[PATCH 5.4 54/71] mac80211: validate extended element ID is present

From: Johannes Berg <redacted>

commit 768c0b19b50665e337c96858aa2b7928d6dcf756 upstream.

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

Fixes: 41cbb0f5a295 ("mac80211: add support for HE")
Reported-by: <redacted>
Link: https://lore.kernel.org/r/20211211201023.f30a1b128c07.I5cacc176da94ba316877c6e10fe3ceec8b4dbd7d@changeid (local)
Cc: <redacted>
Signed-off-by: Johannes Berg <redacted>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 net/mac80211/util.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/net/mac80211/util.c
+++ b/net/mac80211/util.c

@@ -1227,6 +1227,8 @@ _ieee802_11_parse_elems_crc(const u8 *st
 				elems->max_idle_period_ie = (void *)pos;
 			break;
 		case WLAN_EID_EXTENSION:
+			if (!elen)
+				break;
 			if (pos[0] == WLAN_EID_EXT_HE_MU_EDCA &&
 			    elen >= (sizeof(*elems->mu_edca_param_set) + 1)) {
 				elems->mu_edca_param_set = (void *)&pos[1];