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From:   Luiz Augusto von Dentz <luiz.dentz@gmail.com>
Date:   Wed, 4 Jan 2023 14:21:29 -0800
Message-ID: <CABBYNZL9FiZjRYJE_h4n2kf9LKv_5XF3Fd=bz=cU4bTcDR-QHQ@mail.gmail.com>
Subject: Re: [PATCH v2] Bluetooth: Fix possible deadlock in rfcomm_sk_state_change
To:     Ying Hsu <yinghsu@chromium.org>
Cc:     linux-bluetooth@vger.kernel.org, marcel@holtmann.org,
        leon@kernel.org, chromeos-bluetooth-upstreaming@chromium.org,
        "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Johan Hedberg <johan.hedberg@gmail.com>,
        Paolo Abeni <pabeni@redhat.com>, linux-kernel@vger.kernel.org,
        netdev@vger.kernel.org
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Hi Ying,

On Wed, Jan 4, 2023 at 7:07 AM Ying Hsu <yinghsu@chromium.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@chromium.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
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