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

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Message-ID: <CAG_fn=VAnDL1UpNe+VQMhSdwgU-cN_PybRLx5-cgW+QdNTmryw@mail.gmail.com>
Date:   Tue, 25 Apr 2017 18:38:39 +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 6:32 PM, David Miller <davem@...emloft.net> wrote:
> From: Alexander Potapenko <glider@...gle.com>
> Date: Tue, 25 Apr 2017 18:27:04 +0200
>
>> 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?)
>
> They are currently getting corrupt data depending upon the endianness,
> so -EINVAL is a serious improvement.
On a second glance getsockopt() already returns -EINVAL in some cases,
so man is already imprecise.


-- 
Alexander Potapenko
Software Engineer

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