From 82b3cc1a2f5e46300a9dec4a8cc8106dc20a4c23 Mon Sep 17 00:00:00 2001 From: Ben McKeegan Date: Mon, 16 Nov 2009 03:44:25 +0000 Subject: [PATCH] ppp: fix BUG on non-linear SKB (multilink receive) 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 Signed-off-by: David S. Miller --- drivers/net/ppp_generic.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-) diff --git a/drivers/net/ppp_generic.c b/drivers/net/ppp_generic.c index 9bf2a6be903..965adb6174c 100644 --- a/drivers/net/ppp_generic.c +++ b/drivers/net/ppp_generic.c @@ -1944,8 +1944,15 @@ ppp_receive_mp_frame(struct ppp *ppp, struct sk_buff *skb, struct channel *pch) } /* 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;