debugfs: fix refcount imbalance in start_creating

In debugfs' start_creating(), we pin the file system to safely access
its root. When we failed to create a file, we unpin the file system via
failed_creating() to release the mount count and eventually the reference
of the vfsmount.

However, when we run into an error during lookup_one_len() when still
in start_creating(), we only release the parent's mutex but not so the
reference on the mount. Looks like it was done in the past, but after
splitting portions of __create_file() into start_creating() and
end_creating() via 190afd81e4a5 ("debugfs: split the beginning and the
end of __create_file() off"), this seemed missed. Noticed during code
review.

Fixes: 190afd81e4a5 ("debugfs: split the beginning and the end of __create_file() off")
Cc: stable@vger.kernel.org # v4.0+
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

diff --git a/fs/debugfs/inode.c b/fs/debugfs/inode.c
index 5d8f35f1382ab11032f50dcd7029c40f5adf2159..b7fcc0de0b2f2771aff08a130eb20564adb3cbd4 100644 (file)
--- a/fs/debugfs/inode.c
+++ b/fs/debugfs/inode.c
@@ -271,8 +271,12 @@ static struct dentry *start_creating(const char *name, struct dentry *parent)
                dput(dentry);
                dentry = ERR_PTR(-EEXIST);
        }
-       if (IS_ERR(dentry))
+
+       if (IS_ERR(dentry)) {
                mutex_unlock(&d_inode(parent)->i_mutex);
+               simple_release_fs(&debugfs_mount, &debugfs_mount_count);
+       }
+
        return dentry;
 }