linux-kernel - [PATCH] jfs: jfs_dmap: Validate db

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Date:   Mon,  5 Jun 2023 19:31:51 +0530
From:   Siddh Raman Pant <code@...dh.me>
To:     Dave Kleikamp <shaggy@...nel.org>,
        Dongliang Mu <mudongliangabcd@...il.com>,
        Liu Shixin <liushixin2@...wei.com>,
        Hoi Pok Wu <wuhoipok@...il.com>
Cc:     jfs-discussion@...ts.sourceforge.net, linux-kernel@...r.kernel.org,
        Anup Sharma <anupnewsmail@...il.com>,
        syzbot+d2cd27dcf8e04b232eb2@...kaller.appspotmail.com,
        stable@...r.kernel.org
Subject: [PATCH] jfs: jfs_dmap: Validate db_l2nbperpage while mounting

In jfs_dmap.c at line 381, BLKTODMAP is used to get a logical block
number inside dbFree(). db_l2nbperpage, which is the log2 number of
blocks per page, is passed as an argument to BLKTODMAP which uses it
for shifting.

Syzbot reported a shift out-of-bounds crash because db_l2nbperpage is
too big. This happens because the large value is set without any
validation in dbMount() at line 181.

Thus, make sure that db_l2nbperpage is correct while mounting.

Reported-and-tested-by: syzbot+d2cd27dcf8e04b232eb2@...kaller.appspotmail.com
Link: https://syzkaller.appspot.com/bug?id=2a70a453331db32ed491f5cbb07e81bf2d225715
Cc: stable@...r.kernel.org
Signed-off-by: Siddh Raman Pant <code@...dh.me>
---
 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 a3eb1e826947..62f058822a3a 100644
--- a/fs/jfs/jfs_dmap.c
+++ b/fs/jfs/jfs_dmap.c
@@ -178,7 +178,13 @@ int dbMount(struct inode *ipbmap)
 	dbmp_le = (struct dbmap_disk *) mp->data;
 	bmp->db_mapsize = le64_to_cpu(dbmp_le->dn_mapsize);
 	bmp->db_nfree = le64_to_cpu(dbmp_le->dn_nfree);
+
 	bmp->db_l2nbperpage = le32_to_cpu(dbmp_le->dn_l2nbperpage);
+	if (bmp->db_l2nbperpage > L2MAXL0SIZE) {
+		err = -EINVAL;
+		goto err_release_metapage;
+	}
+
 	bmp->db_numag = le32_to_cpu(dbmp_le->dn_numag);
 	if (!bmp->db_numag) {
 		err = -EINVAL;
-- 
2.39.2