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From: Michal Kazior <michal.kazior@tieto.com>
To: linux-wireless@vger.kernel.org
Cc: johannes@sipsolutions.net, Michal Kazior <michal.kazior@tieto.com>
Subject: [PATCH v2 1/2] cfg80211: ignore netif running state when changing iftype
Date: Fri, 22 May 2015 10:57:22 +0200
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It was possible for mac80211 to be coerced into an
unexpected flow causing sdata union to become
corrupted. Station pointer was put into
sdata->u.vlan.sta memory location while it was
really master AP's sdata->u.ap.next_beacon. This
led to station entry being later freed as
next_beacon before __sta_info_flush() in
ieee80211_stop_ap() and a subsequent invalid
pointer dereference crash.

The problem was that ieee80211_ptr->use_4addr
wasn't cleared on interface type changes.

This could be reproduced with the following steps:

 # host A and host B have just booted; no
 # wpa_s/hostapd running; all vifs are down
 host A> iw wlan0 set type station
 host A> iw wlan0 set 4addr on
 host A> printf 'interface=wlan0\nssid=4addrcrash\nchannel=1\nwds_sta=1' > /tmp/hconf
 host A> hostapd -B /tmp/conf
 host B> iw wlan0 set 4addr on
 host B> ifconfig wlan0 up
 host B> iw wlan0 connect -w hostAssid
 host A> pkill hostapd
 # host A crashed:

 [  127.928192] BUG: unable to handle kernel NULL pointer dereference at 00000000000006c8
 [  127.929014] IP: [<ffffffff816f4f32>] __sta_info_flush+0xac/0x158
 ...
 [  127.934578]  [<ffffffff8170789e>] ieee80211_stop_ap+0x139/0x26c
 [  127.934578]  [<ffffffff8100498f>] ? dump_trace+0x279/0x28a
 [  127.934578]  [<ffffffff816dc661>] __cfg80211_stop_ap+0x84/0x191
 [  127.934578]  [<ffffffff816dc7ad>] cfg80211_stop_ap+0x3f/0x58
 [  127.934578]  [<ffffffff816c5ad6>] nl80211_stop_ap+0x1b/0x1d
 [  127.934578]  [<ffffffff815e53f8>] genl_family_rcv_msg+0x259/0x2b5

Note: This isn't a revert of f8cdddb8d61d
("cfg80211: check iface combinations only when
iface is running") as far as functionality is
considered because b6a550156bc ("cfg80211/mac80211:
move more combination checks to mac80211") moved
the logic somewhere else already.

Fixes: f8cdddb8d61d ("cfg80211: check iface combinations only when iface is running")
Signed-off-by: Michal Kazior <michal.kazior@tieto.com>
---

Notes:
    v2:
     * improve commit log [Johannes]

 net/wireless/util.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/wireless/util.c b/net/wireless/util.c
index 70051ab52f4f..7e4e3fffe7ce 100644
--- a/net/wireless/util.c
+++ b/net/wireless/util.c
@@ -944,7 +944,7 @@ int cfg80211_change_iface(struct cfg80211_registered_device *rdev,
 	     ntype == NL80211_IFTYPE_P2P_CLIENT))
 		return -EBUSY;
 
-	if (ntype != otype && netif_running(dev)) {
+	if (ntype != otype) {
 		dev->ieee80211_ptr->use_4addr = false;
 		dev->ieee80211_ptr->mesh_id_up_len = 0;
 		wdev_lock(dev->ieee80211_ptr);
-- 
2.1.4