Commit 82b3cc1a authored by Ben McKeegan's avatar Ben McKeegan Committed by David S. Miller
Browse files

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: default avatarBen McKeegan <>
Signed-off-by: default avatarDavid S. Miller <>
parent c0e1f68b
......@@ -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 {
Markdown is supported
0% or .
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment