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PPP, PPPoL2TP: drop unexpected packets from peer

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Conform a little bit more to the RFC by dropping duplicate received
packets. It might help discover Ns sequence issues.

Signed-off-by: Sylvain Rochet <gradator@gradator.net>
This commit is contained in:
Sylvain Rochet 2018-06-15 13:51:56 +02:00
parent 047c3c6528
commit a56519032e
1 changed files with 15 additions and 3 deletions
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18
src/netif/ppp/pppol2tp.c
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@ -268,7 +268,7 @@ static void pppol2tp_connect(ppp_pcb *ppp, void *ctx) {
l2tp->tunnel_port = l2tp->remote_port;
l2tp->our_ns = 0;
l2tp->peer_nr = 0;
l2tp->peer_ns = 0;
l2tp->peer_ns = ~0; /* First expected packet is 0 */
l2tp->source_tunnel_id = 0;
l2tp->remote_tunnel_id = 0;
l2tp->source_session_id = 0;
@ -493,10 +493,20 @@ static void pppol2tp_dispatch_control_packet(pppol2tp_pcb *l2tp, u16_t port, str
u8_t challenge_id = 0;
#endif /* PPPOL2TP_AUTH_SUPPORT */
l2tp->peer_nr = nr;
l2tp->peer_ns = ns;
/* printf("L2TP CTRL INPUT, ns=%d, nr=%d, len=%d\n", ns, nr, p->len); */
/* Drop unexpected packet */
if (ns != (u16_t)(l2tp->peer_ns+1)) {
PPPDEBUG(LOG_DEBUG, ("pppol2tp: drop unexpected packet: received NS=%d, expected NS=%d\n", ns, l2tp->peer_ns+1));
/*
* The RFC says we must send a ZLB ack for duplicate packets but preventing an endless
* ZLB packets loop came out wayyyy more complicated than just dropping the packet.
*/
return;
}
l2tp->peer_nr = nr;
/* Handle the special case of the ICCN acknowledge */
if (l2tp->phase == PPPOL2TP_STATE_ICCN_SENT && (s16_t)(l2tp->peer_nr - l2tp->our_ns) > 0) {
l2tp->phase = PPPOL2TP_STATE_DATA;
@ -507,6 +517,8 @@ static void pppol2tp_dispatch_control_packet(pppol2tp_pcb *l2tp, u16_t port, str
if (p->tot_len == 0) {
return;
}
/* A ZLB packet does not consume a NS slot thus we don't record the NS value for ZLB packets */
l2tp->peer_ns = ns;
p = pbuf_coalesce(p, PBUF_RAW);
inp = (u8_t*)p->payload;