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From:   OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
To:     Andrew Morton <akpm@linux-foundation.org>
Cc:     syzbot <syzbot+6f1624f937d9d6911e2d@syzkaller.appspotmail.com>,
        Marco Elver <elver@google.com>,
        LKML <linux-kernel@vger.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@googlegroups.com>,
        syzkaller <syzkaller@googlegroups.com>,
        Dmitry Vyukov <dvyukov@google.com>
Subject: [PATCH] fat: Don't allow to mount if the FAT length == 0
Date:   Tue, 07 Apr 2020 22:10:30 +0900
Message-ID: <87r1wz8mrd.fsf@mail.parknet.co.jp>
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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@syzkaller.appspotmail.com
Signed-off-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
---
 fs/fat/inode.c |    6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/fs/fat/inode.c b/fs/fat/inode.c
index 71946da..bf8e04e 100644
--- a/fs/fat/inode.c	2020-04-07 21:55:27.001147223 +0900
+++ b/fs/fat/inode.c	2020-04-07 22:06:15.164098069 +0900
@@ -1520,6 +1520,12 @@ static int fat_read_bpb(struct super_blo
 		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:
_
OGAWA Hirofumi <hirofumi@mail.parknet.co.jp> writes: