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

From: Marcel Holtmann
Date: Fri Jul 06 2018 - 06:46:31 EST

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@xxxxxxxxxxxxxxxxxxxxxxx>
> ---
> net/6lowpan/iphc.c | 1 +
> 1 file changed, 1 insertion(+)

patch has been applied to bluetooth-next tree.