nbd: don't allow invalid blocksize settings

axboe · axboe · commit bc811f05d77f · 2018-09-04T11:54:58.000-06:00
syzbot reports a divide-by-zero off the NBD_SET_BLKSIZE ioctl.
We need proper validation of the input here. Not just if it's
zero, but also if the value is a power-of-2 and in a valid
range. Add that.

Cc: stable@vger.kernel.org
Reported-by: syzbot &lt;syzbot+25dbecbec1e62c6b0dd4@syzkaller.appspotmail.com&gt;
Reviewed-by: Josef Bacik &lt;josef@toxicpanda.com&gt;
Signed-off-by: Jens Axboe &lt;axboe@kernel.dk&gt;
diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
@@ -1239,6 +1239,9 @@ static int __nbd_ioctl(struct block_device *bdev, struct nbd_device *nbd,
 	case NBD_SET_SOCK:
 		return nbd_add_socket(nbd, arg, false);
 	case NBD_SET_BLKSIZE:
+		if (!arg || !is_power_of_2(arg) || arg < 512 ||
+		    arg > PAGE_SIZE)
+			return -EINVAL;
 		nbd_size_set(nbd, arg,
 			     div_s64(config->bytesize, arg));
 		return 0;
