ppp: update interface name in the plugin after NM changes itbg/bgo1515829

When NM knows of the ifindex/name of the new PPP interface (through
the SetIfindex() call), it renames it. This can race with the pppd
daemon, which issues ioctl() using the interface name cached in the
global 'ifname' variable:

  ...
  NetworkManager[27213]: <debug> [1515427406.0036] ppp-manager: set-ifindex 71
  pppd[27801]: sent [CCP ConfRej id=0x1 <deflate 15> <deflate(old#) 15> <bsd v1 15>]
  NetworkManager[27213]: <debug> [1515427406.0036] platform: link: setting 'ppp5' (71) name dsl-ppp
  pppd[27801]: sent [IPCP ConfAck id=0x2 <addr 3.1.1.1>]
  pppd[27801]: ioctl(SIOCSIFADDR): No such device (line 2473)
  pppd[27801]: Interface configuration failed
  pppd[27801]: Couldn't get PPP statistics: No such device
  ...

Fortunately the variable is exposed to plugins and so we can turn the
SetIfindex() D-Bus call into a synchronous one and then update the
value of the 'ifname' global variable with the new interface name
assigned by NM.

1 files changed, 18 insertions, 6 deletions

diff --git a/src/ppp/nm-pppd-plugin.c b/src/ppp/nm-pppd-plugin.c
index eabb3afb79..b0210595e3 100644
--- a/src/ppp/nm-pppd-plugin.c
+++ b/src/ppp/nm-pppd-plugin.c
@@ -52,6 +52,8 @@ nm_phasechange (void *data, int arg)
 {
 	NMPPPStatus ppp_status = NM_PPP_STATUS_UNKNOWN;
 	char *ppp_phase;
+	int index;
+	char new_name[IF_NAMESIZE];
 
 	g_return_if_fail (G_IS_DBUS_PROXY (proxy));
 
@@ -129,12 +131,22 @@ nm_phasechange (void *data, int arg)
 	}
 
 	if (ppp_status == PHASE_RUNNING) {
-		g_dbus_proxy_call (proxy,
-		                   "SetIfindex",
-		                   g_variant_new ("(i)", if_nametoindex (ifname)),
-		                   G_DBUS_CALL_FLAGS_NONE, -1,
-		                   NULL,
-		                   NULL, NULL);
+		index = if_nametoindex (ifname);
+		/* Make a sync call to ensure that when the call
+		 * terminates the interface already has its final
+		 * name. */
+		g_dbus_proxy_call_sync (proxy,
+		                        "SetIfindex",
+		                        g_variant_new ("(i)", index),
+		                        G_DBUS_CALL_FLAGS_NONE,
+		                        25000,
+		                        NULL, NULL);
+		/* Update the name in pppd if NM changed it */
+		if (   if_indextoname (index, new_name)
+		    && !nm_streq0 (ifname, new_name)) {
+			g_message ("nm-ppp-plugin: interface name changed from '%s' to '%s'", ifname, new_name);
+			strncpy (ifname, new_name, IF_NAMESIZE);
+		}
 	}
 }