nbd: don't allow invalid blocksize settings

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 <syzbot+25dbecbec1e62c6b0dd4@syzkaller.appspotmail.com>
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
index 3863c00..14a5125 100644 (file)
--- 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;