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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org,
        syzbot+6f1624f937d9d6911e2d@syzkaller.appspotmail.com,
        OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>,
        Andrew Morton <akpm@linux-foundation.org>,
        Marco Elver <elver@google.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Linus Torvalds <torvalds@linux-foundation.org>
Subject: [PATCH 4.9 049/128] fat: dont allow to mount if the FAT length == 0
Date:   Fri, 19 Jun 2020 16:32:23 +0200
Message-Id: <20200619141622.792607521@linuxfoundation.org>
In-Reply-To: <20200619141620.148019466@linuxfoundation.org>
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From: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>

commit b1b65750b8db67834482f758fc385bfa7560d228 upstream.

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>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Marco Elver <elver@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Link: http://lkml.kernel.org/r/87r1wz8mrd.fsf@mail.parknet.co.jp
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 fs/fat/inode.c |    6 ++++++
 1 file changed, 6 insertions(+)

--- a/fs/fat/inode.c
+++ b/fs/fat/inode.c
@@ -1512,6 +1512,12 @@ 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: