IS_ENABLED(CONFIG_BINFMT_MISC) > + struct binfmt_namespace *binfmt_ns; > +#endif > } __randomize_layout; > > struct ucounts { > diff --git a/kernel/user.c b/kernel/user.c > index 0df9b1640b2a..220ab2053d44 100644 > --- a/kernel/user.c > +++ b/kernel/user.c > @@ -19,6 +19,17 @@ > #include <linux/user_namespace.h> > #include <linux/proc_ns.h> > > +#if IS_ENABLED(CONFIG_BINFMT_MISC) > +struct binfmt_namespace init_binfmt_ns = { > + .entries = LIST_HEAD_INIT(init_binfmt_ns.entries), > + .enabled = 1, > + .entries_lock = __RW_LOCK_UNLOCKED(init_binfmt_ns.entries_lock), > + .bm_mnt = NULL, > + .entry_count = 0, > +}; > +EXPORT_SYMBOL_GPL(init_binfmt_ns); > +#endif > + > /* > * userns count is 1 for root user, 1 for init_uts_ns, > * and 1 for... ? > @@ -66,6 +77,9 @@ struct user_namespace init_user_ns = { > .persistent_keyring_register_sem = > __RWSEM_INITIALIZER(init_user_ns.persistent_keyring_register_sem), > #endif > +#if IS_ENABLED(CONFIG_BINFMT_MISC) > + .binfmt_ns = &init_binfmt_ns, > +#endif > }; > EXPORT_SYMBOL_GPL(init_user_ns); > > diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c > index e5222b5fb4fe..990cf5950a89 100644 > --- a/kernel/user_namespace.c > +++ b/kernel/user_namespace.c > @@ -195,6 +195,9 @@ static void free_user_ns(struct work_struct *work) > kfree(ns->projid_map.forward); > kfree(ns->projid_map.reverse); > } > +#if IS_ENABLED(CONFIG_BINFMT_MISC) > + kfree(ns->binfmt_ns); > +#endif > retire_userns_sysctls(ns); > #ifdef CONFIG_PERSISTENT_KEYRINGS > key_put(ns->persistent_keyring_register); > -- > 2.17.1 >
On 16/10/2018 17:22, Andrei Vagin wrote: > On Wed, Oct 10, 2018 at 06:14:30PM +0200, Laurent Vivier wrote: >> This patch allows to have a different binfmt_misc configuration >> for each new user namespace. By default, the binfmt_misc configuration >> is the one of the previous level, but if the binfmt_misc filesystem is >> mounted in the new namespace a new empty binfmt instance is created and >> used in this namespace. >> >> For instance, using "unshare" we can start a chroot of another >> architecture and configure the binfmt_misc interpreter without being root >> to run the binaries in this chroot. >> >> Signed-off-by: Laurent Vivier <laurent@vivier.eu> > > Acked-by: Andrei Vagin <avagin@gmail.com> > > Thanks, > Andrei > I don't konw who is the maintainer for this part, but is there any chance to have this merged in 4.20? Thanks, Laurent
Le 24/10/2018 à 19:15, Laurent Vivier a écrit : > On 16/10/2018 17:22, Andrei Vagin wrote: >> On Wed, Oct 10, 2018 at 06:14:30PM +0200, Laurent Vivier wrote: >>> This patch allows to have a different binfmt_misc configuration >>> for each new user namespace. By default, the binfmt_misc configuration >>> is the one of the previous level, but if the binfmt_misc filesystem is >>> mounted in the new namespace a new empty binfmt instance is created and >>> used in this namespace. >>> >>> For instance, using "unshare" we can start a chroot of another >>> architecture and configure the binfmt_misc interpreter without being root >>> to run the binaries in this chroot. >>> >>> Signed-off-by: Laurent Vivier <laurent@vivier.eu> >> >> Acked-by: Andrei Vagin <avagin@gmail.com> >> >> Thanks, >> Andrei >> > > I don't konw who is the maintainer for this part, but is there any > chance to have this merged in 4.20? > I'd really want to have this merged. I have some real use cases for this: 1- to allow a non root user to run a container (with "unshare" for instance) with its own binfmt_misc configuration. For instance, like we provide a disk image and ask an ordinary user to run it with his favorite VM hypervisor, we can provide a