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Commit 2db154b3 authored by David Howells's avatar David Howells Committed by Al Viro
Browse files

vfs: syscall: Add move_mount(2) to move mounts around 



Add a move_mount() system call that will move a mount from one place to
another and, in the next commit, allow to attach an unattached mount tree.

The new system call looks like the following:

	int move_mount(int from_dfd, const char *from_path,
		       int to_dfd, const char *to_path,
		       unsigned int flags);

Signed-off-by: default avatarDavid Howells <dhowells@redhat.com>
cc: linux-api@vger.kernel.org
Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent a07b2000

arch/x86/entry/syscalls/syscall_32.tbl

+2 −1
Original line number Diff line number Diff line
@@ -399,7 +399,8 @@ 
385	i386	io_pgetevents		sys_io_pgetevents_time32	__ia32_compat_sys_io_pgetevents

386	i386	rseq			sys_rseq			__ia32_sys_rseq

387	i386	open_tree		sys_open_tree			__ia32_sys_open_tree

# don't use numbers 388 through 392, add new calls at the end

388	i386	move_mount		sys_move_mount			__ia32_sys_move_mount

# don't use numbers 389 through 392, add new calls at the end

393	i386	semget			sys_semget    			__ia32_sys_semget

394	i386	semctl			sys_semctl    			__ia32_compat_sys_semctl

395	i386	shmget			sys_shmget    			__ia32_sys_shmget

arch/x86/entry/syscalls/syscall_64.tbl

+1 −0
Original line number Diff line number Diff line
@@ -344,6 +344,7 @@ 
333	common	io_pgetevents		__x64_sys_io_pgetevents

334	common	rseq			__x64_sys_rseq

335	common	open_tree		__x64_sys_open_tree

336	common	move_mount		__x64_sys_move_mount

# don't use numbers 387 through 423, add new calls after the last

# 'common' entry

424	common	pidfd_send_signal	__x64_sys_pidfd_send_signal

fs/namespace.c

+95 −31
Original line number Diff line number Diff line
@@ -2539,72 +2539,81 @@ static inline int tree_contains_unbindable(struct mount *mnt) 
	return 0;

}



static int do_move_mount(struct path *path, const char *old_name)

static int do_move_mount(struct path *old_path, struct path *new_path)

{

	struct path old_path, parent_path;

	struct path parent_path = {.mnt = NULL, .dentry = NULL};

	struct mount *p;

	struct mount *old;

	struct mountpoint *mp;

	int err;

	if (!old_name || !*old_name)

		return -EINVAL;

	err = kern_path(old_name, LOOKUP_FOLLOW, &old_path);

	if (err)

		return err;



	mp = lock_mount(path);

	err = PTR_ERR(mp);

	mp = lock_mount(new_path);

	if (IS_ERR(mp))

		goto out;

		return PTR_ERR(mp);



	old = real_mount(old_path.mnt);

	p = real_mount(path->mnt);

	old = real_mount(old_path->mnt);

	p = real_mount(new_path->mnt);



	err = -EINVAL;

	if (!check_mnt(p) || !check_mnt(old))

		goto out1;

		goto out;



	if (old->mnt.mnt_flags & MNT_LOCKED)

		goto out1;

	if (!mnt_has_parent(old))

		goto out;



	err = -EINVAL;

	if (old_path.dentry != old_path.mnt->mnt_root)

		goto out1;

	if (old->mnt.mnt_flags & MNT_LOCKED)

		goto out;



	if (!mnt_has_parent(old))

		goto out1;

	if (old_path->dentry != old_path->mnt->mnt_root)

		goto out;



	if (d_is_dir(path->dentry) !=

	      d_is_dir(old_path.dentry))

		goto out1;

	if (d_is_dir(new_path->dentry) !=

	    d_is_dir(old_path->dentry))

		goto out;

	/*

	 * Don't move a mount residing in a shared parent.

	 */

	if (IS_MNT_SHARED(old->mnt_parent))

		goto out1;

		goto out;

	/*

	 * Don't move a mount tree containing unbindable mounts to a destination

	 * mount which is shared.

	 */

	if (IS_MNT_SHARED(p) && tree_contains_unbindable(old))

		goto out1;

		goto out;

	err = -ELOOP;

	for (; mnt_has_parent(p); p = p->mnt_parent)

		if (p == old)

			goto out1;

			goto out;



	err = attach_recursive_mnt(old, real_mount(path->mnt), mp, &parent_path);

	err = attach_recursive_mnt(old, real_mount(new_path->mnt), mp,

				   &parent_path);

	if (err)

		goto out1;

		goto out;



	/* if the mount is moved, it should no longer be expire

	 * automatically */

	list_del_init(&old->mnt_expire);

out1:

	unlock_mount(mp);

out:

	unlock_mount(mp);

	if (!err)

		path_put(&parent_path);

	return err;

}



static int do_move_mount_old(struct path *path, const char *old_name)

{

	struct path old_path;

	int err;



	if (!old_name || !*old_name)

		return -EINVAL;



	err = kern_path(old_name, LOOKUP_FOLLOW, &old_path);

	if (err)

		return err;



	err = do_move_mount(&old_path, path);

	path_put(&old_path);

	return err;

