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Date:   Wed, 21 Jul 2021 20:26:20 +0200 (CEST)
From:   Jiri Kosina <jikos@kernel.org>
To:     Lin Ma <linma@zju.edu.cn>, Marcel Holtmann <marcel@holtmann.org>,
        Johan Hedberg <johan.hedberg@gmail.com>,
        Luiz Augusto von Dentz <luiz.dentz@gmail.com>
cc:     linux-bluetooth@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: Two issues caused by commit e305509e678b3 ("Bluetooth: use
 correct lock to prevent UAF of hdev object")
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References: <nycvar.YFH.7.76.2107131924280.8253@cbobk.fhfr.pm>
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On Tue, 13 Jul 2021, Jiri Kosina wrote:

> Hi,
> 
> commit e305509e678b3 ("Bluetooth: use correct lock to prevent UAF of hdev 
> object") has two issues, and I believe it should be reverted for 5.14 
> final. Could you please elaborate what is the exact UAF scenario the patch 
> is fixing? It's rather hard to deduce from the very short changelog, but 
> it's pretty obvious that it creates at least two issues.

Marcel, Johan, Luiz, any thoughts on this please? Thanks.

> 
> 
> 
> (1) it introduces a possibility of deadlock between hci_sock_dev_event() 
>    and hci_sock_sendmsg().
> 
> Namely:
> 
> - hci_sock_sendmsg(HCI_CHANNEL_LOGGING) acquires lock_sock(sk) and then 
>   calls into hci_logging_frame() -> hci_send_to_channel() which in turn 
>   acquires hci_sk_list.lock
> 
> - after the mentioned commit, hci_sock_dev_event() first acquires 
>   hci_sk_list.lock before doing lock_sock(sk) on each of the sockets it
>   iterates through, creating the reverse dependency
> 
> 
> Please find the full lockdep report below for reference.
> 
> (2) it causes sleeping function to be called from atomic context, because 
>    it's not allowed to sleep after acquiring read_lock(), which is exactly 
>    what this patch does (lock_sock() is sleepable). Report below as well.
> 
> 
> 
> 
> 
> 
>  BUG: sleeping function called from invalid context at net/core/sock.c:3100
>  in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 448, name: kworker/0:5
>  6 locks held by kworker/0:5/448:
>   #0: ffff89e947fb4338 ((wq_completion)usb_hub_wq){+.+.}-{0:0}, at: process_one_work+0x1c2/0x5e0
>   #1: ffffadef40973e78 ((work_completion)(&hub->events)){+.+.}-{0:0}, at: process_one_work+0x1c2/0x5e0
>   #2: ffff89e946998a20 (&dev->mutex){....}-{3:3}, at: hub_event+0x6a/0xd50 [usbcore]
>   #3: ffff89e950828a20 (&dev->mutex){....}-{3:3}, at: usb_disconnect+0x54/0x270 [usbcore]
>   #4: ffff89e9504e71a8 (&dev->mutex){....}-{3:3}, at: device_release_driver_internal+0x1a/0x1d0
>   #5: ffffffffc117a3c0 (hci_sk_list.lock){++++}-{2:2}, at: hci_sock_dev_event+0x12b/0x1e0 [bluetooth]
