Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Subject: Re: [PATCH AUTOSEL 4.19 15/68] batman-adv: Expand merged fragment
 buffer for full packet
To:     Sasha Levin <sashal@kernel.org>, stable@vger.kernel.org,
        linux-kernel@vger.kernel.org
Cc:     Sven Eckelmann <sven@narfation.org>,
        Simon Wunderlich <sw@simonwunderlich.de>,
        netdev@vger.kernel.org
References: <20181129055559.159228-1-sashal@kernel.org>
 <20181129055559.159228-15-sashal@kernel.org>
From:   Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Organization: Cogent Embedded
Message-ID: <cad9ec40-5125-9bef-0e9e-5c70783a5cb7@cogentembedded.com>
Date:   Thu, 29 Nov 2018 13:00:22 +0300
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101
 Thunderbird/52.2.1
MIME-Version: 1.0
In-Reply-To: <20181129055559.159228-15-sashal@kernel.org>
Content-Type: text/plain; charset=utf-8
Content-Language: en-MW
Content-Transfer-Encoding: 8bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Hello!

On 11/29/2018 08:55 AM, Sasha Levin wrote:

> From: Sven Eckelmann <sven@narfation.org>
> 
> [ Upstream commit d7d8bbb40a5b1f682ee6589e212934f4c6b8ad60 ]
> 
> The complete size ("total_size") of the fragmented packet is stored in the
> fragment header and in the size of the fragment chain. When the fragments
> are ready for merge, the skbuff's tail of the first fragment is expanded to
> have enough room after the data pointer for at least total_size. This means
> that it gets expanded by total_size - first_skb->len.
> 
> But this is ignoring the fact that after expanding the buffer, the fragment
> header is pulled by from this buffer. Assuming that the tailroom of the

   Pulled by what?

> buffer was already 0, the buffer after the data pointer of the skbuff is
> now only total_size - len(fragment_header) large. When the merge function
> is then processing the remaining fragments, the code to copy the data over
> to the merged skbuff will cause an skb_over_panic when it tries to actually
> put enough data to fill the total_size bytes of the packet.
> 
> The size of the skb_pull must therefore also be taken into account when the
> buffer's tailroom is expanded.
> 
> Fixes: 610bfc6bc99b ("batman-adv: Receive fragmented packets and merge")
> Reported-by: Martin Weinelt <martin@darmstadt.freifunk.net>
> Co-authored-by: Linus Lüssing <linus.luessing@c0d3.blue>
> Signed-off-by: Sven Eckelmann <sven@narfation.org>
> Signed-off-by: Simon Wunderlich <sw@simonwunderlich.de>
> Signed-off-by: Sasha Levin <sashal@kernel.org>
[...]

MBR, Sergei