[PATCH v2] wifi: mac80211: guard drv_net_setup_tc() against unbound AP_VLAN sdata

[PATCH v2] wifi: mac80211: guard drv_net_setup_tc() against unbound AP_VLAN sdata

[Ayushman Rout]

syzbot reports a NULL/invalid pointer dereference in
trace_event_raw_event_drv_net_setup_tc(), reached via
ieee80211_netdev_setup_tc() -> drv_net_setup_tc().

drv_net_setup_tc() calls get_bss_sdata(sdata) unconditionally. For an
NL80211_IFTYPE_AP_VLAN interface this does
container_of(sdata->bss, ...), but sdata->bss is only linked
opportunistically at interface-add time when a matching same-address
AP interface exists - it is not enforced, so an AP_VLAN interface can
be fully created and registered with sdata->bss left NULL.
container_of() on NULL yields a small invalid pointer rather than
NULL, which the trace_drv_net_setup_tc tracepoint then dereferences
to read the interface name.

Guard against an unbound AP_VLAN sdata before calling
get_bss_sdata(), matching the WARN_ON_ONCE(!bss) precondition already
used for this same relationship in sta_info.c.

The underlying gap in ieee80211_if_add() - AP_VLAN creation not
requiring a bound bss - is not fixed here; other get_bss_sdata()
callers may share the exposure.

Fixes: 61587f1556fe ("wifi: mac80211: add support for letting drivers register tc offload support")
Reported-by: syzbot+f1ba58d6b55abd13239e@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=f1ba58d6b55abd13239e
Signed-off-by: Ayushman Rout <ayushmanrout27@gmail.com>
---
v2: drop the check_sdata_in_driver() call from v1 - syzbot ci flagged
    it as reachable via ordinary tc qdisc creation, not a real bug.
    https://ci.syzbot.org/series/db0f7870-cfa6-4a9b-b78b-225ce86c2a89

 net/mac80211/driver-ops.h | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/net/mac80211/driver-ops.h b/net/mac80211/driver-ops.h
index f1c0b87fddd5..29743e19a61d 100644
--- a/net/mac80211/driver-ops.h
+++ b/net/mac80211/driver-ops.h
@@ -1702,6 +1702,15 @@ static inline int drv_net_setup_tc(struct ieee80211_local *local,
 
 	might_sleep();
 
+	/*
+	 * AP_VLAN interfaces are only linked to a bss opportunistically at
+	 * creation; an unbound one has sdata->bss == NULL, and
+	 * get_bss_sdata()'s container_of() on that yields a bogus pointer
+	 * rather than NULL, which the tracepoint below then dereferences.
+	 */
+	if (sdata->vif.type == NL80211_IFTYPE_AP_VLAN && !sdata->bss)
+		return -EIO;
+
 	sdata = get_bss_sdata(sdata);
 	trace_drv_net_setup_tc(local, sdata, type);
 	if (local->ops->net_setup_tc)
-- 
2.54.0