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PPP, MPPE, discard late packet in stateless mode

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When PPP is used over a link which does not guarantee packet ordering,
we might get late MPPE packets. This is a problem because MPPE must be
kept synchronized and the current implementation does not drop them and
rekey 4095 times instead of 0, which is wrong.

In order to prevent rekeying about a whole count space times (~ 4095
times), drop packets which are not within the forward 4096/2 window and
increase sanity error counter.
This commit is contained in:
Sylvain Rochet 2015-04-26 20:59:09 +02:00
parent d0f91c00cb
commit adaeff5540
1 changed files with 6 additions and 0 deletions
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6
src/netif/ppp/mppe.c
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@ -308,6 +308,12 @@ mppe_decompress(ppp_pcb *pcb, ppp_mppe_state *state, struct pbuf **pb)
*/
if (!state->stateful) {
/* Discard late packet */
if ((ccount - state->ccount) % MPPE_CCOUNT_SPACE > MPPE_CCOUNT_SPACE / 2) {
state->sanity_errors++;
goto sanity_error;
}
/* RFC 3078, sec 8.1. Rekey for every packet. */
while (state->ccount != ccount) {
mppe_rekey(state, 0);