[PATCH] mac80211: validate extended element ID is present

From: Johannes Berg <redacted>

Before attempting to parse an extended element, verify that
the extended element ID is present.

Fixes: 41cbb0f5a295 ("mac80211: add support for HE")
Reported-by: syzbot+59bdff68edce82e393b6@syzkaller.appspotmail.com
Signed-off-by: Johannes Berg <redacted>
---
 net/mac80211/util.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/net/mac80211/util.c b/net/mac80211/util.c
index 43df2f0c5db9..6c2934854d3c 100644
--- a/net/mac80211/util.c
+++ b/net/mac80211/util.c

@@ -943,7 +943,12 @@ static void ieee80211_parse_extension_element(u32 *crc,
 					      struct ieee802_11_elems *elems)
 {
 	const void *data = elem->data + 1;
-	u8 len = elem->datalen - 1;
+	u8 len;
+
+	if (!elem->datalen)
+		return;
+
+	len = elem->datalen - 1;
 
 	switch (elem->data[0]) {
 	case WLAN_EID_EXT_HE_MU_EDCA:

-- 
2.33.1