linux-kernel - [PATCH] fs/jfs: Add check for negative db

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Message-ID: <VI1P193MB07523CD35EEB81FEEEEC168299C5A@VI1P193MB0752.EURP193.PROD.OUTLOOK.COM>
Date:   Mon,  2 Oct 2023 17:45:33 +0800
From:   Juntong Deng <juntong.deng@...look.com>
To:     shaggy@...nel.org, wonguk.lee1023@...il.com, liushixin2@...wei.com,
        andrew.kanner@...il.com, wuhoipok@...il.com
Cc:     jfs-discussion@...ts.sourceforge.net, linux-kernel@...r.kernel.org,
        linux-kernel-mentees@...ts.linuxfoundation.org,
        syzbot+debee9ab7ae2b34b0307@...kaller.appspotmail.com
Subject: [PATCH] fs/jfs: Add check for negative db_l2nbperpage

l2nbperpage is log2(number of blks per page), and the minimum legal
value should be 0, not negative.

In the case of l2nbperpage being negative, an error will occur
when subsequently used as shift exponent.

Syzbot reported this bug:

UBSAN: shift-out-of-bounds in fs/jfs/jfs_dmap.c:799:12
shift exponent -16777216 is negative

Signed-off-by: Juntong Deng <juntong.deng@...look.com>
Reported-by: syzbot+debee9ab7ae2b34b0307@...kaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=debee9ab7ae2b34b0307
---
 fs/jfs/jfs_dmap.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/jfs/jfs_dmap.c b/fs/jfs/jfs_dmap.c
index 88afd108c2dd..3a1842348112 100644
--- a/fs/jfs/jfs_dmap.c
+++ b/fs/jfs/jfs_dmap.c
@@ -180,7 +180,8 @@ int dbMount(struct inode *ipbmap)
 	bmp->db_nfree = le64_to_cpu(dbmp_le->dn_nfree);
 
 	bmp->db_l2nbperpage = le32_to_cpu(dbmp_le->dn_l2nbperpage);
-	if (bmp->db_l2nbperpage > L2PSIZE - L2MINBLOCKSIZE) {
+	if (bmp->db_l2nbperpage > L2PSIZE - L2MINBLOCKSIZE ||
+		bmp->db_l2nbperpage < 0) {
 		err = -EINVAL;
 		goto err_release_metapage;
 	}
-- 
2.39.2