netdev - Re: [PATCH] 6lowpan: iphc: reset mac_header after decompress to fix panic

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Date:   Tue, 3 Jul 2018 09:48:57 -0400
From:   Alexander Aring <aring@...atatu.com>
To:     Michael Scott <michael@...nsourcefoundries.com>
Cc:     Alexander Aring <alex.aring@...il.com>,
        Jukka Rissanen <jukka.rissanen@...ux.intel.com>,
        "David S. Miller" <davem@...emloft.net>,
        linux-bluetooth@...r.kernel.org, linux-wpan@...r.kernel.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] 6lowpan: iphc: reset mac_header after decompress to fix
 panic

On Tue, Jun 19, 2018 at 04:44:06PM -0700, Michael Scott wrote:
> 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@...nsourcefoundries.com>

Acked-by: Alexander Aring <aring@...atatu.com>

Thanks!

- Alex