netdev - [PATCH v3] wifi: mac80211: Fix UAF in ieee80211_scan

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Message-ID: <20220819200340.34826-1-code@siddh.me>
Date:   Sat, 20 Aug 2022 01:33:40 +0530
From:   Siddh Raman Pant <code@...dh.me>
To:     Johannes Berg <johannes@...solutions.net>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>
Cc:     linux-wireless <linux-wireless@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-kernel-mentees 
        <linux-kernel-mentees@...ts.linuxfoundation.org>,
        syzbot+f9acff9bf08a845f225d@...kaller.appspotmail.com
Subject: [PATCH v3] wifi: mac80211: Fix UAF in ieee80211_scan_rx()

ieee80211_scan_rx() tries to access scan_req->flags after a
null check, but a UAF is observed when the scan is completed
and __ieee80211_scan_completed() executes, which then calls
cfg80211_scan_done() leading to the freeing of scan_req.

Since scan_req is rcu_dereference()'d, prevent the racing in
__ieee80211_scan_completed() by ensuring that from mac80211's
POV it is no longer accessed from an RCU read critical section
before we call cfg80211_scan_done().

Bug report: https://syzkaller.appspot.com/bug?extid=f9acff9bf08a845f225d
Reported-by: syzbot+f9acff9bf08a845f225d@...kaller.appspotmail.com
Suggested-by: Johannes Berg <johannes@...solutions.net>
Signed-off-by: Siddh Raman Pant <code@...dh.me>
---
Changes in v3:
Use Johannes Berg's suggestion as-it-is:
https://lore.kernel.org/netdev/18fd9b89d45aedc1504d0cbd299ffb289ae96438.camel@sipsolutions.net/

v2 is now obsolete since it was an incorrect way to go about things.

 net/mac80211/scan.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/net/mac80211/scan.c b/net/mac80211/scan.c
index fa8ddf576bc1..c4f2aeb31da3 100644
--- a/net/mac80211/scan.c
+++ b/net/mac80211/scan.c
@@ -469,16 +469,19 @@ static void __ieee80211_scan_completed(struct ieee80211_hw *hw, bool aborted)
 	scan_req = rcu_dereference_protected(local->scan_req,
 					     lockdep_is_held(&local->mtx));
 
-	if (scan_req != local->int_scan_req) {
-		local->scan_info.aborted = aborted;
-		cfg80211_scan_done(scan_req, &local->scan_info);
-	}
 	RCU_INIT_POINTER(local->scan_req, NULL);
 	RCU_INIT_POINTER(local->scan_sdata, NULL);
 
 	local->scanning = 0;
 	local->scan_chandef.chan = NULL;
 
+	synchronize_rcu();
+
+	if (scan_req != local->int_scan_req) {
+		local->scan_info.aborted = aborted;
+		cfg80211_scan_done(scan_req, &local->scan_info);
+	}
+
 	/* Set power back to normal operating levels. */
 	ieee80211_hw_config(local, 0);
 
-- 
2.35.1