Re: [Qemu-block] [Qemu-devel] [PATCH for-2.9] block/parallels: Avoid overflows

[Philippe Mathieu-Daudé]

On 03/31/2017 02:05 PM, Max Reitz wrote:
> Change the types of variables in allocate_clusters() to int64_t so we do
> not have to worry about potential overflows.
>
> Add an assertion that our accesses to s->bat[] do not result in a buffer
> overflow and that the implicit conversion performed when invoking
> bat_entry_off() does not result in an integer overflow.
>
> Coverity-id: 1307776
> Signed-off-by: Max Reitz <address@hidden>

Reviewed-by: Philippe Mathieu-Daudé <address@hidden>

> ---
> This supercedes Peter's patch "block/parallels.c: avoid integer overflow
> in allocate_clusters()".
> ---
>  block/parallels.c | 19 +++++++++++++------
>  1 file changed, 13 insertions(+), 6 deletions(-)
>
> diff --git a/block/parallels.c b/block/parallels.c
> index 4173b3fb9d..90acf79687 100644
> --- a/block/parallels.c
> +++ b/block/parallels.c
> @@ -192,8 +192,7 @@ static int64_t allocate_clusters(BlockDriverState *bs, 
> int64_t sector_num,
>                                   int nb_sectors, int *pnum)
>  {
>      BDRVParallelsState *s = bs->opaque;
> -    uint32_t idx, to_allocate, i;
> -    int64_t pos, space;
> +    int64_t pos, space, idx, to_allocate, i;
>
>      pos = block_status(s, sector_num, nb_sectors, pnum);
>      if (pos > 0) {
> @@ -201,11 +200,19 @@ static int64_t allocate_clusters(BlockDriverState *bs, 
> int64_t sector_num,
>      }
>
>      idx = sector_num / s->tracks;
> -    if (idx >= s->bat_size) {
> -        return -EINVAL;
> -    }
> -
>      to_allocate = DIV_ROUND_UP(sector_num + *pnum, s->tracks) - idx;
> +
> +    /* This function is called only by parallels_co_writev(), which will never
> +     * pass a sector_num at or beyond the end of the image (because the block
> +     * layer never passes such a sector_num to that function). Therefore, idx
> +     * is always below s->bat_size.
> +     * block_status() will limit *pnum so that sector_num + *pnum will not
> +     * exceed the image end. Therefore, idx + to_allocate cannot exceed
> +     * s->bat_size.
> +     * Note that s->bat_size is an unsigned int, therefore idx + to_allocate
> +     * will always fit into a uint32_t. */
> +    assert(idx < s->bat_size && idx + to_allocate <= s->bat_size);
> +
>      space = to_allocate * s->tracks;
>      if (s->data_end + space > bdrv_getlength(bs->file->bs) >> 
> BDRV_SECTOR_BITS) {
>          int ret;