VFS: move BUG_ON test for symlink nd->depth after current->link_count test

This solves a serious VFS-level bug in nested_symlink (which was
rewritten from do_follow_link), and follows the order of depth tests
that existed before.

The bug triggers a BUG_ON in fs/namei.c:1381, when running racer with
symlink and rename ops.

Signed-off-by: Erez Zadok <ezk@cs.sunysb.edu>
Acked-by: Miklos Szeredi <mszeredi@suse.cz>
Cc: stable@kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/fs/namei.c b/fs/namei.c
index e3c4f11..6ff858c 100644 (file)
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1378,12 +1378,12 @@ static inline int nested_symlink(struct path *path, struct nameidata *nd)
 {
        int res;
 
-       BUG_ON(nd->depth >= MAX_NESTED_LINKS);
        if (unlikely(current->link_count >= MAX_NESTED_LINKS)) {
                path_put_conditional(path, nd);
                path_put(&nd->path);
                return -ELOOP;
        }
+       BUG_ON(nd->depth >= MAX_NESTED_LINKS);
 
        nd->depth++;
        current->link_count++;