Commit c151acc6 authored Dec 14, 2018 by Sam Protsenko Committed by David S. Miller Dec 15, 2018

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 <semen.protsenko@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent 63de273f

net/l2tp/l2tp_ppp.c

+4 −0

Original line number	Diff line number	Diff line
		@@ -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;

Admin message