[PATCH] P2P: Fix crash for failure case when WSC PIN is entered incorrectly.

Angie Chinchilla angie.v.chinchilla at intel.com
Tue Apr 3 17:55:48 EDT 2012


When forming a P2P group using WSC PIN method, if the pin is entered
incorrectly the P2P client supplicant instance will crash as a result
of cleanup happening on data that is still in use.

For example, here is the path for the first crash:
eap_wsc_process():
- creates struct wpabuf tmpbuf; on the stack
- sets data->in_buf = &tmpbuf;
- calls wps_process_msg()
- which calls wps_process_wsc_msg()
- which, in case WPS_M4: calls wps_fail_event()
- which calls wps->event_cb()
- wps->event_cb = wpa_supplicant_wps_event()
- wpa_supplicant_wps_event()
- wpa_supplicant_wps_event_fail()
- which calls wpas_clear_wps()
- which calls wpas_notify_network_removed()
- which calls wpas_p2p_network_removed()
- which calls wpas_p2p_group_formation_timeout()
- which calls wpas_group_formation_completed()
- which calls wpas_p2p_group_delete()
- which calls wpa_supplicant_remove_iface()
- which calls wpa_supplicant_deinit_iface()
- which calls wpa_supplicant_cleanup()
- which calls eapol_sm_deinit()
- ... which eventually uses the ptr data->in_buf to free tmpbuf, our
stack variable and then the supplicant crashes

If you fix this crash, you'll hit another. Fix it and then a segfault.
The way we're cleaning up and deleting data from under ourselves here
just isn't safe, so make the teardown portion of this async.

Signed-hostap: Angie Chinchilla <angie.v.chinchilla at intel.com>
Signed-hostap: Nirav Shah <nirav.j2.shah at intel.com>
intended-for: hostap-1
---
 wpa_supplicant/p2p_supplicant.c |   12 ++++++++++--
 1 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/wpa_supplicant/p2p_supplicant.c b/wpa_supplicant/p2p_supplicant.c
index 413d0b2..47a0994 100644
--- a/wpa_supplicant/p2p_supplicant.c
+++ b/wpa_supplicant/p2p_supplicant.c
@@ -4488,14 +4488,22 @@ int wpas_p2p_in_progress(struct wpa_supplicant *wpa_s)
 
 void wpas_p2p_network_removed(struct wpa_supplicant *wpa_s,
 			      struct wpa_ssid *ssid)
-
 {
 	if (wpa_s->p2p_in_provisioning && ssid->p2p_group &&
 	    eloop_cancel_timeout(wpas_p2p_group_formation_timeout,
 				 wpa_s->parent, NULL) > 0) {
+		/**
+		 * Remove the network by scheduling the group formation
+		 * timeout to happen immediately. The teardown code
+		 * needs to be scheduled to run asynch later so that we
+		 * don't delete data from under ourselves unexpectedly.
+		 * Calling wpas_p2p_group_formation_timeout directly
+		 * causes a series of crashes in WPS failure scenarios.
+		 */
 		wpa_printf(MSG_DEBUG, "P2P: Canceled group formation due to "
 			   "P2P group network getting removed");
-		wpas_p2p_group_formation_timeout(wpa_s->parent, NULL);
+		eloop_register_timeout(0, 0, wpas_p2p_group_formation_timeout,
+				       wpa_s->parent, NULL);
 	}
 }
 
-- 
1.7.0.4



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