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l2tp: Add protocol field decompression

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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>
This commit is contained in:
Sam Protsenko 2018-12-14 19:59:21 +02:00 committed by David S. Miller
parent 63de273f34
commit c151acc6e9
1 changed files with 4 additions and 0 deletions
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4
net/l2tp/l2tp_ppp.c
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@ -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;