jfs: add a check to prevent array-index-out-of-bounds in dbAdjTree

When the value of lp is 0 at the beginning of the for loop, it will
become negative in the next assignment and we should bail out.

Reported-by: [email protected]
Closes: https://syzkaller.appspot.com/bug?extid=412dea214d8baa3f7483
Tested-by: [email protected]
Signed-off-by: Nihar Chaithanya <[email protected]>
Signed-off-by: Dave Kleikamp <[email protected]>

Author: niharcy

fs/jfs/jfs_dmap.c

@@ -2891,6 +2891,9 @@ static void dbAdjTree(dmtree_t *tp, int leafno, int newval, bool is_ctl)
 	/* bubble the new value up the tree as required.
 	 */
 	for (k = 0; k < le32_to_cpu(tp->dmt_height); k++) {
+		if (lp == 0)
+			break;
+
 		/* get the index of the first leaf of the 4 leaf
 		 * group containing the specified leaf (leafno).
 		 */