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

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Message-Id: <20170420.155620.2005862240803164222.davem@davemloft.net>
Date:   Thu, 20 Apr 2017 15:56:20 -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] net/packet: initialize val in packet_getsockopt()

From: Alexander Potapenko <glider@...gle.com>
Date: Tue, 18 Apr 2017 19:47:08 +0200

> In the case getsockopt() is called with PACKET_HDRLEN and zero length,
> |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|.
> 
> This bug has been detected with KMSAN.
> 
> Signed-off-by: Alexander Potapenko <glider@...gle.com>

Copying into an 'int' only 1, 2, or 3 bytes is not going to work
properly.

Either enforce that it must be 4 bytes long, or handle the smaller
sizes properly such that it will work regardless of endianness.

Thanks.