[PATCH] jfs: add a check to prevent array-index-out-of-bounds

[Nihar Chaithanya]

When the value of lp is 1 at the end of the iteration in the for loop,
lp is modified in the next iteration to a negative value.
Add a check to prevent this condition.

Reported-by: syzbot+412dea214d8baa3f7483@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://syzkaller.appspot.com/bug?extid=412dea214d8baa3f7483
Tested-by: syzbot+412dea214d8baa3f7483@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Nihar Chaithanya <niharchaithanya@xxxxxxxxx>
---
 fs/jfs/jfs_dmap.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/fs/jfs/jfs_dmap.c b/fs/jfs/jfs_dmap.c
index 5713994328cb..3ebb2dfdd0b3 100644
--- a/fs/jfs/jfs_dmap.c
+++ b/fs/jfs/jfs_dmap.c
@@ -2911,6 +2911,12 @@ static void dbAdjTree(dmtree_t *tp, int leafno, int newval, bool is_ctl)
 		 */
 		tp->dmt_stree[pp] = max;
 
+		/* check to prevent negative value of lp on the
+		 * next iteration.
+		 */
+		if (lp == 1)
+			break;
+
 		/* parent becomes leaf for next go-round.
 		 */
 		lp = pp;
-- 
2.34.1