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: David Howells <dhowells@redhat.com>
cc: linux-api@vger.kernel.org
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/arch/x86/entry/syscalls/syscall_32.tbl b/arch/x86/entry/syscalls/syscall_32.tbl
index ae2294d..0db9eff 100644
--- a/arch/x86/entry/syscalls/syscall_32.tbl
+++ b/arch/x86/entry/syscalls/syscall_32.tbl
@@ -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
diff --git a/arch/x86/entry/syscalls/syscall_64.tbl b/arch/x86/entry/syscalls/syscall_64.tbl
index a6e06c3..0440f0e 100644
--- a/arch/x86/entry/syscalls/syscall_64.tbl
+++ b/arch/x86/entry/syscalls/syscall_64.tbl
@@ -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
diff --git a/fs/namespace.c b/fs/namespace.c
index b804a1a..dc600f5 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -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;
-
- if (old->mnt.mnt_flags & MNT_LOCKED)
- goto out1;
-
- err = -EINVAL;
- if (old_path.dentry != old_path.mnt->mnt_root)
- goto out1;
+ goto out;
if (!mnt_has_parent(old))
- goto out1;
+ goto out;
- if (d_is_dir(path->dentry) !=
- d_is_dir(old_path.dentry))
- goto out1;
+ if (old->mnt.mnt_flags & MNT_LOCKED)
+ goto out;
+
+ if (old_path->dentry != old_path->mnt->mnt_root)
+ goto out;
+
+ 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);
@@ -3279,6 +3288,61 @@ SYSCALL_DEFINE5(mount, char __user *, dev_name, char __user *, dir_name,
}
/*
+ * 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
*
* namespace_sem or mount_lock is held
diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
index a9b8ff5..cb33f81 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -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
diff --git a/include/linux/security.h b/include/linux/security.h
index 49f2685..1f2e06a 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -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;
diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index 6c29d58..84347fc 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -986,6 +986,9 @@ asmlinkage long sys_statx(int dfd, const char __user *path, unsigned flags,
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);
diff --git a/include/uapi/linux/mount.h b/include/uapi/linux/mount.h
index fd7ae2e..3634e06 100644
--- a/include/uapi/linux/mount.h
+++ b/include/uapi/linux/mount.h
@@ -61,4 +61,15 @@
#define OPEN_TREE_CLONE 1 /* Clone the target tree and attach the clone */
#define OPEN_TREE_CLOEXEC O_CLOEXEC /* Close the file on execve() */
+/*
+ * move_mount() flags.
+ */
+#define MOVE_MOUNT_F_SYMLINKS 0x00000001 /* Follow symlinks on from path */
+#define MOVE_MOUNT_F_AUTOMOUNTS 0x00000002 /* Follow automounts on from path */
+#define MOVE_MOUNT_F_EMPTY_PATH 0x00000004 /* Empty from path permitted */
+#define MOVE_MOUNT_T_SYMLINKS 0x00000010 /* Follow symlinks on to path */
+#define MOVE_MOUNT_T_AUTOMOUNTS 0x00000020 /* Follow automounts on to path */
+#define MOVE_MOUNT_T_EMPTY_PATH 0x00000040 /* Empty to path permitted */
+#define MOVE_MOUNT__MASK 0x00000077
+
#endif /* _UAPI_LINUX_MOUNT_H */
diff --git a/security/security.c b/security/security.c
index 23cbb1a..5b3d23e 100644
--- a/security/security.c
+++ b/security/security.c
@@ -866,6 +866,11 @@ int security_add_mnt_opt(const char *option, const char *val, int len,
}
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);