netdev - [PATCH 1/2] Bluetooth: call sock_hold earlier in sco_conn

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Date:   Thu,  2 Sep 2021 23:13:05 -0400
From:   Desmond Cheong Zhi Xi <desmondcheongzx@...il.com>
To:     marcel@...tmann.org, johan.hedberg@...il.com, luiz.dentz@...il.com,
        davem@...emloft.net, kuba@...nel.org
Cc:     Desmond Cheong Zhi Xi <desmondcheongzx@...il.com>,
        linux-bluetooth@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, eric.dumazet@...il.com
Subject: [PATCH 1/2] Bluetooth: call sock_hold earlier in sco_conn_del

In sco_conn_del, conn->sk is read while holding on to the
sco_conn.lock to avoid races with a socket that could be released
concurrently.

However, in between unlocking sco_conn.lock and calling sock_hold,
it's possible for the socket to be freed, which would cause a
use-after-free write when sock_hold is finally called.

To fix this, the reference count of the socket should be increased
while the sco_conn.lock is still held.

Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@...il.com>
---
 net/bluetooth/sco.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/bluetooth/sco.c b/net/bluetooth/sco.c
index b62c91c627e2..4a057f99b60a 100644
--- a/net/bluetooth/sco.c
+++ b/net/bluetooth/sco.c
@@ -187,10 +187,11 @@ static void sco_conn_del(struct hci_conn *hcon, int err)
 	/* Kill socket */
 	sco_conn_lock(conn);
 	sk = conn->sk;
+	if (sk)
+		sock_hold(sk);
 	sco_conn_unlock(conn);
 
 	if (sk) {
-		sock_hold(sk);
 		lock_sock(sk);
 		sco_sock_clear_timer(sk);
 		sco_chan_del(sk, err);
-- 
2.25.1