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From:   Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>
To:     marcel@holtmann.org, johan.hedberg@gmail.com, luiz.dentz@gmail.com,
        davem@davemloft.net, kuba@kernel.org, sudipm.mukherjee@gmail.com
Cc:     Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>,
        linux-bluetooth@vger.kernel.org, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org, skhan@linuxfoundation.org,
        gregkh@linuxfoundation.org,
        linux-kernel-mentees@lists.linuxfoundation.org
Subject: [PATCH v6 6/6] Bluetooth: fix repeated calls to sco_sock_kill
Date:   Tue, 10 Aug 2021 12:14:10 +0800
Message-Id: <20210810041410.142035-7-desmondcheongzx@gmail.com>
In-Reply-To: <20210810041410.142035-1-desmondcheongzx@gmail.com>
References: <20210810041410.142035-1-desmondcheongzx@gmail.com>
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Precedence: bulk

In commit 4e1a720d0312 ("Bluetooth: avoid killing an already killed
socket"), a check was added to sco_sock_kill to skip killing a socket
if the SOCK_DEAD flag was set.

This was done after a trace for a use-after-free bug showed that the
same sock pointer was being killed twice.

Unfortunately, this check prevents sco_sock_kill from running on any
socket. sco_sock_kill kills a socket only if it's zapped and orphaned,
however sock_orphan announces that the socket is dead before detaching
it. i.e., orphaned sockets have the SOCK_DEAD flag set.

To fix this, we remove the check for SOCK_DEAD, and avoid repeated
calls to sco_sock_kill by removing incorrect calls in:

1. sco_sock_timeout. The socket should not be killed on timeout as
further processing is expected to be done. For example,
sco_sock_connect sets the timer then waits for the socket to be
connected or for an error to be returned.

2. sco_conn_del. This function should clean up resources for the
connection, but the socket itself should be cleaned up in
sco_sock_release.

3. sco_sock_close. Calls to sco_sock_close in sco_sock_cleanup_listen
and sco_sock_release are followed by sco_sock_kill. Hence the
duplicated call should be removed.

Fixes: 4e1a720d0312 ("Bluetooth: avoid killing an already killed socket")
Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>
---
 net/bluetooth/sco.c | 7 +------
 1 file changed, 1 insertion(+), 6 deletions(-)

diff --git a/net/bluetooth/sco.c b/net/bluetooth/sco.c
index 77490338f4fa..98a881586512 100644
--- a/net/bluetooth/sco.c
+++ b/net/bluetooth/sco.c
@@ -97,8 +97,6 @@ static void sco_sock_timeout(struct work_struct *work)
 	sk->sk_err = ETIMEDOUT;
 	sk->sk_state_change(sk);
 	release_sock(sk);
-
-	sco_sock_kill(sk);
 	sock_put(sk);
 }
 
@@ -197,7 +195,6 @@ static void sco_conn_del(struct hci_conn *hcon, int err)
 		sco_sock_clear_timer(sk);
 		sco_chan_del(sk, err);
 		release_sock(sk);
-		sco_sock_kill(sk);
 		sock_put(sk);
 
 		/* Ensure no more work items will run before freeing conn. */
@@ -404,8 +401,7 @@ static void sco_sock_cleanup_listen(struct sock *parent)
  */
 static void sco_sock_kill(struct sock *sk)
 {
-	if (!sock_flag(sk, SOCK_ZAPPED) || sk->sk_socket ||
-	    sock_flag(sk, SOCK_DEAD))
+	if (!sock_flag(sk, SOCK_ZAPPED) || sk->sk_socket)
 		return;
 
 	BT_DBG("sk %p state %d", sk, sk->sk_state);
@@ -457,7 +453,6 @@ static void sco_sock_close(struct sock *sk)
 	sco_sock_clear_timer(sk);
 	__sco_sock_close(sk);
 	release_sock(sk);
-	sco_sock_kill(sk);
 }
 
 static void sco_skb_put_cmsg(struct sk_buff *skb, struct msghdr *msg,
-- 
2.25.1