Re: [PATCH] infiniband: avoid overflow warning

[Kees Cook]

On Mon, Jul 31, 2017 at 2:10 PM, Arnd Bergmann <arnd@xxxxxxxx> wrote:
> On Mon, Jul 31, 2017 at 10:58 PM, Kees Cook <keescook@xxxxxxxxxxxx> wrote:
>> On Mon, Jul 31, 2017 at 12:30 AM, Arnd Bergmann <arnd@xxxxxxxx> wrote:
>>> On Mon, Jul 31, 2017 at 9:08 AM, Moni Shoua <monis@xxxxxxxxxxxx> wrote:
>>>>>                 break;
>>>>>         default:
>>>>>                 return -EINVAL;
>>>> what happens if you replace 16 with sizeof(struct in6_addr)?
>>>
>>> Same thing: the problem is that gcc already knows the size of the structure we
>>> pass in here, and it is in fact shorter.
>>
>> So gcc is ignoring both the cast (to 16 byte struct in6_addr) and the
>> caller's actual 128 byte struct sockaddr_storage, and looking only at
>> struct sockaddr? That seems really weird.
>
> Using a sockaddr_storage on the stack would address the warning, but
> the question was about just changing the hardcoded 16 to a sizeof()
> operation, and that has no effect.

Right, I didn't mean that; I was curious why the fortify macro
resulted in an error at all. The callers are casting from struct
sockaddr_storage (large enough) to struct sockaddr (not large enough),
and then the inline is casting back to sockaddr_in6 (large enough). I
would have expected fortify to check either sockaddr_storage or
sockaddr_in6, but not sockaddr.

-Kees

-- 
Kees Cook
Pixel Security