wifi: mac80211: fix multi-link element inheritance

When parsing a beacon, mac80211 erroneously inherits any
reconfiguration or EPCS multi-link elements from the outer
elements into the multi-BSSID profile that's requested, if
connected to a non-transmitted BSS, unless that profile
has a non-inheritance element.

This also happens if parsing a multi-BSSID profile that
doesn't have a non-inheritance element.

Fix this by having an empty non-inheritance element so
cfg80211_is_element_inherited() is invoked in these cases
and causes the parser to skip the elements that should
never be inherited.

Fixes: cf36cdef10e2 ("wifi: mac80211: Add support for parsing Reconfiguration Multi Link element")
Fixes: 24711d60f849 ("wifi: mac80211: Support parsing EPCS ML element")
Reviewed-by: Ilan Peer <ilan.peer@intel.com>
Reviewed-by: Benjamin Berg <benjamin.berg@intel.com>
Link: https://patch.msgid.link/20260508091032.92184c0a3f08.I3c43b0b63d2cef8a4ddddaef1c2faaeb1de711ad@changeid
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

1 files changed, 33 insertions, 3 deletions

diff --git a/net/mac80211/parse.c b/net/mac80211/parse.c
index 666cdd5fd0ea..77894d997113 100644
--- a/net/mac80211/parse.c
+++ b/net/mac80211/parse.c
@@ -34,6 +34,15 @@
 #include "led.h"
 #include "wep.h"
 
+static const u8 empty_non_inheritance[] = {
+	WLAN_EID_EXTENSION, 1, WLAN_EID_EXT_NON_INHERITANCE,
+	/*
+	 * cfg80211_is_element_inherited() hardcodes elements that
+	 * cannot be inherited, so we just need an empty one to be
+	 * calling it at all.
+	 */
+};
+
 struct ieee80211_elem_defrag {
 	const struct element *elem;
 	/* container start/len */
@@ -923,7 +932,7 @@ ieee80211_prep_mle_link_parse(struct ieee80211_elems_parse *elems_parse,
 {
 	struct ieee802_11_elems *elems = &elems_parse->elems;
 	struct ieee80211_mle_per_sta_profile *prof;
-	const struct element *tmp;
+	const struct element *tmp, *ret;
 	ssize_t ml_len;
 	const u8 *end;
 
@@ -993,8 +1002,17 @@ ieee80211_prep_mle_link_parse(struct ieee80211_elems_parse *elems_parse,
 	sub->from_ap = params->from_ap;
 	sub->link_id = -1;
 
-	return cfg80211_find_ext_elem(WLAN_EID_EXT_NON_INHERITANCE,
-				      sub->start, sub->len);
+	ret = cfg80211_find_ext_elem(WLAN_EID_EXT_NON_INHERITANCE,
+				     sub->start, sub->len);
+	if (ret)
+		return ret;
+
+	/*
+	 * Since we know we want and found a profile, apply an empty
+	 * non-inheritance if the profile didn't have one, so that any
+	 * element that shouldn't be inherited by spec isn't.
+	 */
+	return (const void *)empty_non_inheritance;
 }
 
 static const void *
@@ -1030,6 +1048,7 @@ ieee802_11_parse_elems_full(struct ieee80211_elems_parse_params *params)
 	size_t scratch_len = 3 * params->len;
 	bool multi_link_inner = false;
 
+	BUILD_BUG_ON(sizeof(empty_non_inheritance) != empty_non_inheritance[1] + 2);
 	BUILD_BUG_ON(offsetof(typeof(*elems_parse), elems) != 0);
 
 	/* cannot parse for both a specific link and non-transmitted BSS */
@@ -1077,6 +1096,17 @@ ieee802_11_parse_elems_full(struct ieee80211_elems_parse_params *params)
 
 		non_inherit = cfg80211_find_ext_elem(WLAN_EID_EXT_NON_INHERITANCE,
 						     sub.start, nontx_len);
+		/*
+		 * If it's a non-transmitted BSS, we shouldn't pick
+		 * any elements in the outer parsing that shouldn't
+		 * be inherited. If the profile has a non-inheritance
+		 * element this automatically happens, but if not then
+		 * provide an empty one so that the hard-coded elements
+		 * in cfg80211_is_element_inherited() are ignored, but
+		 * it must be called.
+		 */
+		if (params->bss->transmitted_bss && !non_inherit)
+			non_inherit = (const void *)empty_non_inheritance;
 	} else {
 		/* must always parse to get elems_parse->ml_basic_elem */
 		non_inherit = ieee80211_prep_mle_link_parse(elems_parse, params,