[PATCH] hostapd: Fix segfault after ACS when flushing STAs

Helmut Schaa helmut.schaa at googlemail.com
Thu Oct 10 03:48:56 EDT 2013

When hostapd receives an auth frame during ACS the transmission of
the according auth response will always fail:

ACS: Automatic channel selection started, this may take a bit
send_auth_reply: send: Resource temporarily unavailable

However, a station info entry was created. Once ACS is finished
it will flush all stations even though hapd was not yet fully
initialized. This results in a segfault when trying to access

0  0x0042c1c0 in radius_client_flush_auth ()
1  0x00416a94 in ap_free_sta ()
2  0x00416cc0 in hostapd_free_stas ()
3  0x0040bce8 in hostapd_flush_old_stations ()
4  0x0040c790 in hostapd_setup_interface_complete ()
5  0x0046347c in acs_scan_complete ()
6  0x0040f834 in hostapd_wpa_event ()
7  0x0043af08 in send_scan_event.part.46 ()
8  0x00443a64 in send_scan_event ()
9  0x00443c24 in do_process_drv_event ()
10 0x004449e8 in process_global_event ()
11 0x7767d7d0 in ?? ()

Fix this by not presuming anything about the initialization state of
hapd and checking ->radius before accessing.

Signed-off-hostapd: Helmut Schaa <helmut.schaa at googlemail.com>

Actually, this is more a workaround then a proper fix since I think
hostapd should not accept any mgmt frames during ACS and as such the
STA list should always be empty.  However, accessing anything outside
the scope of a single sta_info from ap_free_sta should be protected by
a NULL check.

 src/ap/sta_info.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/ap/sta_info.c b/src/ap/sta_info.c
index 6704c09..016b9b6 100644
--- a/src/ap/sta_info.c
+++ b/src/ap/sta_info.c
@@ -232,7 +232,8 @@ void ap_free_sta(struct hostapd_data *hapd, struct sta_info *sta)
 	rsn_preauth_free_station(hapd, sta);
-	radius_client_flush_auth(hapd->radius, sta->addr);
+	if (hapd->radius)
+		radius_client_flush_auth(hapd->radius, sta->addr);
 #endif /* CONFIG_NO_RADIUS */

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