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* [PATCH] Bluetooth: Fix atomicity violation in conn_info_{min,max}_age_set
@ 2023-12-22 11:04 Gui-Dong Han
  2023-12-22 11:32 ` bluez.test.bot
  0 siblings, 1 reply; 2+ messages in thread
From: Gui-Dong Han @ 2023-12-22 11:04 UTC (permalink / raw)
  To: marcel, johan.hedberg, luiz.dentz
  Cc: linux-bluetooth, linux-kernel, baijiaju1990, Gui-Dong Han, stable,
	BassCheck

In conn_info_min_age_set():
	if (val == 0 || val > hdev->conn_info_max_age)
		return -EINVAL;
	hci_dev_lock(hdev);
	hdev->conn_info_min_age = val;
	hci_dev_unlock(hdev);

In conn_info_max_age_set():
	if (val == 0 || val < hdev->conn_info_min_age)
		return -EINVAL;
	hci_dev_lock(hdev);
	hdev->conn_info_max_age = val;
	hci_dev_unlock(hdev);

The atomicity violation occurs due to concurrent execution of set_min and
set_max funcs which may lead to inconsistent reads and writes of the min
value and the max value. The checks for value validity are ineffective as
the min/max values could change immediately after being checked, raising
the risk of the min value being greater than the max value and causing
invalid settings.

This possible bug is found by an experimental static analysis tool
developed by our team, BassCheck[1]. This tool analyzes the locking APIs
to extract function pairs that can be concurrently executed, and then
analyzes the instructions in the paired functions to identify possible
concurrency bugs including data races and atomicity violations. The above
possible bug is reported when our tool analyzes the source code of
Linux 5.17.

To resolve this issue, it is suggested to encompass the validity checks
within the locked sections in both set_min and set_max funcs. The
modification ensures that the validation of 'val' against the
current min/max values is atomic, thus maintaining the integrity of the
settings. With this patch applied, our tool no longer reports the bug,
with the kernel configuration allyesconfig for x86_64. Due to the lack of
associated hardware, we cannot test the patch in runtime testing, and just
verify it according to the code logic.

[1] https://sites.google.com/view/basscheck/

Fixes: 40ce72b1951c5 ("Bluetooth: Move common debugfs file creation ...")
Cc: stable@vger.kernel.org
Reported-by: BassCheck <bass@buaa.edu.cn>
Signed-off-by: Gui-Dong Han <2045gemini@gmail.com>
---
 net/bluetooth/hci_debugfs.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/net/bluetooth/hci_debugfs.c b/net/bluetooth/hci_debugfs.c
index 6b7741f6e95b..d4ce2769c939 100644
--- a/net/bluetooth/hci_debugfs.c
+++ b/net/bluetooth/hci_debugfs.c
@@ -217,11 +217,13 @@ DEFINE_SHOW_ATTRIBUTE(remote_oob);
 static int conn_info_min_age_set(void *data, u64 val)
 {
 	struct hci_dev *hdev = data;
-
-	if (val == 0 || val > hdev->conn_info_max_age)
+	
+	hci_dev_lock(hdev);
+	if (val == 0 || val > hdev->conn_info_max_age) {
+		hci_dev_unlock(hdev);
 		return -EINVAL;
+	}
 
-	hci_dev_lock(hdev);
 	hdev->conn_info_min_age = val;
 	hci_dev_unlock(hdev);
 
@@ -245,11 +247,13 @@ DEFINE_DEBUGFS_ATTRIBUTE(conn_info_min_age_fops, conn_info_min_age_get,
 static int conn_info_max_age_set(void *data, u64 val)
 {
 	struct hci_dev *hdev = data;
-
-	if (val == 0 || val < hdev->conn_info_min_age)
+	
+	hci_dev_lock(hdev);
+	if (val == 0 || val < hdev->conn_info_min_age) {
+		hci_dev_unlock(hdev);
 		return -EINVAL;
+	}
 
-	hci_dev_lock(hdev);
 	hdev->conn_info_max_age = val;
 	hci_dev_unlock(hdev);
 
-- 
2.34.1


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2023-12-22 11:04 [PATCH] Bluetooth: Fix atomicity violation in conn_info_{min,max}_age_set Gui-Dong Han
2023-12-22 11:32 ` bluez.test.bot

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