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

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Message-Id: <20170425.123201.1910437101082999848.davem@davemloft.net>
Date:   Tue, 25 Apr 2017 12:32:01 -0400 (EDT)
From:   David Miller <davem@...emloft.net>
To:     glider@...gle.com
Cc:     dvyukov@...gle.com, kcc@...gle.com, edumazet@...gle.com,
        kuznet@....inr.ac.ru, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org
Subject: Re: [PATCH v2] net/packet: initialize val in packet_getsockopt()

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.