Date:   Thu, 5 Jan 2023 17:18:33 -0800
From:   Saeed Mahameed <saeed@...nel.org>
To:     Luiz Augusto von Dentz <luiz.dentz@...il.com>
Cc:     Ying Hsu <yinghsu@...omium.org>, linux-bluetooth@...r.kernel.org,
        marcel@...tmann.org, leon@...nel.org,
        chromeos-bluetooth-upstreaming@...omium.org,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Johan Hedberg <johan.hedberg@...il.com>,
        Paolo Abeni <pabeni@...hat.com>, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org
Subject: Re: [PATCH v2] Bluetooth: Fix possible deadlock in
 rfcomm_sk_state_change

On 04 Jan 14:21, Luiz Augusto von Dentz wrote:
>Hi Ying,
>
>On Wed, Jan 4, 2023 at 7:07 AM Ying Hsu <yinghsu@...omium.org> wrote:
>>
>> There's a possible deadlock when two processes are connecting
>> and closing a RFCOMM socket concurrently. Here's the call trace:
>
>Are you sure it is 2 different processes? Usually that would mean 2
>different sockets (sk) then so they wouldn't share the same lock, so
>this sounds more like 2 different threads, perhaps it is worth
>creating a testing case in our rfcomm-tester so we are able to detect
>this sort of thing in the future.
>
>> -> #2 (&d->lock){+.+.}-{3:3}:
>>        __mutex_lock_common kernel/locking/mutex.c:603 [inline]
>>        __mutex_lock0x12f/0x1360 kernel/locking/mutex.c:747
>>        __rfcomm_dlc_close+0x15d/0x890 net/bluetooth/rfcomm/core.c:487
>>        rfcomm_dlc_close+1e9/0x240 net/bluetooth/rfcomm/core.c:520
>>        __rfcomm_sock_close+0x13c/0x250 net/bluetooth/rfcomm/sock.c:220
>>        rfcomm_sock_shutdown+0xd8/0x230 net/bluetooth/rfcomm/sock.c:907
>>        rfcomm_sock_release+0x68/0x140 net/bluetooth/rfcomm/sock.c:928
>>        __sock_release+0xcd/0x280 net/socket.c:650
>>        sock_close+0x1c/0x20 net/socket.c:1365
>>        __fput+0x27c/0xa90 fs/file_table.c:320
>>        task_work_run+0x16f/0x270 kernel/task_work.c:179
>>        exit_task_work include/linux/task_work.h:38 [inline]
>>        do_exit+0xaa8/0x2950 kernel/exit.c:867
>>        do_group_exit+0xd4/0x2a0 kernel/exit.c:1012
>>        get_signal+0x21c3/0x2450 kernel/signal.c:2859
>>        arch_do_signal_or_restart+0x79/0x5c0 arch/x86/kernel/signal.c:306
>>        exit_to_user_mode_loop kernel/entry/common.c:168 [inline]
>>        exit_to_user_mode_prepare+0x15f/0x250 kernel/entry/common.c:203
>>        __syscall_exit_to_user_mode_work kernel/entry/common.c:285 [inline]
>>        syscall_exit_to_user_mode+0x1d/0x50 kernel/entry/common.c:296
>>        do_syscall_64+0x46/0xb0 arch/x86/entry/common.c:86
>>        entry_SYSCALL_64_after_hwframe+0x63/0xcd
>>
>> -> #1 (rfcomm_mutex){+.+.}-{3:3}:
>>        __mutex_lock_common kernel/locking/mutex.c:603 [inline]
>>        __mutex_lock+0x12f/0x1360 kernel/locking/mutex.c:747
>>        rfcomm_dlc_open+0x93/0xa80 net/bluetooth/rfcomm/core.c:425
>>        rfcomm_sock_connect+0x329/0x450 net/bluetooth/rfcomm/sock.c:413
>>        __sys_connect_file+0x153/0x1a0 net/socket.c:1976
>>        __sys_connect+0x165/0x1a0 net/socket.c:1993
>>        __do_sys_connect net/socket.c:2003 [inline]
>>        __se_sys_connect net/socket.c:2000 [inline]
>>        __x64_sys_connect+0x73/0xb0 net/socket.c:2000
>>        do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>>        do_syscall_64+0x39/0xb0 arch/x86/entry/common.c:80
>>        entry_SYSCALL_64_after_hwframe+0x63/0xcd
>>
>> -> #0 (sk_lock-AF_BLUETOOTH-BTPROTO_RFCOMM){+.+.}-{0:0}:
>>        check_prev_add kernel/locking/lockdep.c:3097 [inline]
>>        check_prevs_add kernel/locking/lockdep.c:3216 [inline]
>>        validate_chain kernel/locking/lockdep.c:3831 [inline]
>>        __lock_acquire+0x2a43/0x56d0 kernel/locking/lockdep.c:5055
>>        lock_acquire kernel/locking/lockdep.c:5668 [inline]
>>        lock_acquire+0x1e3/0x630 kernel/locking/lockdep.c:5633
>>        lock_sock_nested+0x3a/0xf0 net/core/sock.c:3470
>>        lock_sock include/net/sock.h:1725 [inline]
