| From 1b852bceb0d111e510d1a15826ecc4a19358d512 Mon Sep 17 00:00:00 2001 |
| From: "Eric W. Biederman" <ebiederm@xmission.com> |
| Date: Fri, 8 May 2015 23:22:29 -0500 |
| Subject: mnt: Refactor the logic for mounting sysfs and proc in a user namespace |
| |
| From: "Eric W. Biederman" <ebiederm@xmission.com> |
| |
| commit 1b852bceb0d111e510d1a15826ecc4a19358d512 upstream. |
| |
| Fresh mounts of proc and sysfs are a very special case that works very |
| much like a bind mount. Unfortunately the current structure can not |
| preserve the MNT_LOCK... mount flags. Therefore refactor the logic |
| into a form that can be modified to preserve those lock bits. |
| |
| Add a new filesystem flag FS_USERNS_VISIBLE that requires some mount |
| of the filesystem be fully visible in the current mount namespace, |
| before the filesystem may be mounted. |
| |
| Move the logic for calling fs_fully_visible from proc and sysfs into |
| fs/namespace.c where it has greater access to mount namespace state. |
| |
| Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com> |
| Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| |
| --- |
| fs/namespace.c | 8 +++++++- |
| fs/proc/root.c | 5 +---- |
| fs/sysfs/mount.c | 5 +---- |
| include/linux/fs.h | 2 +- |
| 4 files changed, 10 insertions(+), 10 deletions(-) |
| |
| --- a/fs/namespace.c |
| +++ b/fs/namespace.c |
| @@ -2334,6 +2334,8 @@ unlock: |
| return err; |
| } |
| |
| +static bool fs_fully_visible(struct file_system_type *fs_type); |
| + |
| /* |
| * create a new mount for userspace and request it to be added into the |
| * namespace's tree |
| @@ -2365,6 +2367,10 @@ static int do_new_mount(struct path *pat |
| flags |= MS_NODEV; |
| mnt_flags |= MNT_NODEV | MNT_LOCK_NODEV; |
| } |
| + if (type->fs_flags & FS_USERNS_VISIBLE) { |
| + if (!fs_fully_visible(type)) |
| + return -EPERM; |
| + } |
| } |
| |
| mnt = vfs_kern_mount(type, flags, name, data); |
| @@ -3166,7 +3172,7 @@ bool current_chrooted(void) |
| return chrooted; |
| } |
| |
| -bool fs_fully_visible(struct file_system_type *type) |
| +static bool fs_fully_visible(struct file_system_type *type) |
| { |
| struct mnt_namespace *ns = current->nsproxy->mnt_ns; |
| struct mount *mnt; |
| --- a/fs/proc/root.c |
| +++ b/fs/proc/root.c |
| @@ -112,9 +112,6 @@ static struct dentry *proc_mount(struct |
| ns = task_active_pid_ns(current); |
| options = data; |
| |
| - if (!capable(CAP_SYS_ADMIN) && !fs_fully_visible(fs_type)) |
| - return ERR_PTR(-EPERM); |
| - |
| /* Does the mounter have privilege over the pid namespace? */ |
| if (!ns_capable(ns->user_ns, CAP_SYS_ADMIN)) |
| return ERR_PTR(-EPERM); |
| @@ -159,7 +156,7 @@ static struct file_system_type proc_fs_t |
| .name = "proc", |
| .mount = proc_mount, |
| .kill_sb = proc_kill_sb, |
| - .fs_flags = FS_USERNS_MOUNT, |
| + .fs_flags = FS_USERNS_VISIBLE | FS_USERNS_MOUNT, |
| }; |
| |
| void __init proc_root_init(void) |
| --- a/fs/sysfs/mount.c |
| +++ b/fs/sysfs/mount.c |
| @@ -31,9 +31,6 @@ static struct dentry *sysfs_mount(struct |
| bool new_sb; |
| |
| if (!(flags & MS_KERNMOUNT)) { |
| - if (!capable(CAP_SYS_ADMIN) && !fs_fully_visible(fs_type)) |
| - return ERR_PTR(-EPERM); |
| - |
| if (!kobj_ns_current_may_mount(KOBJ_NS_TYPE_NET)) |
| return ERR_PTR(-EPERM); |
| } |
| @@ -58,7 +55,7 @@ static struct file_system_type sysfs_fs_ |
| .name = "sysfs", |
| .mount = sysfs_mount, |
| .kill_sb = sysfs_kill_sb, |
| - .fs_flags = FS_USERNS_MOUNT, |
| + .fs_flags = FS_USERNS_VISIBLE | FS_USERNS_MOUNT, |
| }; |
| |
| int __init sysfs_init(void) |
| --- a/include/linux/fs.h |
| +++ b/include/linux/fs.h |
| @@ -1863,6 +1863,7 @@ struct file_system_type { |
| #define FS_HAS_SUBTYPE 4 |
| #define FS_USERNS_MOUNT 8 /* Can be mounted by userns root */ |
| #define FS_USERNS_DEV_MOUNT 16 /* A userns mount does not imply MNT_NODEV */ |
| +#define FS_USERNS_VISIBLE 32 /* FS must already be visible */ |
| #define FS_RENAME_DOES_D_MOVE 32768 /* FS will handle d_move() during rename() internally. */ |
| struct dentry *(*mount) (struct file_system_type *, int, |
| const char *, void *); |
| @@ -1950,7 +1951,6 @@ extern int vfs_ustat(dev_t, struct kstat |
| extern int freeze_super(struct super_block *super); |
| extern int thaw_super(struct super_block *super); |
| extern bool our_mnt(struct vfsmount *mnt); |
| -extern bool fs_fully_visible(struct file_system_type *); |
| |
| extern int current_umask(void); |
| |