[PATCH] Do without union of variable length arrays.

Alexander Cherepanov ch3root at openwall.com
Thu Oct 1 20:45:24 UTC 2015


On 2015-09-17 12:40, Mark Wielaard wrote:
>> * Now const size_t is used instead of const int for malloc argument type.
>
> Thanks. I am still interested in the overflow issue. I believe since we
> are using unsigned arithmetic and we know the size is always > 0, it
> should be as simple as doing:
>
>    const size_t elem_size = ... sizeof (...);
>    const size_t bytes = num * elem_size;
>    if (unlikely (bytes / elem_size != num))
>      return E_NOMEM;
>    ... malloc (bytes);

Sorry, I'm late to the party but why hot check it before multiplication 
in a usual way:

if (num > SIZE_MAX / elem_size)
   return E_NOMEM;

IIUC elem_size is a compile time constant so the whole division is 
computed by compiler.

-- 
Alexander Cherepanov


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