pppd: Add replacedefaultroute option (#200)

Adds an option to pppd to control whether to replace existing default routes
when using the 'defaultroute' option.

If defaultroute and replacedefaultroute are both set, pppd replaces an existing
default route with the new default route. The old default route is restored when
the connection is taken down.

Signed-off-by: Samuel Thibault <samuel.thibault@ens-lyon.org>
Co-authored-by: Chris Boot <bootc@debian.org>

diff --git a/pppd/ipcp.c b/pppd/ipcp.c
index f8942a9645592ad7961b2555f8c8fd0393f23c1d..302ca40b4c83cecce9098bfff17dfe75b0bedba0 100644 (file)
--- a/pppd/ipcp.c
+++ b/pppd/ipcp.c
@@ -196,6 +196,15 @@ static option_t ipcp_option_list[] = {
       "disable defaultroute option", OPT_ALIAS | OPT_A2CLR,
       &ipcp_wantoptions[0].default_route },
 
+#ifdef __linux__
+    { "replacedefaultroute", o_bool,
+                               &ipcp_wantoptions[0].replace_default_route,
+      "Replace default route", OPT_PRIV | 1
+    },
+    { "noreplacedefaultroute", o_bool,
+                               &ipcp_wantoptions[0].replace_default_route,
+      "Do not replace default route", 0 },
+#endif
     { "proxyarp", o_bool, &ipcp_wantoptions[0].proxy_arp,
       "Add proxy ARP entry", OPT_ENABLE|1, &ipcp_allowoptions[0].proxy_arp },
     { "noproxyarp", o_bool, &ipcp_allowoptions[0].proxy_arp,
@@ -269,7 +278,7 @@ struct protent ipcp_protent = {
     ip_active_pkt
 };
 
-static void ipcp_clear_addrs (int, u_int32_t, u_int32_t);
+static void ipcp_clear_addrs (int, u_int32_t, u_int32_t, bool);
 static void ipcp_script (char *, int); /* Run an up/down script */
 static void ipcp_script_done (void *);
 
@@ -1716,7 +1725,8 @@ ip_demand_conf(int u)
     if (!sifnpmode(u, PPP_IP, NPMODE_QUEUE))
        return 0;
     if (wo->default_route)
-       if (sifdefaultroute(u, wo->ouraddr, wo->hisaddr))
+       if (sifdefaultroute(u, wo->ouraddr, wo->hisaddr,
+                                           wo->replace_default_route))
            default_route_set[u] = 1;
     if (wo->proxy_arp)
        if (sifproxyarp(u, wo->hisaddr))
@@ -1804,7 +1814,8 @@ ipcp_up(fsm *f)
      */
     if (demand) {
        if (go->ouraddr != wo->ouraddr || ho->hisaddr != wo->hisaddr) {
-           ipcp_clear_addrs(f->unit, wo->ouraddr, wo->hisaddr);
+           ipcp_clear_addrs(f->unit, wo->ouraddr, wo->hisaddr,
+                                     wo->replace_default_route);
            if (go->ouraddr != wo->ouraddr) {
                warn("Local IP address changed to %I", go->ouraddr);
                script_setenv("OLDIPLOCAL", ip_ntoa(wo->ouraddr), 0);
@@ -1829,7 +1840,8 @@ ipcp_up(fsm *f)
 
            /* assign a default route through the interface if required */
            if (ipcp_wantoptions[f->unit].default_route) 
-               if (sifdefaultroute(f->unit, go->ouraddr, ho->hisaddr))
+               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. */
@@ -1888,7 +1900,8 @@ ipcp_up(fsm *f)
 
        /* assign a default route through the interface if required */
        if (ipcp_wantoptions[f->unit].default_route) 
-           if (sifdefaultroute(f->unit, go->ouraddr, ho->hisaddr))
+           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. */
@@ -1965,7 +1978,7 @@ ipcp_down(fsm *f)
        sifnpmode(f->unit, PPP_IP, NPMODE_DROP);
        sifdown(f->unit);
        ipcp_clear_addrs(f->unit, ipcp_gotoptions[f->unit].ouraddr,
-                        ipcp_hisoptions[f->unit].hisaddr);
+                        ipcp_hisoptions[f->unit].hisaddr, 0);
     }
 
     /* Execute the ip-down script */
@@ -1981,13 +1994,21 @@ ipcp_down(fsm *f)
  * proxy arp entries, etc.
  */
 static void
-ipcp_clear_addrs(int unit, u_int32_t ouraddr, u_int32_t hisaddr)
+ipcp_clear_addrs(int unit, u_int32_t ouraddr, u_int32_t hisaddr, bool replacedefaultroute)
 {
     if (proxy_arp_set[unit]) {
        cifproxyarp(unit, hisaddr);
        proxy_arp_set[unit] = 0;
     }
-    if (default_route_set[unit]) {
+    /* If replacedefaultroute, sifdefaultroute will be called soon
+     * with replacedefaultroute set and that will overwrite the current
+     * default route. This is the case only when doing demand, otherwise
+     * during demand, this cifdefaultroute would restore the old default
+     * route which is not what we want in this case. In the non-demand
+     * case, we'll delete the default route and restore the old if there
+     * is one saved by an sifdefaultroute with replacedefaultroute.
+     */
+    if (!replacedefaultroute && default_route_set[unit]) {
        cifdefaultroute(unit, ouraddr, hisaddr);
        default_route_set[unit] = 0;
     }

