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Subject: Re: [PATCH] 6lowpan: iphc: reset mac_header after decompress to fix
 panic
From:   Marcel Holtmann <marcel@holtmann.org>
In-Reply-To: <20180619234406.8217-1-michael@opensourcefoundries.com>
Date:   Fri, 6 Jul 2018 12:46:20 +0200
Cc:     Alexander Aring <alex.aring@gmail.com>,
        Jukka Rissanen <jukka.rissanen@linux.intel.com>,
        "David S. Miller" <davem@davemloft.net>,
        linux-bluetooth@vger.kernel.org, linux-wpan@vger.kernel.org,
        netdev@vger.kernel.org, linux-kernel@vger.kernel.org
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Message-Id: <3AAE601A-9D04-4BC5-8D96-5570F4C53F3B@holtmann.org>
References: <20180619234406.8217-1-michael@opensourcefoundries.com>
To:     Michael Scott <michael@opensourcefoundries.com>
Sender: linux-kernel-owner@vger.kernel.org
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Hi Michael,

> After decompression of 6lowpan socket data, an IPv6 header is inserted
> before the existing socket payload.  After this, we reset the
> network_header value of the skb to account for the difference in payload
> size from prior to decompression + the addition of the IPv6 header.
> 
> However, we fail to reset the mac_header value.
> 
> Leaving the mac_header value untouched here, can cause a calculation
> error in net/packet/af_packet.c packet_rcv() function when an
> AF_PACKET socket is opened in SOCK_RAW mode for use on a 6lowpan
> interface.
> 
> On line 2088, the data pointer is moved backward by the value returned
> from skb_mac_header().  If skb->data is adjusted so that it is before
> the skb->head pointer (which can happen when an old value of mac_header
> is left in place) the kernel generates a panic in net/core/skbuff.c
> line 1717.
> 
> This panic can be generated by BLE 6lowpan interfaces (such as bt0) and
> 802.15.4 interfaces (such as lowpan0) as they both use the same 6lowpan
> sources for compression and decompression.
> 
> Signed-off-by: Michael Scott <michael@opensourcefoundries.com>
> ---
> net/6lowpan/iphc.c | 1 +
> 1 file changed, 1 insertion(+)

patch has been applied to bluetooth-next tree.

Regards

Marcel