Hi, 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@xxxxxxxxxxxxxxxxxxxxxxx> > --- > net/6lowpan/iphc.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/net/6lowpan/iphc.c b/net/6lowpan/iphc.c > index 6b1042e21656..52fad5dad9f7 100644 > --- a/net/6lowpan/iphc.c > +++ b/net/6lowpan/iphc.c > @@ -770,6 +770,7 @@ int lowpan_header_decompress(struct sk_buff *skb, const struct net_device *dev, > hdr.hop_limit, &hdr.daddr); > > skb_push(skb, sizeof(hdr)); > + skb_reset_mac_header(skb); > skb_reset_network_header(skb); > skb_copy_to_linear_data(skb, &hdr, sizeof(hdr)); > I think it's good to make that if the mac_header gets a dangled pointer. But we don't have a mac header at this point anymore... There exists also some functionality that the MAC header is not set, I suppose this can be usefuly for tun like interfaces e.g. RAW IP what we have here. skb_mac_header_was_set which does: return skb->mac_header != (typeof(skb->mac_header))~0U; maybe we can set it as (typeof(skb->mac_header))~0U and then everything will run as far the kernel will not crash anymore. Question is for me: which upper layer wants access MAC header here on receive path? It cannot parsed anyhow because so far I know no upper layer can parse at the moment 802.15.4 frames (which is a complex format). Maybe over some header_ops callback? - Alex -- To unsubscribe from this list: send the line "unsubscribe linux-wpan" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