>>        rfcomm_sk_state_change+0x6d/0x3a0 net/bluetooth/rfcomm/sock.c:73
>>        __rfcomm_dlc_close+0x1b1/0x890 net/bluetooth/rfcomm/core.c:489
>>        rfcomm_dlc_close+0x1e9/0x240 net/bluetooth/rfcomm/core.c:520
>>        __rfcomm_sock_close+0x13c/0x250 net/bluetooth/rfcomm/sock.c:220
>>        rfcomm_sock_shutdown+0xd8/0x230 net/bluetooth/rfcomm/sock.c:907
>>        rfcomm_sock_release+0x68/0x140 net/bluetooth/rfcomm/sock.c:928
>>        __sock_release+0xcd/0x280 net/socket.c:650
>>        sock_close+0x1c/0x20 net/socket.c:1365
>>        __fput+0x27c/0xa90 fs/file_table.c:320
>>        task_work_run+0x16f/0x270 kernel/task_work.c:179
>>        exit_task_work include/linux/task_work.h:38 [inline]
>>        do_exit+0xaa8/0x2950 kernel/exit.c:867
>>        do_group_exit+0xd4/0x2a0 kernel/exit.c:1012
>>        get_signal+0x21c3/0x2450 kernel/signal.c:2859
>>        arch_do_signal_or_restart+0x79/0x5c0 arch/x86/kernel/signal.c:306
>>        exit_to_user_mode_loop kernel/entry/common.c:168 [inline]
>>        exit_to_user_mode_prepare+0x15f/0x250 kernel/entry/common.c:203
>>        __syscall_exit_to_user_mode_work kernel/entry/common.c:285 [inline]
>>        syscall_exit_to_user_mode+0x1d/0x50 kernel/entry/common.c:296
>>        do_syscall_64+0x46/0xb0 arch/x86/entry/common.c:86
>>        entry_SYSCALL_64_after_hwframe+0x63/0xcd
>>
>> Signed-off-by: Ying Hsu <yinghsu@...omium.org>
>> ---
>> This commit has been tested with a C reproducer on qemu-x86_64
>> and a ChromeOS device.
>>
>> Changes in v2:
>> - Fix potential use-after-free in rfc_comm_sock_connect.
>>
>>  net/bluetooth/rfcomm/sock.c | 7 ++++++-
>>  1 file changed, 6 insertions(+), 1 deletion(-)
>>
>> diff --git a/net/bluetooth/rfcomm/sock.c b/net/bluetooth/rfcomm/sock.c
>> index 21e24da4847f..4397e14ff560 100644
>> --- a/net/bluetooth/rfcomm/sock.c
>> +++ b/net/bluetooth/rfcomm/sock.c
>> @@ -391,6 +391,7 @@ static int rfcomm_sock_connect(struct socket *sock, struct sockaddr *addr, int a
>>             addr->sa_family != AF_BLUETOOTH)
>>                 return -EINVAL;
>>
>> +       sock_hold(sk);
>>         lock_sock(sk);
>>
>>         if (sk->sk_state != BT_OPEN && sk->sk_state != BT_BOUND) {
>> @@ -410,14 +411,18 @@ static int rfcomm_sock_connect(struct socket *sock, struct sockaddr *addr, int a
>>         d->sec_level = rfcomm_pi(sk)->sec_level;
>>         d->role_switch = rfcomm_pi(sk)->role_switch;
>>
>> +       /* Drop sock lock to avoid potential deadlock with the RFCOMM lock */
>> +       release_sock(sk);
>>         err = rfcomm_dlc_open(d, &rfcomm_pi(sk)->src, &sa->rc_bdaddr,
>>                               sa->rc_channel);
>> -       if (!err)
>> +       lock_sock(sk);
>> +       if (!err && !sock_flag(sk, SOCK_ZAPPED))
>>                 err = bt_sock_wait_state(sk, BT_CONNECTED,
>>                                 sock_sndtimeo(sk, flags & O_NONBLOCK));
>>
>>  done:
>>         release_sock(sk);
>> +       sock_put(sk);
>>         return err;
>>  }
>
>This sounds like a great solution to hold the reference and then

Why do you need sock_hold/put in the same proto_ops.callback sock opts ? 
it should be guaranteed by the caller the sk will remain valid 
or if you are paranoid then sock_hold() on your proto_ops.bind() and put()
on your proto_ops.release()

>checking if the socket has been zapped when attempting to lock_sock,
>so Ive been thinking on generalize this into something like
>bt_sock_connect(sock, addr, alen, callback) so we make sure the
>callback is done while holding a reference but with the socket
>unlocked since typically the underline procedure only needs to access
>the pi(sk) information without changing it e.g. rfcomm_dlc_open,
>anyway Im fine if you don't want to pursue doing it right now but I'm
>afraid these type of locking problem is no restricted to RFCOMM only.
>
>> --
>> 2.39.0.314.g84b9a713c41-goog
>>
>
>
>-- 
>Luiz Augusto von Dentz

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