From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ben McKeegan Subject: [PATCH] ppp: fix BUG on non-linear SKB (multilink receive) Date: Thu, 12 Nov 2009 13:09:57 +0000 (GMT) Message-ID: Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII To: davem@davemloft.net, paulus@samba.org, netdev@vger.kernel.org, linux-ppp@vger.kernel.org Return-path: Sender: linux-ppp-owner@vger.kernel.org List-Id: netdev.vger.kernel.org PPP does not correctly call pskb_may_pull() on all necessary receive paths before reading the PPP protocol, thus causing PPP to report seemingly random 'unsupported protocols' and eventually trigger BUG_ON(skb->len < skb->data_len) in skb_pull_rcsum() when receiving multilink protocol in non-linear skbs. ppp_receive_nonmp_frame() does not call pskb_may_pull() before reading the protocol number. For the non-mp receive path this is not a problem, as this check is done in ppp_receive_frame(). For the mp receive path, ppp_mp_reconstruct() usually copies the data into a new linear skb. However, in the case where the frame is made up of a single mp fragment, the mp header is pulled and the existing skb used. This skb was then passed to ppp_receive_nonmp_frame() without checking if the encapsulated protocol header can safely be read. Signed-off-by: Ben McKeegan --- This a long standing bug we have observed with PPP over L2TP received on an e1000e interface, although it may arise with other PPP encapsulations or devices. diff -uprN linux-2.6.31.6/drivers/net/ppp_generic.c linux-2.6.31.6-ppp-non-linear-skb/drivers/net/ppp_generic.c --- linux-2.6.31.6/drivers/net/ppp_generic.c 2009-11-10 00:32:31.000000000 +0000 +++ linux-2.6.31.6-ppp-non-linear-skb/drivers/net/ppp_generic.c 2009-11-12 11:58:40.000000000 +0000 @@ -1944,7 +1944,13 @@ ppp_receive_mp_frame(struct ppp *ppp, st /* Pull completed packets off the queue and receive them. */ while ((skb = ppp_mp_reconstruct(ppp))) - ppp_receive_nonmp_frame(ppp, skb); + if (pskb_may_pull(skb, 2)) + ppp_receive_nonmp_frame(ppp, skb); + else { + ++ppp->dev->stats.rx_length_errors; + kfree_skb(skb); + ppp_receive_error(ppp); + } return;