From: pali <7141871+pali@users.noreply.github.com>
Date: Tue, 26 Jan 2021 02:55:25 +0000 (+0100)
Subject: pppd: Negotiate IP address when only peer addresses are provided (#236)
X-Git-Tag: ppp-2.5.0~93
X-Git-Url: https://git.ozlabs.org/?a=commitdiff_plain;h=a2094eba2406392a7bb69b436155e2d08ea555e8;p=ppp.git

pppd: Negotiate IP address when only peer addresses are provided (#236)

This fixes special case when both ppp ends are configured to send only IP
address of other side and do not send its own IP address. Such setup is
correct because both ends can exchange its IP addresses and therefore they
have full information, they known both local and remote address.

This issue can be triggered by calling pppd with arguments:

    ./pppd debug local noauth nolock nodetach asyncmap 0 default-asyncmap novj noaccomp nopcomp nodeflate nobsdcomp nomagic noipv6 noipdefault nosendip :10.0.0.1 pty "./pppd debug local noauth nolock nodetach asyncmap 0 default-asyncmap novj noaccomp nopcomp nodeflate nobsdcomp nomagic noipv6 nosendip nodefaultroute :10.0.0.2 notty"

Without this patch IP addresses are not exchanges at all and pppd fails:

    rcvd [LCP ConfReq id=0x1]
    sent [LCP ConfReq id=0x1]
    sent [LCP ConfAck id=0x1]
    rcvd [LCP ConfAck id=0x1]
    sent [LCP EchoReq id=0x0 magic=0x0]
    sent [IPCP ConfReq id=0x1]
    rcvd [LCP EchoReq id=0x0 magic=0x0]
    sent [LCP EchoRep id=0x0 magic=0x0]
    rcvd [IPCP ConfReq id=0x1]
    sent [IPCP ConfAck id=0x1]
    rcvd [LCP EchoRep id=0x0 magic=0x0]
    rcvd [IPCP ConfAck id=0x1]
    Could not determine local IP address

After applying this patch exchanging of IP addresses is working fine:

    rcvd [LCP ConfReq id=0x1]
    sent [LCP ConfReq id=0x1]
    sent [LCP ConfAck id=0x1]
    rcvd [LCP ConfAck id=0x1]
    sent [LCP EchoReq id=0x0 magic=0x0]
    sent [IPCP ConfReq id=0x1]
    rcvd [LCP EchoReq id=0x0 magic=0x0]
    sent [LCP EchoRep id=0x0 magic=0x0]
    rcvd [IPCP ConfReq id=0x1]
    sent [IPCP ConfNak id=0x1 <addr 10.0.0.1>]
    rcvd [LCP EchoRep id=0x0 magic=0x0]
    rcvd [IPCP ConfNak id=0x1 <addr 10.0.0.2>]
    sent [IPCP ConfReq id=0x2 <addr 10.0.0.2>]
    rcvd [IPCP ConfReq id=0x2 <addr 10.0.0.1>]
    sent [IPCP ConfAck id=0x2 <addr 10.0.0.1>]
    rcvd [IPCP ConfAck id=0x2 <addr 10.0.0.2>]
    local  IP address 10.0.0.2
    remote IP address 10.0.0.1

Signed-off-by: Pali Rohár <pali@kernel.org>
---

diff --git a/pppd/ipcp.c b/pppd/ipcp.c
index fcf17b1..d17dbd2 100644
--- a/pppd/ipcp.c
+++ b/pppd/ipcp.c
@@ -678,8 +678,9 @@ ipcp_resetci(fsm *f)
     ipcp_options *go = &ipcp_gotoptions[f->unit];
     ipcp_options *ao = &ipcp_allowoptions[f->unit];
 
-    wo->req_addr = (wo->neg_addr || wo->old_addrs) &&
-	(ao->neg_addr || ao->old_addrs);
+    wo->req_addr = ((wo->neg_addr || wo->old_addrs) &&
+	(ao->neg_addr || ao->old_addrs)) ||
+	(wo->hisaddr && !wo->accept_remote);
     if (wo->ouraddr == 0)
 	wo->accept_local = 1;
     if (wo->hisaddr == 0)
@@ -1648,7 +1649,8 @@ endswitch:
      * option safely.
      */
     if (rc != CONFREJ && !ho->neg_addr && !ho->old_addrs &&
-	wo->req_addr && !reject_if_disagree && !noremoteip) {
+	wo->req_addr && !reject_if_disagree &&
+	((wo->hisaddr && !wo->accept_remote) || !noremoteip)) {
 	if (rc == CONFACK) {
 	    rc = CONFNAK;
 	    ucp = inp;			/* reset pointer */