diff --git a/pppd/ipcp.h b/pppd/ipcp.h
index dc6665cf0cd7c731151704d36a768fdbf2546e06..9c4f68df2b862d8d0a28c17aa5bd741515f8dba8 100644 (file)
--- a/pppd/ipcp.h
+++ b/pppd/ipcp.h
@@ -68,6 +68,7 @@ typedef struct ipcp_options {
     bool old_addrs;            /* Use old (IP-Addresses) option? */
     bool req_addr;             /* Ask peer to send IP address? */
     bool default_route;                /* Assign default route through interface? */
+    bool replace_default_route;        /* Replace default route through interface? */
     bool proxy_arp;            /* Make proxy ARP entry for peer? */
     bool neg_vj;               /* Van Jacobson Compression? */
     bool old_vj;               /* use old (short) form of VJ option? */

diff --git a/pppd/pppd.8 b/pppd/pppd.8
index 3b7c28835cd9b87c5a3051029e7b28fbc8d296fc..bb7e2ff1d80732263c6ce2ca33c679ba0f064970 100644 (file)
--- a/pppd/pppd.8
+++ b/pppd/pppd.8
@@ -133,6 +133,11 @@ the gateway, when IPv6CP negotiation is successfully completed.
 This entry is removed when the PPP connection is broken.  This option
 is privileged if the \fInodefaultroute6\fR option has been specified.
 .TP
+.B replacedefaultroute
+This option is a flag to the defaultroute option. If defaultroute is
+set and this flag is also set, pppd replaces an existing default route
+with the new default route.  This option is privileged.
+.TP
 .B disconnect \fIscript
 Execute the command specified by \fIscript\fR, by passing it to a
 shell, after
@@ -792,9 +797,13 @@ disable both forms of hardware flow control.
 .TP
 .B nodefaultroute
 Disable the \fIdefaultroute\fR option.  The system administrator who
-wishes to prevent users from creating default routes with pppd
+wishes to prevent users from adding a default route with pppd
 can do so by placing this option in the /etc/ppp/options file.
 .TP
+.B noreplacedefaultroute
+Disable the \fIreplacedefaultroute\fR option. This allows to disable a
+\fIreplacedefaultroute\fR option set previously in the configuration.
+.TP
 .B nodefaultroute6
 Disable the \fIdefaultroute6\fR option.  The system administrator who
 wishes to prevent users from adding a default route with pppd

diff --git a/pppd/pppd.h b/pppd/pppd.h
index 9f5f1ae07683d8ee45b77433399b3a4c16bd5b41..6ac0ab83e51754d9df69bdc5c69a6b303ec4138b 100644 (file)
--- a/pppd/pppd.h
+++ b/pppd/pppd.h
@@ -679,7 +679,7 @@ int  sif6addr(int, eui64_t, eui64_t);
 int  cif6addr(int, eui64_t, eui64_t);
                                /* Remove an IPv6 address from i/f */
 #endif
-int  sifdefaultroute(int, u_int32_t, u_int32_t);
+int  sifdefaultroute(int, u_int32_t, u_int32_t, bool replace_default_rt);
                                /* Create default route through i/f */
 int  cifdefaultroute(int, u_int32_t, u_int32_t);
                                /* Delete default route through i/f */

diff --git a/pppd/sys-linux.c b/pppd/sys-linux.c
index 6106467cc9844451f41764fead9cc2b4210ffabf..8b538f0e4ac4431688ac421b7c622032d3f7589f 100644 (file)
--- a/pppd/sys-linux.c
+++ b/pppd/sys-linux.c
@@ -209,6 +209,8 @@ static int  if_is_up;       /* Interface has been marked up */
 static int     if6_is_up;      /* Interface has been marked up for IPv6, to help differentiate */
 static int     have_default_route;     /* Gateway for default route added */
 static int     have_default_route6;    /* Gateway for default IPv6 route added */
+static struct  rtentry old_def_rt;     /* Old default route */
+static int     default_rt_repl_rest;   /* replace and restore old default rt */
 static u_int32_t proxy_arp_addr;       /* Addr for proxy arp entry added */
 static char proxy_arp_dev[16];         /* Device for proxy arp entry */
 static u_int32_t our_old_addr;         /* for detecting address changes */
@@ -1573,6 +1575,9 @@ static int read_route_table(struct rtentry *rt)
        p = NULL;
     }
 
