On Fri, 2015-05-22 at 10:57 +0200, Michal Kazior wrote: > 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 > > Even though this can and should be fixed in > cfg80211 it still makes sense to add a sanity > check to mac80211 to prevent future problems. I'm a bit undecided about this. Is this really the only place that assumes use_4addr implies that it's a VLAN, in a context like this? johannes -- To unsubscribe from this list: send the line "unsubscribe linux-wireless" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