tar.gz containing our own interpreter and just ask him to unshare+chroot to the exploded file tree, 2- to allow to run automatic tests of an interpreter on a machine without having to change the global configuration of the system. I have in mind to add some tests in Avocado to automatically test qemu-linux-user in containers, so the interpreter path can depend on the build path and possibly run them concurrently, 3- to select an interpreter by container. For instance, on the qemu-devel mailing list, we have a waiting patch to add the bFLT interpreter binfmt_misc configuration, but the bFLT doesn't provide the CPU type in magic/mask. So it would be interesting to be able to select also a bFLT interpreter by container, as we know the CPU architecture we have in each chroot/container, 4- another example to select an interpreter by container is qemu-mips and qemu-misn32 share the same magic/mask because only the kernel API changes, so we can't configure both on the system (but I agree it's a QEMU bug: they should be merged and the kernel API be selected at runtime). Thanks, Laurent
On Tue, Oct 30, 2018 at 9:51 AM Laurent Vivier <laurent@vivier.eu> wrote: > Le 24/10/2018 à 19:15, Laurent Vivier a écrit : > > On 16/10/2018 17:22, Andrei Vagin wrote: > >> On Wed, Oct 10, 2018 at 06:14:30PM +0200, Laurent Vivier wrote: > >>> This patch allows to have a different binfmt_misc configuration > >>> for each new user namespace. By default, the binfmt_misc configuration > >>> is the one of the previous level, but if the binfmt_misc filesystem is > >>> mounted in the new namespace a new empty binfmt instance is created and > >>> used in this namespace. > >>> > >>> For instance, using "unshare" we can start a chroot of another > >>> architecture and configure the binfmt_misc interpreter without being root > >>> to run the binaries in this chroot. > >>> > >>> Signed-off-by: Laurent Vivier <laurent@vivier.eu> > >> > >> Acked-by: Andrei Vagin <avagin@gmail.com> > >> > >> Thanks, > >> Andrei > >> > > > > I don't konw who is the maintainer for this part, I think Andrew Morton is the right maintainer here. > > but is there any > > chance to have this merged in 4.20? > > > > I'd really want to have this merged. > > I have some real use cases for this: > > 1- to allow a non root user to run a container (with "unshare" for > instance) with its own binfmt_misc configuration. For instance, like we > provide a disk image and ask an ordinary user to run it with his > favorite VM hypervisor, we can provide a tar.gz containing our own > interpreter and just ask him to unshare+chroot to the exploded file tree, > > 2- to allow to run automatic tests of an interpreter on a machine > without having to change the global configuration of the system. I have > in mind to add some tests in Avocado to automatically test > qemu-linux-user in containers, so the interpreter path can depend on the > build path and possibly run them concurrently, > > 3- to select an interpreter by container. For instance, on the > qemu-devel mailing list, we have a waiting patch to add the bFLT > interpreter binfmt_misc configuration, but the bFLT doesn't provide the > CPU type in magic/mask. So it would be interesting to be able to select > also a bFLT interpreter by container, as we know the CPU architecture we > have in each chroot/container, > > 4- another example to select an interpreter by container is qemu-mips > and qemu-misn32 share the same magic/mask because only the kernel API > changes, so we can't configure both on the system (but I agree it's a > QEMU bug: they should be merged and the kernel API be selected at runtime).