>  CPU: 0 PID: 448 Comm: kworker/0:5 Not tainted 5.14.0-rc1-00003-g7fef2edf7cc7 #15
>  Hardware name: LENOVO 20K5S22R00/20K5S22R00, BIOS R0IET38W (1.16 ) 05/31/2017
>  Workqueue: usb_hub_wq hub_event [usbcore]
>  Call Trace:
>   dump_stack_lvl+0x56/0x6c
>   ___might_sleep+0x1b6/0x210
>   lock_sock_nested+0x29/0xa0
>   hci_sock_dev_event+0x156/0x1e0 [bluetooth]
>   hci_unregister_dev+0xd2/0x350 [bluetooth]
>   btusb_disconnect+0x63/0x150 [btusb]
>   usb_unbind_interface+0x79/0x260 [usbcore]
>   device_release_driver_internal+0xf7/0x1d0
>   bus_remove_device+0xef/0x160
>   device_del+0x1ac/0x430
>   ? usb_remove_ep_devs+0x1b/0x30 [usbcore]
>   usb_disable_device+0x8d/0x1a0 [usbcore]
>   usb_disconnect+0xc1/0x270 [usbcore]
>   ? hub_event+0x4b0/0xd50 [usbcore]
>   hub_port_connect+0x82/0xa20 [usbcore]
>   ? __mutex_unlock_slowpath+0x43/0x2b0
>   hub_event+0x4c4/0xd50 [usbcore]
>   ? lock_is_held_type+0xb4/0x120
>   process_one_work+0x244/0x5e0
>   worker_thread+0x3c/0x390
>   ? process_one_work+0x5e0/0x5e0
>   kthread+0x133/0x160
>   ? set_kthread_struct+0x40/0x40
>   ret_from_fork+0x22/0x30
> 
>  ======================================================
>  WARNING: possible circular locking dependency detected
>  5.14.0-rc1-00003-g7fef2edf7cc7 #15 Tainted: G        W        
>  ------------------------------------------------------
>  kworker/0:5/448 is trying to acquire lock:
>  ffff89e950647920 (sk_lock-AF_BLUETOOTH-BTPROTO_HCI){+.+.}-{0:0}, at: hci_sock_dev_event+0x156/0x1e0 [bluetooth]
>  
>  but task is already holding lock:
>  ffffffffc117a3c0 (hci_sk_list.lock){++++}-{2:2}, at: hci_sock_dev_event+0x12b/0x1e0 [bluetooth]
>  
>  which lock already depends on the new lock.
> 
>  
>  the existing dependency chain (in reverse order) is:
>  
>  -> #1 (hci_sk_list.lock){++++}-{2:2}:
>         _raw_read_lock+0x38/0x70
>  systemd-sysv-generator[1254]: stat() failed on /etc/init.d/jexec, ignoring: No such file or directory
>         hci_send_to_channel+0x22/0x50 [bluetooth]
>         hci_sock_sendmsg+0xa2b/0xa40 [bluetooth]
>         sock_sendmsg+0x5b/0x60
>         ____sys_sendmsg+0x1ed/0x250
>  systemd-sysv-generator[1254]: SysV service '/etc/init.d/tpfand' lacks a native systemd unit file. Automatically generating a unit file for compatibility. Please update package to include a native systemd unit file, in order to make it more safe and robust.
>         ___sys_sendmsg+0x88/0xd0
>         __sys_sendmsg+0x5e/0xa0
>         do_syscall_64+0x3a/0xb0
>  systemd-sysv-generator[1254]: SysV service '/etc/init.d/boot.local' lacks a native systemd unit file. Automatically generating a unit file for compatibility. Please update package to include a native systemd unit file, in order to make it more safe and robust.
