From: Johannes Berg <johannes.berg@intel.com>
Date: Wed, 28 Sep 2022 22:07:15 +0200
Subject: [PATCH 3/9] wifi: mac80211: fix MBSSID parsing use-after-free
Patch-mainline: Not yet, embargoed
References: CVE-2022-42719 bsc#1204051

When we parse a multi-BSSID element, we might point some
element pointers into the allocated nontransmitted_profile.
However, we free this before returning, causing UAF when the
relevant pointers in the parsed elements are accessed.

Fix this by not allocating the scratch buffer separately but
as part of the returned structure instead, that way, there
are no lifetime issues with it.

The scratch buffer introduction as part of the returned data
here is taken from MLO feature work done by Ilan.

This fixes CVE-2022-42719.

Fixes: 5023b14cf4df ("mac80211: support profile split between elements")
Co-developed-by: Ilan Peer <ilan.peer@intel.com>
Signed-off-by: Ilan Peer <ilan.peer@intel.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

---
 net/mac80211/ieee80211_i.h |    8 ++++++++
 net/mac80211/util.c        |   32 ++++++++++++++++----------------
 2 files changed, 24 insertions(+), 16 deletions(-)

--- a/net/mac80211/ieee80211_i.h
+++ b/net/mac80211/ieee80211_i.h
@@ -1601,6 +1601,14 @@ struct ieee802_11_elems {
 
 	/* whether a parse error occurred while retrieving these elements */
 	bool parse_error;
+
+	/*
+	 * scratch buffer that can be used for various element parsing related
+	 * tasks, e.g., element de-fragmentation etc.
+	 */
+	size_t scratch_len;
+	u8 *scratch_pos;
+	u8 scratch[];
 };
 
 static inline struct ieee80211_local *hw_to_local(
--- a/net/mac80211/util.c
+++ b/net/mac80211/util.c
@@ -1459,26 +1459,28 @@ ieee802_11_parse_elems_full(struct ieee8
 	const struct element *non_inherit = NULL;
 	u8 *nontransmitted_profile;
 	int nontransmitted_profile_len = 0;
+	size_t scratch_len = params->len;
 
-	elems = kzalloc(sizeof(*elems), GFP_ATOMIC);
+	elems = kzalloc(sizeof(*elems) + scratch_len, GFP_ATOMIC);
 	if (!elems)
 		return NULL;
 	elems->ie_start = params->start;
 	elems->total_len = params->len;
+	elems->scratch_len = scratch_len;
+	elems->scratch_pos = elems->scratch;
 
-	nontransmitted_profile = kmalloc(params->len, GFP_ATOMIC);
-	if (nontransmitted_profile) {
-		nontransmitted_profile_len =
-			ieee802_11_find_bssid_profile(params->start, params->len,
-						      elems,
-						      params->transmitter_bssid,
-						      params->bss_bssid,
-						      nontransmitted_profile);
-		non_inherit =
-			cfg80211_find_ext_elem(WLAN_EID_EXT_NON_INHERITANCE,
-					       nontransmitted_profile,
-					       nontransmitted_profile_len);
-	}
+	nontransmitted_profile = elems->scratch_pos;
+	nontransmitted_profile_len =
+		ieee802_11_find_bssid_profile(params->start, params->len,
+					      elems,
+					      params->transmitter_bssid,
+					      params->bss_bssid,
+					      nontransmitted_profile);
+	elems->scratch_pos += nontransmitted_profile_len;
+	elems->scratch_len -= nontransmitted_profile_len;
+	non_inherit = cfg80211_find_ext_elem(WLAN_EID_EXT_NON_INHERITANCE,
+					     nontransmitted_profile,
+					     nontransmitted_profile_len);
 
 	elems->crc = _ieee802_11_parse_elems_full(params, elems, non_inherit);
 
@@ -1511,8 +1513,6 @@ ieee802_11_parse_elems_full(struct ieee8
 	    offsetofend(struct ieee80211_bssid_index, dtim_count))
 		elems->dtim_count = elems->bssid_index->dtim_count;
 
-	kfree(nontransmitted_profile);
-
 	return elems;
 }