+    SET_SA_FAMILY (rt->rt_dst,     AF_INET);
+    SET_SA_FAMILY (rt->rt_gateway, AF_INET);
+
     SIN_ADDR(rt->rt_dst) = strtoul(cols[route_dest_col], NULL, 16);
     SIN_ADDR(rt->rt_gateway) = strtoul(cols[route_gw_col], NULL, 16);
     SIN_ADDR(rt->rt_genmask) = strtoul(cols[route_mask_col], NULL, 16);
@@ -1645,20 +1650,53 @@ int have_route_to(u_int32_t addr)
 /********************************************************************
  *
  * sifdefaultroute - assign a default route through the address given.
+ *
+ * If the global default_rt_repl_rest flag is set, then this function
+ * already replaced the original system defaultroute with some other
+ * route and it should just replace the current defaultroute with
+ * another one, without saving the current route. Use: demand mode,
+ * when pppd sets first a defaultroute it it's temporary ppp0 addresses
+ * and then changes the temporary addresses to the addresses for the real
+ * ppp connection when it has come up.
  */
 
-int sifdefaultroute (int unit, u_int32_t ouraddr, u_int32_t gateway)
+int sifdefaultroute (int unit, u_int32_t ouraddr, u_int32_t gateway, bool replace)
 {
-    struct rtentry rt;
+    struct rtentry rt, tmp_rt;
+    struct rtentry *del_rt = NULL;
 
-    if (defaultroute_exists(&rt, dfl_route_metric) && strcmp(rt.rt_dev, ifname) != 0) {
-       if (rt.rt_flags & RTF_GATEWAY)
-           error("not replacing existing default route via %I with metric %d",
-                 SIN_ADDR(rt.rt_gateway), dfl_route_metric);
-       else
-           error("not replacing existing default route through %s with metric %d",
-                 rt.rt_dev, dfl_route_metric);
-       return 0;
+    if (default_rt_repl_rest) {
+       /* We have already replaced the original defaultroute, if we
+        * are called again, we will delete the current default route
+        * and set the new default route in this function.
+        * - this is normally only the case the doing demand: */
+       if (defaultroute_exists(&tmp_rt, -1))
+           del_rt = &tmp_rt;
+    } else if (defaultroute_exists(&old_def_rt, -1           ) &&
+                           strcmp( old_def_rt.rt_dev, ifname) != 0) {
+       /*
+        * We did not yet replace an existing default route, let's
+        * check if we should save and replace a default route:
+        */
+       u_int32_t old_gateway = SIN_ADDR(old_def_rt.rt_gateway);
+
+       if (old_gateway != gateway) {
+           if (!replace) {
+               error("not replacing default route to %s [%I]",
+                       old_def_rt.rt_dev, old_gateway);
+               return 0;
+           } else {
+               /* we need to copy rt_dev because we need it permanent too: */
+               char * tmp_dev = malloc(strlen(old_def_rt.rt_dev)+1);
+               strcpy(tmp_dev, old_def_rt.rt_dev);
+               old_def_rt.rt_dev = tmp_dev;
+
+               notice("replacing old default route to %s [%I]",
+                       old_def_rt.rt_dev, old_gateway);
+               default_rt_repl_rest = 1;
+               del_rt = &old_def_rt;
+           }
+       }
     }
 
     memset (&rt, 0, sizeof (rt));
@@ -1678,6 +1716,12 @@ int sifdefaultroute (int unit, u_int32_t ouraddr, u_int32_t gateway)
            error("default route ioctl(SIOCADDRT): %m");
        return 0;
     }
+    if (default_rt_repl_rest && del_rt)
+       if (ioctl(sock_fd, SIOCDELRT, del_rt) < 0) {
+           if ( ! ok_error ( errno ))
+               error("del old default route ioctl(SIOCDELRT): %m(%d)", errno);
+           return 0;
+       }
 
     have_default_route = 1;
     return 1;
@@ -1716,6 +1760,16 @@ int cifdefaultroute (int unit, u_int32_t ouraddr, u_int32_t gateway)
            return 0;
        }
     }
+    if (default_rt_repl_rest) {
+       notice("restoring old default route to %s [%I]",
+                       old_def_rt.rt_dev, SIN_ADDR(old_def_rt.rt_gateway));
+       if (ioctl(sock_fd, SIOCADDRT, &old_def_rt) < 0) {
+           if ( ! ok_error ( errno ))
+               error("restore default route ioctl(SIOCADDRT): %m(%d)", errno);
+           return 0;
+       }
+       default_rt_repl_rest = 0;
+    }
 
     return 1;
 }

diff --git a/pppd/sys-solaris.c b/pppd/sys-solaris.c
index 7e3a7e96debdfe52bff51c58cdb93b756060d34e..24c3776eb111eaaaf5e69fecf45e4c5a8af12079 100644 (file)
--- a/pppd/sys-solaris.c
+++ b/pppd/sys-solaris.c
@@ -2038,10 +2038,15 @@ cifaddr(int u, u_int32_t o, u_int32_t h)
  * sifdefaultroute - assign a default route through the address given.
  */
 int
-sifdefaultroute(int u, u_int32_t l, u_int32_t g)
+sifdefaultroute(int u, u_int32_t l, u_int32_t g, bool replace)
 {
     struct rtentry rt;
 
+    if (replace) {
+       error("Replacing the default route is not implemented on Solaris yet");
+       return 0;
+    }
+
 #if defined(__USLC__)
     g = l;                     /* use the local address as gateway */
 #endif