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@xxxxxxxxxx>
cc: linux-api@xxxxxxxxxxxxxxx
Signed-off-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
---
arch/x86/entry/syscalls/syscall_32.tbl | 1
arch/x86/entry/syscalls/syscall_64.tbl | 1
fs/namespace.c | 126
++++++++++++++++++++++++--------
include/linux/lsm_hooks.h | 6 ++
include/linux/security.h | 7 ++
include/linux/syscalls.h | 3 +
include/uapi/linux/mount.h | 11 +++
security/security.c | 5 +
8 files changed, 129 insertions(+), 31 deletions(-)
diff --git a/fs/namespace.c b/fs/namespace.c
index 112d46f26fc3..f10122028a11 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -2537,72 +2537,81 @@ 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.
+ */