>         entry_SYSCALL_64_after_hwframe+0x44/0xae
>  
>  -> #0 (sk_lock-AF_BLUETOOTH-BTPROTO_HCI){+.+.}-{0:0}:
>         __lock_acquire+0x124a/0x1680
>         lock_acquire+0x278/0x300
>         lock_sock_nested+0x72/0xa0
>         hci_sock_dev_event+0x156/0x1e0 [bluetooth]
>         hci_unregister_dev+0xd2/0x350 [bluetooth]
>         btusb_disconnect+0x63/0x150 [btusb]
>         usb_unbind_interface+0x79/0x260 [usbcore]
>         device_release_driver_internal+0xf7/0x1d0
>         bus_remove_device+0xef/0x160
>         device_del+0x1ac/0x430
>         usb_disable_device+0x8d/0x1a0 [usbcore]
>         usb_disconnect+0xc1/0x270 [usbcore]
>         hub_port_connect+0x82/0xa20 [usbcore]
>         hub_event+0x4c4/0xd50 [usbcore]
>         process_one_work+0x244/0x5e0
>         worker_thread+0x3c/0x390
>         kthread+0x133/0x160
>         ret_from_fork+0x22/0x30
>  
>  other info that might help us debug this:
> 
>   Possible unsafe locking scenario:
> 
>         CPU0                    CPU1
>         ----                    ----
>    lock(hci_sk_list.lock);
>                                 lock(sk_lock-AF_BLUETOOTH-BTPROTO_HCI);
>                                 lock(hci_sk_list.lock);
>    lock(sk_lock-AF_BLUETOOTH-BTPROTO_HCI);
>  
>   *** DEADLOCK ***
> 
>  6 locks held by kworker/0:5/448:
>   #0: ffff89e947fb4338 ((wq_completion)usb_hub_wq){+.+.}-{0:0}, at: process_one_work+0x1c2/0x5e0
>   #1: ffffadef40973e78 ((work_completion)(&hub->events)){+.+.}-{0:0}, at: process_one_work+0x1c2/0x5e0
>   #2: ffff89e946998a20 (&dev->mutex){....}-{3:3}, at: hub_event+0x6a/0xd50 [usbcore]
>   #3: ffff89e950828a20 (&dev->mutex){....}-{3:3}, at: usb_disconnect+0x54/0x270 [usbcore]
>   #4: ffff89e9504e71a8 (&dev->mutex){....}-{3:3}, at: device_release_driver_internal+0x1a/0x1d0
>   #5: ffffffffc117a3c0 (hci_sk_list.lock){++++}-{2:2}, at: hci_sock_dev_event+0x12b/0x1e0 [bluetooth]
>  
>  stack backtrace:
>  CPU: 0 PID: 448 Comm: kworker/0:5 Tainted: G        W         5.14.0-rc1-00003-g7fef2edf7cc7 #15
>  Hardware name: LENOVO 20K5S22R00/20K5S22R00, BIOS R0IET38W (1.16 ) 05/31/2017
>  Workqueue: usb_hub_wq hub_event [usbcore]
>  Call Trace:
>   dump_stack_lvl+0x56/0x6c
>   check_noncircular+0x105/0x120
>   ? stack_trace_save+0x4b/0x70
>   ? save_trace+0x3d/0x340
>   ? __lock_acquire+0x124a/0x1680
>   __lock_acquire+0x124a/0x1680
>   lock_acquire+0x278/0x300
>   ? hci_sock_dev_event+0x156/0x1e0 [bluetooth]
>   ? lock_release+0x15a/0x2a0
>   lock_sock_nested+0x72/0xa0
>   ? hci_sock_dev_event+0x156/0x1e0 [bluetooth]
>   hci_sock_dev_event+0x156/0x1e0 [bluetooth]
>   hci_unregister_dev+0xd2/0x350 [bluetooth]
>   btusb_disconnect+0x63/0x150 [btusb]
>   usb_unbind_interface+0x79/0x260 [usbcore]
>   device_release_driver_internal+0xf7/0x1d0
>   bus_remove_device+0xef/0x160
>   device_del+0x1ac/0x430
>   ? usb_remove_ep_devs+0x1b/0x30 [usbcore]
>   usb_disable_device+0x8d/0x1a0 [usbcore]
>   usb_disconnect+0xc1/0x270 [usbcore]
>   ? hub_event+0x4b0/0xd50 [usbcore]
>   hub_port_connect+0x82/0xa20 [usbcore]
>   ? __mutex_unlock_slowpath+0x43/0x2b0
>   hub_event+0x4c4/0xd50 [usbcore]
>   ? lock_is_held_type+0xb4/0x120
>   process_one_work+0x244/0x5e0
>   worker_thread+0x3c/0x390
>   ? process_one_work+0x5e0/0x5e0
>   kthread+0x133/0x160
>   ? set_kthread_struct+0x40/0x40
>   ret_from_fork+0x22/0x30
> 
> 
> 
> -- 
> Jiri Kosina
> SUSE Labs
> 

-- 
Jiri Kosina
SUSE Labs