Re: [Qemu-devel] [Qemu-block] [PATCH 1/2] block: Detect multiplication overflow in bdrv_getlength

[Alberto Garcia]

On Fri 15 May 2015 03:39:10 AM CEST, Fam Zheng <address@hidden> wrote:

>      int64_t ret = bdrv_nb_sectors(bs);
>  
> +    ret = (int64_t)(ret * BDRV_SECTOR_SIZE) < 0 ? -EFBIG : ret;
>      return ret < 0 ? ret : ret * BDRV_SECTOR_SIZE;

Maybe in this case you're safe, but in general there's no guarantee that
if there's an overflow the result will be negative.

You can do something like this instead:

   ret = ret > INT64_MAX / BDRV_SECTOR_SIZE ? -EFBIG : ret;

Of course this is only valid if BDRV_SECTOR_SIZE != 0 ;)

Berto