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From: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Date: Tue, 23 Aug 2016 19:38:28 +0300
Message-ID: <CAPAsAGzNcGpf+TPcqymGNdB7POoz3Oj=VLwvvtz6yWJf1UX0=g@mail.gmail.com>
Subject: Re: net: Zeroing the structure ethtool_wolinfo in ethtool_get_wol()
To: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Joe Perches <joe@perches.com>,
        Luis Henriques <luis.henriques@canonical.com>,
        Avijit Kanti Das <avijitnsec@codeaurora.org>,
        "David S . Miller" <davem@davemloft.net>,
        Ben Hutchings <ben@decadent.org.uk>,
        "netdev@vger.kernel.org" <netdev@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>
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2016-08-23 18:36 GMT+03:00 Eric Dumazet <eric.dumazet@gmail.com>:
> On Tue, 2016-08-23 at 08:05 -0700, Joe Perches wrote:
>
>> A compiler does not have a standards based requirement to
>> initialize arbitrary padding bytes.
>>
>> I believe gcc always does zero all padding anyway.
>
> I would not worry for kernel code, because the amount of scrutiny there
> will be enough to 'fix potential bugs' [1], but a lot of user land code
> would suffer from various bugs as well that might sit there forever.
>
> [1] Also, most call sites in the kernel are using same call stack, so
> the offset of '1-7 leaked bytes' vs kernel stack is constant, making
> exploits quite challenging.
>
> Even if the current standards are lazy (are they, I did not check ?),
> security needs would call for a sane compiler behavior and changing the
> standards accordingly.
>

 C11 guarantees zeroed padding.