core: ppp: use a different unit for each activation

We can't tell pppd to create an interface with a given name, so we use
the name generated by kernel and rename the interface afterwards. A
race condition can happen during the rename: NM receives the interface
name from pppd, but in the meantime the interface could be deleted and
another one with that name could appear. In this case we would rename
the wrong interface.

Using a changing unit index, we ensure that interfaces created by NM
don't race with each others. There is still the chance to race with
externally-created interfaces, but I guess this is not easily solvable
since the pppd plugin does not expose the ifindex.

When the specified unit is already in use, the kernel selects another
one.

1 files changed, 10 insertions, 0 deletions

diff --git a/src/ppp/nm-ppp-manager.c b/src/ppp/nm-ppp-manager.c
index fec7ce375f..06703366f3 100644
--- a/src/ppp/nm-ppp-manager.c
+++ b/src/ppp/nm-ppp-manager.c
@@ -678,6 +678,7 @@ create_pppd_cmd_line (NMPPPManager *self,
 	const char *pppd_binary = NULL;
 	NMCmdLine *cmd;
 	gboolean ppp_debug;
+	static int unit;
 
 	g_return_val_if_fail (setting != NULL, NULL);
 
@@ -842,6 +843,15 @@ create_pppd_cmd_line (NMPPPManager *self,
 	nm_cmd_line_add_string (cmd, "plugin");
 	nm_cmd_line_add_string (cmd, NM_PPPD_PLUGIN);
 
+	if (pppoe && nm_setting_pppoe_get_parent (pppoe)) {
+		/* The PPP interface is going to be renamed, so pass a
+		 * different unit each time so that activations don't
+		 * race with each others. */
+		nm_cmd_line_add_string (cmd, "unit");
+		nm_cmd_line_add_int (cmd, unit);
+		unit = unit < G_MAXINT ? unit + 1 : 0;
+	}
+
 	return cmd;
 }