[PATCH] Bluetooth: hci_core: fix potential deadlock on &hci_dev_list_lock

[PATCH] Bluetooth: hci_core: fix potential deadlock on &hci_dev_list_lock

[Chengfeng Ye]

&hci_dev_list_lock is acquired under a2mp_chan_recv_cb(), which I
think should be a softirq context cb. So it seems that the
write_lock() on &hci_dev_list_lock should at least disable bh.
hci_register_dev() and hci_unregister_dev() are exactly that two
functions acquire &hci_dev_list_lock with write_lock(), and should
be called under process context without disable bh at most case.

Note that I am not sure whether this could happen at real, as I
am not sure whether the rx callback could be invoked during
register() and unregister().

<deadlock #1>
hci_register_dev()
--> write_lock(&hci_dev_list_lock)
<interrupt>
   --> a2mp_chan_recv_cb()
   --> a2mp_discover_req()
   --> read_lock(&hci_dev_list_lock)

<deadlock #2>
hci_unregister_dev()
--> write_lock(&hci_dev_list_lock)
<interrupt>
   --> a2mp_chan_recv_cb()
   --> a2mp_discover_req()
   --> read_lock(&hci_dev_list_lock)

This flaw was found by an experimental static analysis tool I am
developing for irq-related deadlock.

To prevent the potential problem, I change to write_lock_bh().

Signed-off-by: Chengfeng Ye <dg573847474@gmail.com>
---
 net/bluetooth/hci_core.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/net/bluetooth/hci_core.c b/net/bluetooth/hci_core.c
index a5992f1b3c9b..dd3107daed03 100644
--- a/net/bluetooth/hci_core.c
+++ b/net/bluetooth/hci_core.c
@@ -2670,9 +2670,9 @@ int hci_register_dev(struct hci_dev *hdev)
 		hci_dev_set_flag(hdev, HCI_BREDR_ENABLED);
 	}
 
-	write_lock(&hci_dev_list_lock);
+	write_lock_bh(&hci_dev_list_lock);
 	list_add(&hdev->list, &hci_dev_list);
-	write_unlock(&hci_dev_list_lock);
+	write_unlock_bh(&hci_dev_list_lock);
 
 	/* Devices that are marked for raw-only usage are unconfigured
 	 * and should not be included in normal operation.
@@ -2720,9 +2720,9 @@ void hci_unregister_dev(struct hci_dev *hdev)
 	hci_dev_set_flag(hdev, HCI_UNREGISTER);
 	mutex_unlock(&hdev->unregister_lock);
 
-	write_lock(&hci_dev_list_lock);
+	write_lock_bh(&hci_dev_list_lock);
 	list_del(&hdev->list);
-	write_unlock(&hci_dev_list_lock);
+	write_unlock_bh(&hci_dev_list_lock);
 
 	cancel_work_sync(&hdev->power_on);
 
-- 
2.17.1

RE: Bluetooth: hci_core: fix potential deadlock on &hci_dev_list_lock

[bluez.test.bot]

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Dear submitter,

Thank you for submitting the patches to the linux bluetooth mailing list.
This is a CI test results with your patch series:
PW Link:https://patchwork.kernel.org/project/bluetooth/list/?series=788180

---Test result---

Test Summary:
CheckPatch                    PASS      0.72 seconds
GitLint                       PASS      0.35 seconds
SubjectPrefix                 PASS      0.13 seconds
BuildKernel                   PASS      34.14 seconds
CheckAllWarning               PASS      36.80 seconds
CheckSparse                   PASS      42.36 seconds
CheckSmatch                   PASS      114.53 seconds
BuildKernel32                 PASS      32.74 seconds
TestRunnerSetup               PASS      501.56 seconds
TestRunner_l2cap-tester       PASS      31.05 seconds
TestRunner_iso-tester         PASS      52.30 seconds
TestRunner_bnep-tester        PASS      10.54 seconds
TestRunner_mgmt-tester        PASS      224.86 seconds
TestRunner_rfcomm-tester      PASS      16.31 seconds
TestRunner_sco-tester         PASS      19.87 seconds
TestRunner_ioctl-tester       PASS      18.49 seconds
TestRunner_mesh-tester        PASS      13.49 seconds
TestRunner_smp-tester         PASS      14.55 seconds
TestRunner_userchan-tester    PASS      11.30 seconds
IncrementalBuild              PASS      31.30 seconds



---
Regards,
Linux Bluetooth