From b81956418ca6590d8c3b1a6758dccc0f2f05eb54 Mon Sep 17 00:00:00 2001
From: Jaco Kroon <jaco@uls.co.za>
Date: Tue, 18 Oct 2022 12:46:11 +0200
Subject: [PATCH] Pass remotenumber to pppd.

By default this will be the IP address of the remote peer, but it could
be the remote's number as provided by way of AVP should the newly added
'trust remotenumber' LNS option be set to yes.

Signed-off-by: Jaco Kroon <jaco@uls.co.za>
---
 doc/l2tpd.conf.sample |  1 +
 doc/xl2tpd.conf.5     |  6 ++++++
 file.c                | 17 +++++++++++++++++
 file.h                |  1 +
 xl2tpd.c              |  8 ++++++++
 5 files changed, 33 insertions(+)

diff --git a/doc/l2tpd.conf.sample b/doc/l2tpd.conf.sample
index 8f8fcb5..f6f0359 100644
--- a/doc/l2tpd.conf.sample
+++ b/doc/l2tpd.conf.sample
@@ -47,6 +47,7 @@
 ; rx bps = 10000000				; Receive tunnel speed
 ; tx bps = 10000000				; Transmit tunnel speed
 ; bps = 100000					; Define both receive and transmit speed in one option
+; trust remotenumber = no			; Trust dialing number AVP?
 
 ; [lac marko]							; Example VPN LAC definition
 ; lns = lns.marko.net					; * Who is our LNS?
diff --git a/doc/xl2tpd.conf.5 b/doc/xl2tpd.conf.5
index 2b1acbc..173a453 100644
--- a/doc/xl2tpd.conf.5
+++ b/doc/xl2tpd.conf.5
@@ -175,6 +175,12 @@ This will enable the debug for pppd.
 .B pass peer
 Pass the peer's IP address to pppd as ipparam. Enabled by default.
 
+.TP
+.B trust remotenumber
+When this is set to yes xl2tpd will trust the dialing number AVP and provide
+that as the remotenumber to pppd rather than the peer's IP address.  Default is
+not trusted.
+
 .TP 
 .B pppoptfile
 Specify the path for a file which contains pppd configuration parameters
diff --git a/file.c b/file.c
index 17dc377..29fcb66 100644
--- a/file.c
+++ b/file.c
@@ -676,6 +676,22 @@ int set_pass_peer (char *word, char *value, int context, void *item)
     return 0;
 }
 
+int set_trust_remotenumber (char *word, char *value, int context, void *item)
+{
+    switch (context & ~CONTEXT_DEFAULT)
+    {
+    case CONTEXT_LNS:
+        if (set_boolean (word, value, &(((struct lns *) item)->trust_remotenumber)))
+            return -1;
+        break;
+    default:
+        snprintf (filerr, sizeof (filerr), "'%s' not valid in this context\n",
+                  word);
+        return -1;
+    }
+    return 0;
+}
+
 int set_pppoptfile (char *word, char *value, int context, void *item)
 {
     struct lac *l = (struct lac *) item;
@@ -1611,6 +1627,7 @@ struct keyword words[] = {
     {"hostname", &set_hostname},
     {"ppp debug", &set_debug},
     {"pass peer", &set_pass_peer},
+    {"trust remotenumber", &set_trust_remotenumber},
     {"pppoptfile", &set_pppoptfile},
     {"call rws", &set_rws},
     {"tunnel rws", &set_rws},
diff --git a/file.h b/file.h
index a2707c2..9d76359 100644
--- a/file.h
+++ b/file.h
@@ -97,6 +97,7 @@ struct lns
     int proxyauth;              /* Allow proxy authentication? */
     int debug;                  /* Debug PPP? */
     int pass_peer;              /* Pass peer IP to pppd as ipparam? */
+    int trust_remotenumber;     /* Whether or not to trust remotely supplied "Dialing Number" AVP */
     char pppoptfile[STRLEN];    /* File containing PPP options */
     struct tunnel *t;           /* Tunnel of this, if it's ready */
 };
diff --git a/xl2tpd.c b/xl2tpd.c
index 3195988..b551146 100644
--- a/xl2tpd.c
+++ b/xl2tpd.c
@@ -495,6 +495,14 @@ int start_pppd (struct call *c, struct ppp_opts *opts)
     }
 
     {
+        stropt[pos++] = strdup("remotenumber");
+        if (c->dialing[0] && (!c->lns || c->lns->trust_remotenumber)) {
+            /* if a remotenumber is available, and we're a LAC or the remote "dialing number" AVP is trusted */
+            stropt[pos++] = strdup(c->dialing);
+        } else {
+            stropt[pos++] = strdup(IPADDY(c->container->peer.sin_addr));
+        }
+
         struct ppp_opts *p = opts;
         int maxn_opts = sizeof(stropt) / sizeof(stropt[0]) - 1;
         while (p && pos < maxn_opts)
-- 
2.44.2