[PATCH] fs/jfs: Add checking for out-of-bounds index in binary search in xtSearch

[Juntong Deng]

There is currently no out-of-bounds check for the index in a binary
search, which may cause errors.

The following is related bug reported by Syzbot:

UBSAN: array-index-out-of-bounds in fs/jfs/jfs_xtree.c:360:4
index 18 is out of range for type 'xad_t [18]'

Checking if the index exceeds the size of the xad array can solve
this bug.

Reported-by: syzbot+76a072c2f8a60280bd70@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://syzkaller.appspot.com/bug?extid=76a072c2f8a60280bd70
Signed-off-by: Juntong Deng <juntong.deng@xxxxxxxxxxx>
---
 fs/jfs/jfs_xtree.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/jfs/jfs_xtree.c b/fs/jfs/jfs_xtree.c
index 2d304cee884c..6b55bb1e4089 100644
--- a/fs/jfs/jfs_xtree.c
+++ b/fs/jfs/jfs_xtree.c
@@ -356,6 +356,8 @@ static int xtSearch(struct inode *ip, s64 xoff,	s64 *nextp,
 		 */
 		for (base = XTENTRYSTART; lim; lim >>= 1) {
 			index = base + (lim >> 1);
+			if (index >= XTROOTMAXSLOT)
+				break;
 
 			XT_CMP(cmp, xoff, &p->xad[index], t64);
 			if (cmp == 0) {
-- 
2.39.2