From c151acc6e9ffa08972aa20d8bc07a66081922c1e Mon Sep 17 00:00:00 2001 From: Sam Protsenko Date: Fri, 14 Dec 2018 19:59:21 +0200 Subject: [PATCH] l2tp: Add protocol field decompression When Protocol Field Compression (PFC) is enabled, the "Protocol" field in PPP packet will be received without leading 0x00. See section 6.5 in RFC 1661 for details. So let's decompress protocol field if needed, the same way it's done in drivers/net/ppp/pptp.c. In case when "nopcomp" pppd option is not enabled, PFC (pcomp) can be negotiated during LCP handshake, and L2TP driver in kernel will receive PPP packets with compressed Protocol field, which in turn leads to next error: Protocol Rejected (unsupported protocol 0x2145) because instead of Protocol=0x0021 in PPP packet there will be Protocol=0x21. This patch unwraps it back to 0x0021, which fixes the issue. Sending the compressed Protocol field will be implemented in subsequent patch, this one is self-sufficient. Signed-off-by: Sam Protsenko Signed-off-by: David S. Miller --- net/l2tp/l2tp_ppp.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/net/l2tp/l2tp_ppp.c b/net/l2tp/l2tp_ppp.c index 04d9946dcdba..c03c6461f236 100644 --- a/net/l2tp/l2tp_ppp.c +++ b/net/l2tp/l2tp_ppp.c @@ -236,6 +236,10 @@ static void pppol2tp_recv(struct l2tp_session *session, struct sk_buff *skb, int skb->data[1] == PPP_UI) skb_pull(skb, 2); + /* Decompress protocol field if PFC is enabled */ + if ((*skb->data) & 0x1) + *(u8 *)skb_push(skb, 1) = 0; + if (sk->sk_state & PPPOX_BOUND) { struct pppox_sock *po;