[PATCH 5.11 070/210] nl80211: fix beacon head validation

[Greg Kroah-Hartman]

From: Johannes Berg <johannes.berg@xxxxxxxxx>

commit 9a6847ba1747858ccac53c5aba3e25c54fbdf846 upstream.

If the beacon head attribute (NL80211_ATTR_BEACON_HEAD)
is too short to even contain the frame control field,
we access uninitialized data beyond the buffer. Fix this
by checking the minimal required size first. We used to
do this until S1G support was added, where the fixed
data portion has a different size.

Reported-and-tested-by: syzbot+72b99dcf4607e8c770f3@xxxxxxxxxxxxxxxxxxxxxxxxx
Suggested-by: Eric Dumazet <eric.dumazet@xxxxxxxxx>
Fixes: 1d47f1198d58 ("nl80211: correctly validate S1G beacon head")
Signed-off-by: Johannes Berg <johannes.berg@xxxxxxxxx>
Link: https://lore.kernel.org/r/20210408154518.d9b06d39b4ee.Iff908997b2a4067e8d456b3cb96cab9771d252b8@changeid
Signed-off-by: Johannes Berg <johannes.berg@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 net/wireless/nl80211.c |    6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

--- a/net/wireless/nl80211.c
+++ b/net/wireless/nl80211.c
@@ -209,9 +209,13 @@ static int validate_beacon_head(const st
 	unsigned int len = nla_len(attr);
 	const struct element *elem;
 	const struct ieee80211_mgmt *mgmt = (void *)data;
-	bool s1g_bcn = ieee80211_is_s1g_beacon(mgmt->frame_control);
 	unsigned int fixedlen, hdrlen;
+	bool s1g_bcn;
 
+	if (len < offsetofend(typeof(*mgmt), frame_control))
+		goto err;
+
+	s1g_bcn = ieee80211_is_s1g_beacon(mgmt->frame_control);
 	if (s1g_bcn) {
 		fixedlen = offsetof(struct ieee80211_ext,
 				    u.s1g_beacon.variable);