[PATCH 4.14 068/190] fat: dont allow to mount if the FAT length == 0

Greg Kroah-Hartman
2020-06-19T14:49:09Z

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;