Re: [PATCH 1/7] block/vdi.c: Avoid potential overflow when calculating size of write

[Kevin Wolf]

Am 31.07.2024 um 16:36 hat Peter Maydell geschrieben:
> In vdi_co_pwritev() we multiply a sector count by SECTOR_SIZE to
> get the size to write in bytes. Coverity notes that this means that
> we do the multiply as a 32x32->32 multiply before converting to
> 64 bits, which has the potential to overflow.
> 
> This is very unlikely to happen, since the block map has 4 bytes per
> block and the maximum number of blocks in the image must fit into a
> 32-bit integer.  But we can keep Coverity happy by including a cast
> so we do a 64-bit multiply here.
> 
> Resolves: Coverity CID 1508076
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
> ---
>  block/vdi.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/block/vdi.c b/block/vdi.c
> index 6363da08cee..27c60ba18d0 100644
> --- a/block/vdi.c
> +++ b/block/vdi.c
> @@ -728,7 +728,7 @@ nonallocating_write:
>          logout("will write %u block map sectors starting from entry %u\n",
>                 n_sectors, bmap_first);
>          ret = bdrv_co_pwrite(bs->file, bmap_offset * SECTOR_SIZE,
> -                             n_sectors * SECTOR_SIZE, base, 0);
> +                             n_sectors * (uint64_t)SECTOR_SIZE, base, 0);
>      }

I wonder if we shouldn't just make VDI's SECTOR_SIZE 64 bits like
BDRV_SECTOR_SIZE. It's easy to miss the cast in individual places.

Kevin