linux-kernel - [PATCH AUTOSEL 4.4 18/60] fat: don't allow to mount if the FAT length == 0

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Date:   Wed, 17 Jun 2020 21:29:22 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>,
        syzbot+6f1624f937d9d6911e2d@...kaller.appspotmail.com,
        Andrew Morton <akpm@...ux-foundation.org>,
        Marco Elver <elver@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH AUTOSEL 4.4 18/60] fat: don't allow to mount if the FAT length == 0

From: OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>

[ Upstream commit b1b65750b8db67834482f758fc385bfa7560d228 ]

If FAT length == 0, the image doesn't have any data. And it can be the
cause of overlapping the root dir and FAT entries.

Also Windows treats it as invalid format.

Reported-by: syzbot+6f1624f937d9d6911e2d@...kaller.appspotmail.com
Signed-off-by: OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Cc: Marco Elver <elver@...gle.com>
Cc: Dmitry Vyukov <dvyukov@...gle.com>
Link: http://lkml.kernel.org/r/87r1wz8mrd.fsf@mail.parknet.co.jp
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 fs/fat/inode.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/fs/fat/inode.c b/fs/fat/inode.c
index 5e87b9aa7ba6..944fff1ef536 100644
--- a/fs/fat/inode.c
+++ b/fs/fat/inode.c
@@ -1422,6 +1422,12 @@ static int fat_read_bpb(struct super_block *sb, struct fat_boot_sector *b,
 		goto out;
 	}
 
+	if (bpb->fat_fat_length == 0 && bpb->fat32_length == 0) {
+		if (!silent)
+			fat_msg(sb, KERN_ERR, "bogus number of FAT sectors");
+		goto out;
+	}
+
 	error = 0;
 
 out:
-- 
2.25.1