mnt: Fix the error check in __detach_mounts

commit f53e57975151f54ad8caa1b0ac8a78091cd5700a upstream.

lookup_mountpoint can return either NULL or an error value.
Update the test in __detach_mounts to test for an error value
to avoid pathological cases causing a NULL pointer dereferences.

The callers of __detach_mounts should prevent it from ever being
called on an unlinked dentry but don't take any chances.

Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/namespace.c b/fs/namespace.c
index 24de1e9b1d49847a7112acfc2059725365b51d0d..9e338951c4d03b16665d405c8cb58457a663ddc9 100644 (file)
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1518,7 +1518,7 @@ void __detach_mounts(struct dentry *dentry)
 
        namespace_lock();
        mp = lookup_mountpoint(dentry);
-       if (!mp)
+       if (IS_ERR_OR_NULL(mp))
                goto out_unlock;
 
        lock_mount_hash();