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);

David Howells committed 8 years ago

Commit 2db154b1 parent a07b2008 files · +130 −32Browse files

Unified · Split

8 files

arch/x86/entry/syscalls/syscall_32.tbl +2 −1
arch/x86/entry/syscalls/syscall_64.tbl +1 −0
fs/namespace.c +95 −31
include/linux/lsm_hooks.h +6 −0
include/linux/security.h +7 −0
include/linux/syscalls.h +3 −0
include/uapi/linux/mount.h +11 −0
security/security.c +5 −0

arch/x86/entry/syscalls/syscall_32.tbl+2−1

 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

@@ -344,6 +344,7 @@ · 343 unmodified lines
344	333 common io_pgetevents __x64_sys_io_pgetevents	344	333 common io_pgetevents __x64_sys_io_pgetevents
345	334 common rseq __x64_sys_rseq	345	334 common rseq __x64_sys_rseq
346	335 common open_tree __x64_sys_open_tree	346	335 common open_tree __x64_sys_open_tree
		347	336 common move_mount __x64_sys_move_mount
347	# don't use numbers 387 through 423, add new calls after the last	348	# don't use numbers 387 through 423, add new calls after the last
348	# 'common' entry	349	# 'common' entry
349	424 common pidfd_send_signal __x64_sys_pidfd_send_signal	350	424 common pidfd_send_signal __x64_sys_pidfd_send_signal

fs/namespace.c+95−31

 	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);
+	mp = lock_mount(new_path);
-	err = PTR_ERR(mp);
 	if (IS_ERR(mp))
-		goto out;
+		return PTR_ERR(mp);
-	old = real_mount(old_path.mnt);
+	old = real_mount(old_path->mnt);
-	p = real_mount(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)
+	if (!mnt_has_parent(old))
-		goto out1;
+		goto out;
-	err = -EINVAL;
+	if (old->mnt.mnt_flags & MNT_LOCKED)
-	if (old_path.dentry != old_path.mnt->mnt_root)
+		goto out;
-		goto out1;
-	if (!mnt_has_parent(old))
+	if (old_path->dentry != old_path->mnt->mnt_root)
-		goto out1;
+		goto out;
-	if (d_is_dir(path->dentry) !=
+	if (d_is_dir(new_path->dentry) !=
-	      d_is_dir(old_path.dentry))
+	    d_is_dir(old_path->dentry))
-		goto out1;
+		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;
 }
 	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);
 	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

  *	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.
 					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);
 	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

 				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);
 	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;

include/linux/syscalls.h+3−0

 asmlinkage long sys_rseq(struct rseq __user *rseq, uint32_t rseq_len,
 			 int flags, uint32_t sig);
 asmlinkage long sys_open_tree(int dfd, const char __user *path, unsigned flags);
+asmlinkage long sys_move_mount(int from_dfd, const char __user *from_path,
+			       int to_dfd, const char __user *to_path,
+			       unsigned int ms_flags);
 asmlinkage long sys_pidfd_send_signal(int pidfd, int sig,
 				       siginfo_t __user *info,
 				       unsigned int flags);

include/uapi/linux/mount.h+11−0

@@ -61,4 +61,15 @@ · 60 unmodified lines
61	#define OPEN_TREE_CLONE 1 /* Clone the target tree and attach the clone */	61	#define OPEN_TREE_CLONE 1 /* Clone the target tree and attach the clone */
62	#define OPEN_TREE_CLOEXEC O_CLOEXEC /* Close the file on execve() */	62	#define OPEN_TREE_CLOEXEC O_CLOEXEC /* Close the file on execve() */
63		63
		64	/*
		65	* move_mount() flags.
		66	*/
		67	#define MOVE_MOUNT_F_SYMLINKS 0x00000001 /* Follow symlinks on from path */
		68	#define MOVE_MOUNT_F_AUTOMOUNTS 0x00000002 /* Follow automounts on from path */
		69	#define MOVE_MOUNT_F_EMPTY_PATH 0x00000004 /* Empty from path permitted */
		70	#define MOVE_MOUNT_T_SYMLINKS 0x00000010 /* Follow symlinks on to path */
		71	#define MOVE_MOUNT_T_AUTOMOUNTS 0x00000020 /* Follow automounts on to path */
		72	#define MOVE_MOUNT_T_EMPTY_PATH 0x00000040 /* Empty to path permitted */
		73	#define MOVE_MOUNT__MASK 0x00000077
		74
64	#endif /* _UAPI_LINUX_MOUNT_H */	75	#endif /* _UAPI_LINUX_MOUNT_H */

security/security.c+5−0

 }
 EXPORT_SYMBOL(security_add_mnt_opt);
+int security_move_mount(const struct path *from_path, const struct path *to_path)
+{
+	return call_int_hook(move_mount, 0, from_path, to_path);
+}
 int security_inode_alloc(struct inode *inode)
 {
 	int rc = lsm_inode_alloc(inode);