diff --git a/fs/binfmt_misc.c b/fs/binfmt_misc.c index aa4a7a23ff99..df9dc3248b7b 100644 --- a/fs/binfmt_misc.c +++ b/fs/binfmt_misc.c @@ -38,9 +38,6 @@ enum { VERBOSE_STATUS = 1 /* make it zero to save 400 bytes kernel memory */ }; -static LIST_HEAD(entries); -static int enabled = 1; - enum {Enabled, Magic}; #define MISC_FMT_PRESERVE_ARGV0 (1 << 31) #define MISC_FMT_OPEN_BINARY (1 << 30) @@ -60,10 +57,7 @@ typedef struct { struct file *interp_file; } Node; -static DEFINE_RWLOCK(entries_lock); static struct file_system_type bm_fs_type; -static struct vfsmount *bm_mnt; -static int entry_count; /* * Max length of the register string. Determined by: @@ -80,18 +74,37 @@ static int entry_count; */ #define MAX_REGISTER_LENGTH 1920 +static struct binfmt_namespace *binfmt_ns(struct user_namespace *ns) +{ + struct binfmt_namespace *b_ns; + + while (ns) { + b_ns = READ_ONCE(ns->binfmt_ns); + if (b_ns) + return b_ns; + ns = ns->parent; + } + /* as the first user namespace is initialized with + * &init_binfmt_ns we should never come here + * but we try to stay safe by logging a warning + * and returning a sane value + */ + WARN_ON_ONCE(1); + return &init_binfmt_ns; +} + /* * Check if we support the binfmt * if we do, return the node, else NULL * locking is done in load_misc_binary */ -static Node *check_file(struct linux_binprm *bprm) +static Node *check_file(struct binfmt_namespace *ns, struct linux_binprm *bprm) { char *p = strrchr(bprm->interp, '.'); struct list_head *l; /* Walk all the registered handlers. */ - list_for_each(l, &entries) { + list_for_each(l, &ns->entries) { Node *e = list_entry(l, Node, list); char *s; int j; @@ -133,17 +146,18 @@ static int load_misc_binary(struct linux_binprm *bprm) struct file *interp_file = NULL; int retval; int fd_binary = -1; + struct binfmt_namespace *ns = binfmt_ns(current_user_ns()); retval = -ENOEXEC; - if (!enabled) + if (!ns->enabled) return retval; /* to keep locking time low, we copy the interpreter string */ - read_lock(&entries_lock); - fmt = check_file(bprm); + read_lock(&ns->entries_lock); + fmt = check_file(ns, bprm); if (fmt) dget(fmt->dentry); - read_unlock(&entries_lock); + read_unlock(&ns->entries_lock); if (!fmt) return retval; @@ -609,19 +623,19 @@ static void bm_evict_inode(struct inode *inode) kfree(e); } -static void kill_node(Node *e) +static void kill_node(struct binfmt_namespace *ns, Node *e) { struct dentry *dentry; - write_lock(&entries_lock); + write_lock(&ns->entries_lock); list_del_init(&e->list); - write_unlock(&entries_lock); + write_unlock(&ns->entries_lock); dentry = e->dentry; drop_nlink(d_inode(dentry)); d_drop(dentry); dput(dentry); - simple_release_fs(&bm_mnt, &entry_count); + simple_release_fs(&ns->bm_mnt, &ns->entry_count); } /* /<entry> */ @@ -651,6 +665,9 @@ static ssize_t bm_entry_write(struct file *file, const char __user *buffer, struct dentry *root; Node *e = file_inode(file)->i_private; int res = parse_command(buffer, count); + struct binfmt_namespace *ns; + + ns = binfmt_ns(file->f_path.dentry->d_sb->s_user_ns); switch (res) { case 1: @@ -667,7 +684,7 @@ static ssize_t bm_entry_write(struct file *file, const char __user *buffer, inode_lock(d_inode(root)); if (!list_empty(&e->list)) - kill_node(e); + kill_node(ns, e); inode_unlock(d_inode(root)); break; @@ -693,6 +710,7 @@ static ssize_t bm_register_write(struct file *file, const char __user *buffer, struct inode *inode; struct super_block *sb = file_inode(file)->i_sb; struct dentry *root = sb->s_root, *dentry; + struct binfmt_namespace *ns; int err = 0; e = create_entry(buffer, count); @@ -716,7 +734,9 @@ static ssize_t bm_register_write(struct file *file, const char __user *buffer, if (!inode) goto out2; - err = simple_pin_fs(&bm_fs_type, &bm_mnt, &entry_count); + ns = binfmt_ns(file->f_path.dentry->d_sb->s_user_ns); + err = simple_pin_fs(&bm_fs_type, &ns->bm_mnt, + &ns->entry_count); if (err) { iput(inode); inode = NULL; @@ -725,12 +745,16 @@ static ssize_t bm_register_write(struct file *file, const char __user *buffer, if (e->flags & MISC_FMT_OPEN_FILE) { struct file *f; + const struct cred *old_cred; + old_cred = override_creds(file->f_cred); f = open_exec(e->interpreter); + revert_creds(old_cred); if (IS_ERR(f)) { err = PTR_ERR(f); pr_notice("register: failed to install interpreter file %s\n", e->interpreter); - simple_release_fs(&bm_mnt, &entry_count); + simple_release_fs(&ns->bm_mnt, + &ns->entry_count); iput(inode); inode = NULL; goto out2; @@ -743,9 +767,9 @@ static ssize_t bm_register_write(struct file *file, const char __user *buffer, inode->i_fop = &bm_entry_operations; d_instantiate(dentry, inode); - write_lock(&entries_lock); - list_add(&e->list, &entries); - write_unlock(&entries_lock); + write_lock(&ns->entries_lock); + list_add(&e->list, &ns->entries); + write_unlock(&ns->entries_lock); err = 0; out2: @@ -770,7 +794,9 @@ static const struct file_operations bm_register_operations = { static ssize_t bm_status_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos) { - char *s = enabled ? "enabled\n" : "disabled\n"; + struct binfmt_namespace *ns = + binfmt_ns(file->f_path.dentry->d_sb->s_user_ns); + char *s = ns->enabled ? "enabled\n" : "disabled\n"; return simple_read_from_buffer(buf, nbytes, ppos, s, strlen(s)); } @@ -778,25 +804,28 @@ bm_status_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos) static ssize_t bm_status_write(struct file *file, const char __user *buffer, size_t count, loff_t *ppos) { + struct binfmt_namespace *ns; int res = parse_command(buffer, count); struct dentry *root; + ns = binfmt_ns(file->f_path.dentry->d_sb->s_user_ns); switch (res) { case 1: /* Disable all handlers. */ - enabled = 0; + ns->enabled = 0; break; case 2: /* Enable all handlers. */ - enabled = 1; + ns->enabled = 1; break; case 3: /* Delete all handlers. */ root = file_inode(file)->i_sb->s_root; inode_lock(d_inode(root)); - while (!list_empty(&entries)) - kill_node(list_first_entry(&entries, Node, list)); + while (!list_empty(&ns->entries)) + kill_node(ns, list_first_entry(&ns->entries, + Node, list)); inode_unlock(d_inode(root)); break; @@ -823,12 +852,34 @@ static const struct super_operations s_ops = { static int bm_fill_super(struct super_block *sb, void *data, int silent) { int err; + struct user_namespace *ns = sb->s_user_ns; static const struct tree_descr bm_files[] = { [2] = {"status", &bm_status_operations, S_IWUSR|S_IRUGO}, [3] = {"register", &bm_register_operations, S_IWUSR}, /* last one */ {""} }; + /* create a new binfmt namespace + * if we are not in the first user namespace + * but the binfmt namespace is the first one + */ + if (READ_ONCE(ns->binfmt_ns) == NULL) { + struct binfmt_namespace *new_ns; + + new_ns = kmalloc(sizeof(struct binfmt_namespace), + GFP_KERNEL); + if (new_ns == NULL) + return -ENOMEM; + INIT_LIST_HEAD(&new_ns->entries); + new_ns->enabled = 1; + rwlock_init(&new_ns->entries_lock); + new_ns->bm_mnt = NULL; + new_ns->entry_count = 0; + /* ensure new_ns is completely initialized before sharing it */ + smp_wmb(); + WRITE_ONCE(ns->binfmt_ns, new_ns); + } + err = simple_fill_super(sb, BINFMTFS_MAGIC, bm_files); if (!err) sb->s_op = &s_ops; @@ -838,7 +889,10 @@ static int bm_fill_super(struct super_block *sb, void *data, int silent) static struct dentry *bm_mount(struct file_system_type *fs_type, int flags, const char *dev_name, void *data) { - return mount_single(fs_type, flags, data, bm_fill_super); + struct user_namespace *ns = current_user_ns(); + + return mount_ns(fs_type, flags, data, ns, ns, + bm_fill_super); } static struct linux_binfmt misc_format = { @@ -849,6 +903,7 @@ static struct linux_binfmt misc_format = { static struct file_system_type bm_fs_type = { .owner = THIS_MODULE, .name = "binfmt_misc", + .fs_flags = FS_USERNS_MOUNT, .mount = bm_mount, .kill_sb = kill_litter_super, }; diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h index d6b74b91096b..319141da5315 100644 --- a/include/linux/user_namespace.h +++ b/include/linux/user_namespace.h @@ -52,6 +52,18 @@ enum ucount_type { UCOUNT_COUNTS, }; +#if IS_ENABLED(CONFIG_BINFMT_MISC) +struct binfmt_namespace { + struct list_head entries; + rwlock_t entries_lock; + int enabled; + struct vfsmount *bm_mnt; + int entry_count; +} __randomize_layout; + +extern struct binfmt_namespace init_binfmt_ns; +#endif + struct user_namespace { struct uid_gid_map uid_map; struct uid_gid_map gid_map; @@ -76,6 +88,9 @@ struct user_namespace { #endif struct ucounts *ucounts; int ucount_max[UCOUNT_COUNTS]; +#if IS_ENABLED(CONFIG_BINFMT_MISC) + struct binfmt_namespace *binfmt_ns; +#endif } __randomize_layout; struct ucounts { diff --git a/kernel/user.c b/kernel/user.c index 0df9b1640b2a..220ab2053d44 100644 --- a/kernel/user.c +++ b/kernel/user.c @@ -19,6 +19,17 @@ #include <linux/user_namespace.h> #include <linux/proc_ns.h> +#if IS_ENABLED(CONFIG_BINFMT_MISC) +struct binfmt_namespace init_binfmt_ns = { + .entries = LIST_HEAD_INIT(init_binfmt_ns.entries), + .enabled = 1, + .entries_lock = __RW_LOCK_UNLOCKED(init_binfmt_ns.entries_lock), + .bm_mnt = NULL, + .entry_count = 0, +}; +EXPORT_SYMBOL_GPL(init_binfmt_ns); +#endif + /* * userns count is 1 for root user, 1 for init_uts_ns, * and 1 for... ? @@ -66,6 +77,9 @@ struct user_namespace init_user_ns = { .persistent_keyring_register_sem = __RWSEM_INITIALIZER(init_user_ns.persistent_keyring_register_sem), #endif +#if IS_ENABLED(CONFIG_BINFMT_MISC) + .binfmt_ns = &init_binfmt_ns, +#endif }; EXPORT_SYMBOL_GPL(init_user_ns); diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c index e5222b5fb4fe..990cf5950a89 100644 --- a/kernel/user_namespace.c +++ b/kernel/user_namespace.c @@ -195,6 +195,9 @@ static void free_user_ns(struct work_struct *work) kfree(ns->projid_map.forward); kfree(ns->projid_map.reverse); } +#if IS_ENABLED(CONFIG_BINFMT_MISC) + kfree(ns->binfmt_ns); +#endif retire_userns_sysctls(ns); #ifdef CONFIG_PERSISTENT_KEYRINGS key_put(ns->persistent_keyring_register);
This patch allows to have a different binfmt_misc configuration for each new user namespace. By default, the binfmt_misc configuration is the one of the previous level, but if the binfmt_misc filesystem is mounted in the new namespace a new empty binfmt instance is created and used in this namespace. For instance, using "unshare" we can start a chroot of another architecture and configure the binfmt_misc interpreter without being root to run the binaries in this chroot. Signed-off-by: Laurent Vivier <laurent@vivier.eu> --- fs/binfmt_misc.c | 111 ++++++++++++++++++++++++--------- include/linux/user_namespace.h | 15 +++++ kernel/user.c | 14 +++++ kernel/user_namespace.c | 3 + 4 files changed, 115 insertions(+), 28 deletions(-)