netdev - Re: [PATCH v2] net/packet: initialize val in packet

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Message-ID: <CAG_fn=URNuXxc7wEaXd_p7B46RRCYYMTv5rOVc_U1CdvervzPQ@mail.gmail.com>
Date:   Tue, 25 Apr 2017 18:27:04 +0200
From:   Alexander Potapenko <glider@...gle.com>
To:     David Miller <davem@...emloft.net>
Cc:     Dmitriy Vyukov <dvyukov@...gle.com>,
        Kostya Serebryany <kcc@...gle.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        LKML <linux-kernel@...r.kernel.org>,
        Networking <netdev@...r.kernel.org>
Subject: Re: [PATCH v2] net/packet: initialize val in packet_getsockopt()

On Tue, Apr 25, 2017 at 5:44 PM, David Miller <davem@...emloft.net> wrote:
> From: Alexander Potapenko <glider@...gle.com>
> Date: Mon, 24 Apr 2017 14:59:14 +0200
>
>> In the case getsockopt() is called with PACKET_HDRLEN and optlen < 4
>> |val| remains uninitialized and the syscall may behave differently
>> depending on its value. This doesn't have security consequences (as the
>> uninit bytes aren't copied back), but it's still cleaner to initialize
>> |val| and ensure optlen is not less than sizeof(int).
>>
>> This bug has been detected with KMSAN.
>>
>> Signed-off-by: Alexander Potapenko <glider@...gle.com>
>> ---
>> v2: - if len < sizeof(int), make it 0
>
> No, you should signal an error if the len is too small.
According to manpages, only setsockopt() may return EINVAL.
Is it ok to change the behavior of getsockopt() to return EINVAL in
this case? (I.e. won't we break existing users that don't expect it?)
> Returning zero bytes to userspace silently makes the user think that
> he got the data he asked for.



-- 
Alexander Potapenko
Software Engineer

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