nbd: add the check to prevent overflow in __nbd_ioctl()

If user specify a large enough value of NBD blocks option, it may trigger
signed integer overflow which may lead to nbd->config->bytesize becomes a
large or small value, zero in particular.

UBSAN: Undefined behaviour in drivers/block/nbd.c:325:31
signed integer overflow:
1024 * 4611686155866341414 cannot be represented in type 'long long int'
[...]
Call trace:
[...]
 handle_overflow+0x188/0x1dc lib/ubsan.c:192
 __ubsan_handle_mul_overflow+0x34/0x44 lib/ubsan.c:213
 nbd_size_set drivers/block/nbd.c:325 [inline]
 __nbd_ioctl drivers/block/nbd.c:1342 [inline]
 nbd_ioctl+0x998/0xa10 drivers/block/nbd.c:1395
 __blkdev_driver_ioctl block/ioctl.c:311 [inline]
[...]

Although it is not a big deal, still silence the UBSAN by limit
the input value.

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Baokun Li <libaokun1@huawei.com>

drivers/block/nbd.c

@@ -1384,6 +1384,7 @@ static int __nbd_ioctl(struct block_device *bdev, struct nbd_device *nbd,
 		       unsigned int cmd, unsigned long arg)
 {
 	struct nbd_config *config = nbd->config;
+	loff_t bytesize;
 
 	switch (cmd) {
 	case NBD_DISCONNECT:
@@ -1398,8 +1399,10 @@ static int __nbd_ioctl(struct block_device *bdev, struct nbd_device *nbd,
 	case NBD_SET_SIZE:
 		return nbd_set_size(nbd, arg, config->blksize);
 	case NBD_SET_SIZE_BLOCKS:
-		return nbd_set_size(nbd, arg * config->blksize,
-				    config->blksize);
+		if (unlikely(check_mul_overflow(arg, config->blksize,
+						&bytesize)))
+			return -EINVAL;
+		return nbd_set_size(nbd, bytesize, config->blksize);
 	case NBD_SET_TIMEOUT:
 		nbd_set_cmd_timeout(nbd, arg);
 		return 0;