linux-kernel - [PATCH 1/1] squashfs: harden sanity check in squashfs_read_xattr_id

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Message-Id: <20230117105226.329303-2-pchelkin@ispras.ru>
Date:   Tue, 17 Jan 2023 13:52:26 +0300
From:   Fedor Pchelkin <pchelkin@...ras.ru>
To:     Phillip Lougher <phillip@...ashfs.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     Fedor Pchelkin <pchelkin@...ras.ru>, linux-kernel@...r.kernel.org,
        Alexey Khoroshilov <khoroshilov@...ras.ru>,
        lvc-project@...uxtesting.org,
        syzbot+082fa4af80a5bb1a9843@...kaller.appspotmail.com
Subject: [PATCH 1/1] squashfs: harden sanity check in squashfs_read_xattr_id_table

While mounting a corrupted filesystem, a signed integer '*xattr_ids' can
become less than zero. This leads to the incorrect computation of 'len'
and 'indexes' values which can cause null-ptr-deref in copy_bio_to_actor()
or out-of-bounds accesses in the next sanity checks inside
squashfs_read_xattr_id_table().

Found by Linux Verification Center (linuxtesting.org) with Syzkaller.

Fixes: 506220d2ba21 ("squashfs: add more sanity checks in xattr id lookup")
Reported-by: syzbot+082fa4af80a5bb1a9843@...kaller.appspotmail.com
Signed-off-by: Fedor Pchelkin <pchelkin@...ras.ru>
Signed-off-by: Alexey Khoroshilov <khoroshilov@...ras.ru>
---
 fs/squashfs/xattr_id.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/squashfs/xattr_id.c b/fs/squashfs/xattr_id.c
index 087cab8c78f4..f6d78cbc3e74 100644
--- a/fs/squashfs/xattr_id.c
+++ b/fs/squashfs/xattr_id.c
@@ -76,7 +76,7 @@ __le64 *squashfs_read_xattr_id_table(struct super_block *sb, u64 table_start,
 	/* Sanity check values */
 
 	/* there is always at least one xattr id */
-	if (*xattr_ids == 0)
+	if (*xattr_ids <= 0)
 		return ERR_PTR(-EINVAL);
 
 	len = SQUASHFS_XATTR_BLOCK_BYTES(*xattr_ids);
-- 
2.34.1