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From: Eric Dumazet <eric.dumazet@gmail.com>
To: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>,
	Eric Dumazet <eric.dumazet@gmail.com>,
	marcel@holtmann.org, johan.hedberg@gmail.com,
	luiz.dentz@gmail.com, davem@davemloft.net, kuba@kernel.org,
	sudipm.mukherjee@gmail.com
Cc: 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,
	syzbot+2f6d7c28bb4bf7e82060@syzkaller.appspotmail.com
Subject: Re: [PATCH v6 1/6] Bluetooth: schedule SCO timeouts with delayed_work
Date: Thu, 2 Sep 2021 14:41:21 -0700	[thread overview]
Message-ID: <94942257-927c-efbc-b3fd-44cc097ad71f@gmail.com> (raw)
In-Reply-To: <bad67d05-366b-bebe-cbdb-6555386497de@gmail.com>



On 9/2/21 12:32 PM, Desmond Cheong Zhi Xi wrote:
> 
> Hi Eric,
> 
> This actually seems to be a pre-existing error in sco_sock_connect that we now hit in sco_sock_timeout.
> 
> Any thoughts on the following patch to address the problem?
> 
> Link: https://lore.kernel.org/lkml/20210831065601.101185-1-desmondcheongzx@gmail.com/


syzbot is still working on finding a repro, this is obviously not trivial,
because this is a race window.

I think this can happen even with a single SCO connection.

This might be triggered more easily forcing a delay in sco_sock_timeout()

diff --git a/net/bluetooth/sco.c b/net/bluetooth/sco.c
index 98a88158651281c9f75c4e0371044251e976e7ef..71ebe0243fab106c676c308724fe3a3f92a62cbd 100644
--- a/net/bluetooth/sco.c
+++ b/net/bluetooth/sco.c
@@ -84,8 +84,14 @@ static void sco_sock_timeout(struct work_struct *work)
 
        sco_conn_lock(conn);
        sk = conn->sk;
-       if (sk)
+       if (sk) {
+               // lets pretend cpu has been busy (in interrupts) for 100ms
+               int i;
+               for (i=0;i<100000;i++)
+                       udelay(1);
+
                sock_hold(sk);
+       }
        sco_conn_unlock(conn);
 
        if (!sk)


Stack trace tells us that sco_sock_timeout() is running after last reference
on socket has been released.

__refcount_add include/linux/refcount.h:199 [inline]
 __refcount_inc include/linux/refcount.h:250 [inline]
 refcount_inc include/linux/refcount.h:267 [inline]
 sock_hold include/net/sock.h:702 [inline]
 sco_sock_timeout+0x216/0x290 net/bluetooth/sco.c:88
 process_one_work+0x98d/0x1630 kernel/workqueue.c:2276
 worker_thread+0x658/0x11f0 kernel/workqueue.c:2422
 kthread+0x3e5/0x4d0 kernel/kthread.c:319
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295

This is why I suggested to delay sock_put() to make sure this can not happen.

diff --git a/net/bluetooth/sco.c b/net/bluetooth/sco.c
index 98a88158651281c9f75c4e0371044251e976e7ef..bd0222e3f05a6bcb40cffe8405c9dfff98d7afde 100644
--- a/net/bluetooth/sco.c
+++ b/net/bluetooth/sco.c
@@ -195,10 +195,11 @@ static void sco_conn_del(struct hci_conn *hcon, int err)
                sco_sock_clear_timer(sk);
                sco_chan_del(sk, err);
                release_sock(sk);
-               sock_put(sk);
 
                /* Ensure no more work items will run before freeing conn. */
                cancel_delayed_work_sync(&conn->timeout_work);
+
+               sock_put(sk);
        }
 
        hcon->sco_data = NULL;

  reply	other threads:[~2021-09-02 21:41 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-10  4:14 [PATCH v6 0/6] Bluetooth: fix locking and socket killing in SCO and RFCOMM Desmond Cheong Zhi Xi
2021-08-10  4:14 ` [PATCH v6 1/6] Bluetooth: schedule SCO timeouts with delayed_work Desmond Cheong Zhi Xi
2021-09-02 19:17   ` Eric Dumazet
2021-09-02 19:32     ` Desmond Cheong Zhi Xi
2021-09-02 21:41       ` Eric Dumazet [this message]
2021-09-02 22:53         ` Desmond Cheong Zhi Xi
2021-09-02 23:05           ` Desmond Cheong Zhi Xi
2021-09-02 23:42             ` Luiz Augusto von Dentz
2021-09-03  3:17               ` Desmond Cheong Zhi Xi
2021-08-10  4:14 ` [PATCH v6 2/6] Bluetooth: avoid circular locks in sco_sock_connect Desmond Cheong Zhi Xi
2021-08-10  4:14 ` [PATCH v6 3/6] Bluetooth: switch to lock_sock in SCO Desmond Cheong Zhi Xi
2021-08-10  4:14 ` [PATCH v6 4/6] Bluetooth: serialize calls to sco_sock_{set,clear}_timer Desmond Cheong Zhi Xi
2021-08-10  4:14 ` [PATCH v6 5/6] Bluetooth: switch to lock_sock in RFCOMM Desmond Cheong Zhi Xi
2021-08-10  4:14 ` [PATCH v6 6/6] Bluetooth: fix repeated calls to sco_sock_kill Desmond Cheong Zhi Xi

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