[PATCH] userns: allow privileged user to operate locked mount

[Gao feng <gaofeng-BthXqXjhjHXQFUHtdCDX3A@public.gmane.org>]

Privileged user should have rights to mount/umount/move
these even locked mount.

Signed-off-by: Gao feng <gaofeng-BthXqXjhjHXQFUHtdCDX3A@public.gmane.org>
---
 fs/namespace.c | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/fs/namespace.c b/fs/namespace.c
index da5c494..7097fc7 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1297,6 +1297,11 @@ static inline bool may_mount(void)
 	return ns_capable(current->nsproxy->mnt_ns->user_ns, CAP_SYS_ADMIN);
 }
 
+static inline bool may_mount_lock(struct mount *mnt)
+{
+	return !(mnt->mnt.mnt_flags & MNT_LOCKED) || capable(CAP_SYS_ADMIN);
+}
+
 /*
  * Now umount can handle mount points as well as block devices.
  * This is important for filesystems which use unnamed block devices.
@@ -1330,7 +1335,7 @@ SYSCALL_DEFINE2(umount, char __user *, name, int, flags)
 		goto dput_and_out;
 	if (!check_mnt(mnt))
 		goto dput_and_out;
-	if (mnt->mnt.mnt_flags & MNT_LOCKED)
+	if (!may_mount_lock(mnt))
 		goto dput_and_out;
 
 	retval = do_umount(mnt, flags);
@@ -1768,7 +1773,8 @@ static int do_loopback(struct path *path, const char *old_name,
 	if (!check_mnt(parent) || !check_mnt(old))
 		goto out2;
 
-	if (!recurse && has_locked_children(old, old_path.dentry))
+	if (!recurse && has_locked_children(old, old_path.dentry) &&
+	    !capable(CAP_SYS_ADMIN))
 		goto out2;
 
 	if (recurse)
@@ -1895,7 +1901,7 @@ static int do_move_mount(struct path *path, const char *old_name)
 	if (!check_mnt(p) || !check_mnt(old))
 		goto out1;
 
-	if (old->mnt.mnt_flags & MNT_LOCKED)
+	if (!may_mount_lock(old))
 		goto out1;
 
 	err = -EINVAL;
@@ -2679,7 +2685,7 @@ SYSCALL_DEFINE2(pivot_root, const char __user *, new_root,
 		goto out4;
 	if (!check_mnt(root_mnt) || !check_mnt(new_mnt))
 		goto out4;
-	if (new_mnt->mnt.mnt_flags & MNT_LOCKED)
+	if (!may_mount_lock(new_mnt))
 		goto out4;
 	error = -ENOENT;
 	if (d_unlinked(new.dentry))
-- 
1.8.3.1