From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ben McKeegan Subject: Re: [PATCH] ppp: fix BUG on non-linear SKB (multilink receive) Date: Mon, 16 Nov 2009 13:44:25 +0000 (GMT) Message-ID: References: <20091113.194650.214404898.davem@davemloft.net> Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Cc: paulus@samba.org, netdev@vger.kernel.org, linux-ppp@vger.kernel.org To: David Miller Return-path: In-Reply-To: <20091113.194650.214404898.davem@davemloft.net> 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 could safely be read. Signed-off-by: Ben McKeegan --- 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 2009-11-16 13:14:22.000000000 +0000 @@ -1943,8 +1943,15 @@ 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); + while ((skb = ppp_mp_reconstruct(ppp))) { + 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;