linux-kernel - Re: [PATCH] infiniband: avoid overflow warning

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Date:   Mon, 31 Jul 2017 09:30:12 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Moni Shoua <monis@...lanox.com>
Cc:     Doug Ledford <dledford@...hat.com>,
        Sean Hefty <sean.hefty@...el.com>,
        Hal Rosenstock <hal.rosenstock@...il.com>,
        Daniel Micay <danielmicay@...il.com>,
        Kees Cook <keescook@...omium.org>,
        "Kalderon, Michal" <Michal.Kalderon@...ium.com>,
        Ariel Elior <Ariel.Elior@...ium.com>,
        "David S. Miller" <davem@...emloft.net>,
        Bart Van Assche <bart.vanassche@...disk.com>,
        Parav Pandit <parav@...lanox.com>,
        Noa Osherovich <noaos@...lanox.com>,
        linux-rdma <linux-rdma@...r.kernel.org>,
        Linux Kernel Mailinglist <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] infiniband: avoid overflow warning

On Mon, Jul 31, 2017 at 9:08 AM, Moni Shoua <monis@...lanox.com> wrote:
> On Mon, Jul 31, 2017 at 9:50 AM, Arnd Bergmann <arnd@...db.de> wrote:
>> --- a/include/rdma/ib_addr.h
>> +++ b/include/rdma/ib_addr.h
>> @@ -172,7 +172,8 @@ static inline int rdma_ip2gid(struct sockaddr *addr, union ib_gid *gid)
>>                                        (struct in6_addr *)gid);
>>                 break;
>>         case AF_INET6:
>> -               memcpy(gid->raw, &((struct sockaddr_in6 *)addr)->sin6_addr, 16);
>> +               *(struct in6_addr *)&gid->raw =
>> +                       ((struct sockaddr_in6 *)addr)->sin6_addr;
>>                 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.

I also tried changing the struct sockaddr pointer to a sockaddr_storage pointer,
without success. Other approaches that do work are:

- mark addr_event() as "noinline" to prevent gcc from seeing the true
size of the
  inetaddr_event stack object in rdma_ip2gid(). I considered this a little ugly.

- change inetaddr_event to put a larger structure on the stack, using
  sockaddr_storage or sockaddr_in6. This would be less efficient.

- define a union of sockaddr_in and sockaddr_in6, and use that as the argument
  to rdma_ip2gid/rdma_gid2ip, and change all callers to use that union type.
  This is probably the cleanest approach as it gets rid of a lot of questionable
  type casts, but it's a relatively large patch and also slightly less
efficient as we have
  to zero more stack storage in some cases.

        Arnd