Commit 0c55cfc4 authored by Eric W. Biederman's avatar Eric W. Biederman
Browse files

vfs: Allow unprivileged manipulation of the mount namespace. 



- Add a filesystem flag to mark filesystems that are safe to mount as
  an unprivileged user.

- Add a filesystem flag to mark filesystems that don't need MNT_NODEV
  when mounted by an unprivileged user.

- Relax the permission checks to allow unprivileged users that have
  CAP_SYS_ADMIN permissions in the user namespace referred to by the
  current mount namespace to be allowed to mount, unmount, and move
  filesystems.

Acked-by: default avatar"Serge E. Hallyn" <serge@hallyn.com>
Signed-off-by: default avatar"Eric W. Biederman" <ebiederm@xmission.com>
parent 7a472ef4

fs/namespace.c

+43 −26
Original line number Diff line number Diff line
@@ -1269,7 +1269,7 @@ SYSCALL_DEFINE2(umount, char __user *, name, int, flags) 
		goto dput_and_out;



	retval = -EPERM;

	if (!capable(CAP_SYS_ADMIN))

	if (!ns_capable(mnt->mnt_ns->user_ns, CAP_SYS_ADMIN))

		goto dput_and_out;



	retval = do_umount(mnt, flags);
@@ -1295,7 +1295,7 @@ SYSCALL_DEFINE1(oldumount, char __user *, name) 


static int mount_is_safe(struct path *path)

{

	if (capable(CAP_SYS_ADMIN))

	if (ns_capable(real_mount(path->mnt)->mnt_ns->user_ns, CAP_SYS_ADMIN))

		return 0;

	return -EPERM;

#ifdef notyet
@@ -1633,7 +1633,7 @@ static int do_change_type(struct path *path, int flag) 
	int type;

	int err = 0;



	if (!capable(CAP_SYS_ADMIN))

	if (!ns_capable(mnt->mnt_ns->user_ns, CAP_SYS_ADMIN))

		return -EPERM;



	if (path->dentry != path->mnt->mnt_root)
@@ -1797,7 +1797,7 @@ static int do_move_mount(struct path *path, const char *old_name) 
	struct mount *p;

	struct mount *old;

	int err = 0;

	if (!capable(CAP_SYS_ADMIN))

	if (!ns_capable(real_mount(path->mnt)->mnt_ns->user_ns, CAP_SYS_ADMIN))

		return -EPERM;

	if (!old_name || !*old_name)

		return -EINVAL;
@@ -1884,21 +1884,6 @@ static struct vfsmount *fs_set_subtype(struct vfsmount *mnt, const char *fstype) 
	return ERR_PTR(err);

}



static struct vfsmount *

do_kern_mount(const char *fstype, int flags, const char *name, void *data)

{

	struct file_system_type *type = get_fs_type(fstype);

	struct vfsmount *mnt;

	if (!type)

		return ERR_PTR(-ENODEV);

	mnt = vfs_kern_mount(type, flags, name, data);

	if (!IS_ERR(mnt) && (type->fs_flags & FS_HAS_SUBTYPE) &&

	    !mnt->mnt_sb->s_subtype)

		mnt = fs_set_subtype(mnt, fstype);

	put_filesystem(type);

	return mnt;

}



/*

 * add a mount into a namespace's mount tree

 */
@@ -1944,20 +1929,46 @@ unlock: 
 * create a new mount for userspace and request it to be added into the

 * namespace's tree

 */

static int do_new_mount(struct path *path, const char *type, int flags,

static int do_new_mount(struct path *path, const char *fstype, int flags,

			int mnt_flags, const char *name, void *data)

{

	struct file_system_type *type;

	struct user_namespace *user_ns;

	struct vfsmount *mnt;

	int err;



	if (!type)

	if (!fstype)

		return -EINVAL;



	/* we need capabilities... */

	if (!capable(CAP_SYS_ADMIN))

	user_ns = real_mount(path->mnt)->mnt_ns->user_ns;

	if (!ns_capable(user_ns, CAP_SYS_ADMIN))

		return -EPERM;



	type = get_fs_type(fstype);

	if (!type)

		return -ENODEV;



	if (user_ns != &init_user_ns) {

		if (!(type->fs_flags & FS_USERNS_MOUNT)) {

			put_filesystem(type);

			return -EPERM;

		}

		/* Only in special cases allow devices from mounts

		 * created outside the initial user namespace.

		 */

		if (!(type->fs_flags & FS_USERNS_DEV_MOUNT)) {

			flags |= MS_NODEV;

			mnt_flags |= MNT_NODEV;

		}

	}



	mnt = do_kern_mount(type, flags, name, data);

	mnt = vfs_kern_mount(type, flags, name, data);

	if (!IS_ERR(mnt) && (type->fs_flags & FS_HAS_SUBTYPE) &&

	    !mnt->mnt_sb->s_subtype)

		mnt = fs_set_subtype(mnt, fstype);



	put_filesystem(type);

	if (IS_ERR(mnt))

		return PTR_ERR(mnt);
@@ -2549,7 +2560,7 @@ SYSCALL_DEFINE2(pivot_root, const char __user *, new_root, 
	struct mount *new_mnt, *root_mnt;

	int error;



	if (!capable(CAP_SYS_ADMIN))

	if (!ns_capable(current->nsproxy->mnt_ns->user_ns, CAP_SYS_ADMIN))

		return -EPERM;



	error = user_path_dir(new_root, &new);
@@ -2631,8 +2642,13 @@ static void __init init_mount_tree(void) 
	struct vfsmount *mnt;

	struct mnt_namespace *ns;

	struct path root;

	struct file_system_type *type;



	mnt = do_kern_mount("rootfs", 0, "rootfs", NULL);

	type = get_fs_type("rootfs");

	if (!type)

		panic("Can't find rootfs type");

	mnt = vfs_kern_mount(type, 0, "rootfs", NULL);

	put_filesystem(type);

	if (IS_ERR(mnt))

		panic("Can't create rootfs");
@@ -2757,7 +2773,8 @@ static int mntns_install(struct nsproxy *nsproxy, void *ns) 
	struct mnt_namespace *mnt_ns = ns;

	struct path root;



	if (!capable(CAP_SYS_ADMIN) || !capable(CAP_SYS_CHROOT))

	if (!ns_capable(mnt_ns->user_ns, CAP_SYS_ADMIN) ||

	    !nsown_capable(CAP_SYS_CHROOT))

		return -EINVAL;



	if (fs->users != 1)

include/linux/fs.h

+2 −0
Original line number Diff line number Diff line
@@ -1812,6 +1812,8 @@ struct file_system_type { 
#define FS_REQUIRES_DEV		1 

#define FS_BINARY_MOUNTDATA	2

#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_REVAL_DOT		16384	/* Check the paths ".", ".." for staleness */

#define FS_RENAME_DOES_D_MOVE	32768	/* FS will handle d_move() during rename() internally. */

	struct dentry *(*mount) (struct file_system_type *, int,

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