From bc52413756bd663607606291492403b51140a1d2 Mon Sep 17 00:00:00 2001
From: Adrian Ratiu <adrian.ratiu@collabora.com>
Date: Tue, 16 Feb 2021 20:06:02 +0200
Subject: [PATCH] pppd: Add option to avoid IP/route configuration

---
 pppd/ipcp.c | 29 +++++++++++++++++++++--------
 1 file changed, 21 insertions(+), 8 deletions(-)

diff --git a/pppd/ipcp.c b/pppd/ipcp.c
index 302ca40..5198ad9 100644
--- a/pppd/ipcp.c
+++ b/pppd/ipcp.c
@@ -88,6 +88,7 @@ struct notifier *ip_down_notifier = NULL;
 /* local vars */
 static int default_route_set[NUM_PPP];	/* Have set up a default route */
 static int proxy_arp_set[NUM_PPP];	/* Have created proxy arp entry */
+static bool neg_systemconfig;		/* Skip system configuration */
 static bool usepeerdns;			/* Ask peer for DNS addrs */
 static int ipcp_is_up;			/* have called np_up() */
 static int ipcp_is_open;		/* haven't called np_finished() */
@@ -217,6 +218,9 @@ static option_t ipcp_option_list[] = {
     { "usepeerdns", o_bool, &usepeerdns,
       "Ask peer for DNS address(es)", 1 },
 
+    { "nosystemconfig", o_bool, &neg_systemconfig,
+      "Avoid IP and route configuration of ppp device", 1 },
+
     { "netmask", o_special, (void *)setnetmask,
       "set netmask", OPT_PRIO | OPT_A2STRVAL | OPT_STATIC, netmask_str },
 
@@ -1792,7 +1796,8 @@ ipcp_up(fsm *f)
 	script_setenv("DNS2", ip_ntoa(go->dnsaddr[1]), 0);
     if (usepeerdns && (go->dnsaddr[0] || go->dnsaddr[1])) {
 	script_setenv("USEPEERDNS", "1", 0);
-	create_resolv(go->dnsaddr[0], go->dnsaddr[1]);
+	if (!neg_systemconfig)
+	    create_resolv(go->dnsaddr[0], go->dnsaddr[1]);
     }
 
     /*
@@ -1859,8 +1864,12 @@ ipcp_up(fsm *f)
 	 */
 	mask = GetMask(go->ouraddr);
 
+	if (neg_systemconfig && debug)
+		warn("Avoiding system configuration by request");
+
 #if !(defined(SVR4) && (defined(SNI) || defined(__USLC__)))
-	if (!sifaddr(f->unit, go->ouraddr, ho->hisaddr, mask)) {
+	if (!neg_systemconfig &&
+	    !sifaddr(f->unit, go->ouraddr, ho->hisaddr, mask)) {
 	    if (debug)
 		warn("Interface configuration failed");
 	    ipcp_close(f->unit, "Interface configuration failed");
@@ -1881,7 +1890,7 @@ ipcp_up(fsm *f)
 	}
 
 	/* bring the interface up for IP */
-	if (!sifup(f->unit)) {
+	if (!neg_systemconfig && !sifup(f->unit)) {
 	    if (debug)
 		warn("Interface failed to come up");
 	    ipcp_close(f->unit, "Interface configuration failed");
@@ -1889,7 +1898,8 @@ ipcp_up(fsm *f)
 	}
 
 #if (defined(SVR4) && (defined(SNI) || defined(__USLC__)))
-	if (!sifaddr(f->unit, go->ouraddr, ho->hisaddr, mask)) {
+	if (!neg_systemconfig &&
+	    !sifaddr(f->unit, go->ouraddr, ho->hisaddr, mask)) {
 	    if (debug)
 		warn("Interface configuration failed");
 	    ipcp_close(f->unit, "Interface configuration failed");
@@ -1899,13 +1909,14 @@ ipcp_up(fsm *f)
 	sifnpmode(f->unit, PPP_IP, NPMODE_PASS);
 
 	/* assign a default route through the interface if required */
-	if (ipcp_wantoptions[f->unit].default_route) 
+	if (!neg_systemconfig && ipcp_wantoptions[f->unit].default_route)
 	    if (sifdefaultroute(f->unit, go->ouraddr, ho->hisaddr,
 					 wo->replace_default_route))
 		default_route_set[f->unit] = 1;
 
 	/* Make a proxy ARP entry if requested. */
-	if (ho->hisaddr != 0 && ipcp_wantoptions[f->unit].proxy_arp)
+	if (!neg_systemconfig &&
+	    ho->hisaddr != 0 && ipcp_wantoptions[f->unit].proxy_arp)
 	    if (sifproxyarp(f->unit, ho->hisaddr))
 		proxy_arp_set[f->unit] = 1;
 
@@ -1976,7 +1987,8 @@ ipcp_down(fsm *f)
 	sifnpmode(f->unit, PPP_IP, NPMODE_QUEUE);
     } else {
 	sifnpmode(f->unit, PPP_IP, NPMODE_DROP);
-	sifdown(f->unit);
+	if (!neg_systemconfig)
+	    sifdown(f->unit);
 	ipcp_clear_addrs(f->unit, ipcp_gotoptions[f->unit].ouraddr,
 			 ipcp_hisoptions[f->unit].hisaddr, 0);
     }
@@ -2012,7 +2024,8 @@ ipcp_clear_addrs(int unit, u_int32_t ouraddr, u_int32_t hisaddr, bool replacedef
 	cifdefaultroute(unit, ouraddr, hisaddr);
 	default_route_set[unit] = 0;
     }
-    cifaddr(unit, ouraddr, hisaddr);
+    if (!neg_systemconfig)
+	cifaddr(unit, ouraddr, hisaddr);
 }
 
 
-- 
2.30.1