From fb52b550be82812b6e9a4eeb0bc80bf1ae67de0b Mon Sep 17 00:00:00 2001
From: Daniel Axtens <dja@axtens.net>
Date: Mon, 18 Jan 2021 14:51:11 +1100
Subject: [PATCH] fs/jfs: Do not move to leaf level if name length is negative

Fuzzing JFS revealed crashes where a negative number would be passed
to le_to_cpu16_copy(). There it would be cast to a large positive number
and the copy would read and write off the end of the respective buffers.

Catch this at the top as well as the bottom of the loop.

Reference: http://git.savannah.gnu.org/cgit/grub.git/commit/?id=ffd5a46f68710e2781899d0be4d701429a5a817d

Signed-off-by: Daniel Axtens <dja@axtens.net>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
---
 grub-core/fs/jfs.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/grub-core/fs/jfs.c b/grub-core/fs/jfs.c
index d5a6d65..e5bbda6 100644
--- a/grub-core/fs/jfs.c
+++ b/grub-core/fs/jfs.c
@@ -567,7 +567,7 @@ grub_jfs_getent (struct grub_jfs_diropen *diro)
 
   /* Move down to the leaf level.  */
   nextent = leaf->next;
-  if (leaf->next != 255)
+  if (leaf->next != 255 && len > 0)
     do
       {
  	next_leaf = &diro->next_leaf[nextent];
-- 
2.19.1