}
@@ -3050,7 +3059,7 @@ long do_mount(const char *dev_name, const char __user *dir_name, 
	else if (flags & (MS_SHARED | MS_PRIVATE | MS_SLAVE | MS_UNBINDABLE))

		retval = do_change_type(&path, flags);

	else if (flags & MS_MOVE)

		retval = do_move_mount(&path, dev_name);

		retval = do_move_mount_old(&path, dev_name);

	else

		retval = do_new_mount(&path, type_page, sb_flags, mnt_flags,

				      dev_name, data_page);
@@ -3278,6 +3287,61 @@ SYSCALL_DEFINE5(mount, char __user *, dev_name, char __user *, dir_name, 
	return ksys_mount(dev_name, dir_name, type, flags, data);

}



/*

 * Move a mount from one place to another.

 *

 * Note the flags value is a combination of MOVE_MOUNT_* flags.

 */

SYSCALL_DEFINE5(move_mount,

		int, from_dfd, const char *, from_pathname,

		int, to_dfd, const char *, to_pathname,

		unsigned int, flags)

{

	struct path from_path, to_path;

	unsigned int lflags;

	int ret = 0;



	if (!may_mount())

		return -EPERM;



	if (flags & ~MOVE_MOUNT__MASK)

		return -EINVAL;



	/* If someone gives a pathname, they aren't permitted to move

	 * from an fd that requires unmount as we can't get at the flag

	 * to clear it afterwards.

	 */

	lflags = 0;

	if (flags & MOVE_MOUNT_F_SYMLINKS)	lflags |= LOOKUP_FOLLOW;

	if (flags & MOVE_MOUNT_F_AUTOMOUNTS)	lflags |= LOOKUP_AUTOMOUNT;

	if (flags & MOVE_MOUNT_F_EMPTY_PATH)	lflags |= LOOKUP_EMPTY;



	ret = user_path_at(from_dfd, from_pathname, lflags, &from_path);

	if (ret < 0)

		return ret;



	lflags = 0;

	if (flags & MOVE_MOUNT_T_SYMLINKS)	lflags |= LOOKUP_FOLLOW;

	if (flags & MOVE_MOUNT_T_AUTOMOUNTS)	lflags |= LOOKUP_AUTOMOUNT;

	if (flags & MOVE_MOUNT_T_EMPTY_PATH)	lflags |= LOOKUP_EMPTY;



	ret = user_path_at(to_dfd, to_pathname, lflags, &to_path);

	if (ret < 0)

		goto out_from;



	ret = security_move_mount(&from_path, &to_path);

	if (ret < 0)

		goto out_to;



	ret = do_move_mount(&from_path, &to_path);



out_to:

	path_put(&to_path);

out_from:

	path_put(&from_path);

	return ret;

}



/*

 * Return true if path is reachable from root

 *

include/linux/lsm_hooks.h

+6 −0
Original line number Diff line number Diff line
@@ -160,6 +160,10 @@ 
 *	Parse a string of security data filling in the opts structure

 *	@options string containing all mount options known by the LSM

 *	@opts binary data structure usable by the LSM

 * @move_mount:

 *	Check permission before a mount is moved.

 *	@from_path indicates the mount that is going to be moved.

 *	@to_path indicates the mountpoint that will be mounted upon.

 * @dentry_init_security:

 *	Compute a context for a dentry as the inode is not yet available

 *	since NFSv4 has no label backed by an EA anyway.
@@ -1501,6 +1505,7 @@ union security_list_options { 
					unsigned long *set_kern_flags);

	int (*sb_add_mnt_opt)(const char *option, const char *val, int len,

			      void **mnt_opts);

	int (*move_mount)(const struct path *from_path, const struct path *to_path);

	int (*dentry_init_security)(struct dentry *dentry, int mode,

					const struct qstr *name, void **ctx,

					u32 *ctxlen);
@@ -1835,6 +1840,7 @@ struct security_hook_heads { 
	struct hlist_head sb_set_mnt_opts;

	struct hlist_head sb_clone_mnt_opts;

	struct hlist_head sb_add_mnt_opt;

	struct hlist_head move_mount;

	struct hlist_head dentry_init_security;

	struct hlist_head dentry_create_files_as;

#ifdef CONFIG_SECURITY_PATH

include/linux/security.h

+7 −0
Original line number Diff line number Diff line
@@ -250,6 +250,7 @@ int security_sb_clone_mnt_opts(const struct super_block *oldsb, 
				unsigned long *set_kern_flags);

int security_add_mnt_opt(const char *option, const char *val,

				int len, void **mnt_opts);

int security_move_mount(const struct path *from_path, const struct path *to_path);

int security_dentry_init_security(struct dentry *dentry, int mode,

					const struct qstr *name, void **ctx,

					u32 *ctxlen);
@@ -611,6 +612,12 @@ static inline int security_add_mnt_opt(const char *option, const char *val, 
	return 0;

}



static inline int security_move_mount(const struct path *from_path,

				      const struct path *to_path)

{

	return 0;

}



static inline int security_inode_alloc(struct inode *inode)

{

	return 0;