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From:   Siddh Raman Pant <code@siddh.me>
To:     Johannes Berg <johannes@sipsolutions.net>,
        "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>
Cc:     linux-wireless <linux-wireless@vger.kernel.org>,
        netdev <netdev@vger.kernel.org>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        linux-kernel-mentees 
        <linux-kernel-mentees@lists.linuxfoundation.org>,
        syzbot+f9acff9bf08a845f225d@syzkaller.appspotmail.com
Message-ID: <20220819200340.34826-1-code@siddh.me>
Subject: [PATCH v3] wifi: mac80211: Fix UAF in ieee80211_scan_rx()
Date:   Sat, 20 Aug 2022 01:33:40 +0530
MIME-Version: 1.0
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Precedence: bulk

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=3Df9acff9bf08a845f225d
Reported-by: syzbot+f9acff9bf08a845f225d@syzkaller.appspotmail.com
Suggested-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: Siddh Raman Pant <code@siddh.me>
---
Changes in v3:
Use Johannes Berg's suggestion as-it-is:
https://lore.kernel.org/netdev/18fd9b89d45aedc1504d0cbd299ffb289ae96438.cam=
el@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 ieee802=
11_hw *hw, bool aborted)
 =09scan_req =3D rcu_dereference_protected(local->scan_req,
 =09=09=09=09=09     lockdep_is_held(&local->mtx));
=20
-=09if (scan_req !=3D local->int_scan_req) {
-=09=09local->scan_info.aborted =3D aborted;
-=09=09cfg80211_scan_done(scan_req, &local->scan_info);
-=09}
 =09RCU_INIT_POINTER(local->scan_req, NULL);
 =09RCU_INIT_POINTER(local->scan_sdata, NULL);
=20
 =09local->scanning =3D 0;
 =09local->scan_chandef.chan =3D NULL;
=20
+=09synchronize_rcu();
+
+=09if (scan_req !=3D local->int_scan_req) {
+=09=09local->scan_info.aborted =3D aborted;
+=09=09cfg80211_scan_done(scan_req, &local->scan_info);
+=09}
+
 =09/* Set power back to normal operating levels. */
 =09ieee80211_hw_config(local, 0);
=20
--=20
2.35.1