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From:   Ying Hsu <yinghsu@chromium.org>
To:     linux-bluetooth@vger.kernel.org
Cc:     chromeos-bluetooth-upstreaming@chromium.org,
        Ying Hsu <yinghsu@chromium.org>,
        Johan Hedberg <johan.hedberg@gmail.com>,
        Luiz Augusto von Dentz <luiz.dentz@gmail.com>,
        Marcel Holtmann <marcel@holtmann.org>,
        linux-kernel@vger.kernel.org
Subject: [PATCH] Bluetooth: Fix hci_suspend_sync crash
Date:   Wed,  5 Jul 2023 21:06:47 +0000
Message-ID: <20230705210647.1.I636c21e4dc8fe3352f4d7aef26c0ec3857e24ca0@changeid>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

If hci_unregister_dev() frees the hci_dev object but hci_suspend_notifier
may still be accessing it, it can cause the program to crash.
Here's the call trace:
  <4>[102152.653246] Call Trace:
  <4>[102152.653254]  hci_suspend_sync+0x109/0x301 [bluetooth]
  <4>[102152.653259]  hci_suspend_dev+0x78/0xcd [bluetooth]
  <4>[102152.653263]  hci_suspend_notifier+0x42/0x7a [bluetooth]
  <4>[102152.653268]  notifier_call_chain+0x43/0x6b
  <4>[102152.653271]  __blocking_notifier_call_chain+0x48/0x69
  <4>[102152.653273]  __pm_notifier_call_chain+0x22/0x39
  <4>[102152.653276]  pm_suspend+0x287/0x57c
  <4>[102152.653278]  state_store+0xae/0xe5
  <4>[102152.653281]  kernfs_fop_write+0x109/0x173
  <4>[102152.653284]  __vfs_write+0x16f/0x1a2
  <4>[102152.653287]  ? selinux_file_permission+0xca/0x16f
  <4>[102152.653289]  ? security_file_permission+0x36/0x109
  <4>[102152.653291]  vfs_write+0x114/0x21d
  <4>[102152.653293]  __x64_sys_write+0x7b/0xdb
  <4>[102152.653296]  do_syscall_64+0x59/0x194
  <4>[102152.653299]  entry_SYSCALL_64_after_hwframe+0x5c/0xc1

This patch holds the reference count of the hci_dev object while
processing it in hci_suspend_notifier to avoid potential crash
caused by the race condition.

Signed-off-by: Ying Hsu <yinghsu@chromium.org>
---
Tested with 100 times suspend/resume on a Chromebook device.

 net/bluetooth/hci_core.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/net/bluetooth/hci_core.c b/net/bluetooth/hci_core.c
index b421e196f60c..bdbe26ffbd39 100644
--- a/net/bluetooth/hci_core.c
+++ b/net/bluetooth/hci_core.c
@@ -2434,6 +2434,9 @@ static int hci_suspend_notifier(struct notifier_block *nb, unsigned long action,
 	if (hci_dev_test_flag(hdev, HCI_USER_CHANNEL))
 		return NOTIFY_DONE;
 
+	/* To avoid a potential race with hci_unregister_dev. */
+	hci_dev_hold(hdev);
+
 	if (action == PM_SUSPEND_PREPARE)
 		ret = hci_suspend_dev(hdev);
 	else if (action == PM_POST_SUSPEND)
@@ -2443,6 +2446,7 @@ static int hci_suspend_notifier(struct notifier_block *nb, unsigned long action,
 		bt_dev_err(hdev, "Suspend notifier action (%lu) failed: %d",
 			   action, ret);
 
+	hci_dev_put(hdev);
 	return NOTIFY_DONE;
 }
 
-- 
2.41.0.255.g8b1d071c50-goog