Bluetooth: Fix atomicity violation in sniff_{min,max}_interval_set

In sniff_min_interval_set():

	if (val == 0 || val % 2 || val > hdev->sniff_max_interval)
		return -EINVAL;
	hci_dev_lock(hdev);
	hdev->sniff_min_interval = val;
	hci_dev_unlock(hdev);

In sniff_max_interval_set():

	if (val == 0 || val % 2 || val < hdev->sniff_min_interval)
		return -EINVAL;
	hci_dev_lock(hdev);
	hdev->sniff_max_interval = 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/

---
 net/bluetooth/hci_debugfs.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

index 6b7741f6e95b..f032fdf8f481 100644
@@ -566,11 +566,13 @@ DEFINE_DEBUGFS_ATTRIBUTE(idle_timeout_fops, idle_timeout_get,
 static int sniff_min_interval_set(void *data, u64 val)
 {
 	struct hci_dev *hdev = data;
-
-	if (val == 0 || val % 2 || val > hdev->sniff_max_interval)
+	
+	hci_dev_lock(hdev);
+	if (val == 0 || val % 2 || val > hdev->sniff_max_interval) {
+		hci_dev_unlock(hdev);
 		return -EINVAL;
+	}
 
-	hci_dev_lock(hdev);
 	hdev->sniff_min_interval = val;
 	hci_dev_unlock(hdev);
 

@@ -594,11 +596,13 @@ DEFINE_DEBUGFS_ATTRIBUTE(sniff_min_interval_fops, sniff_min_interval_get,
 static int sniff_max_interval_set(void *data, u64 val)
 {
 	struct hci_dev *hdev = data;
-
-	if (val == 0 || val % 2 || val < hdev->sniff_min_interval)
+	
+	hci_dev_lock(hdev);
+	if (val == 0 || val % 2 || val < hdev->sniff_min_interval) {
+		hci_dev_unlock(hdev);
 		return -EINVAL;
+	}
 
-	hci_dev_lock(hdev);
 	hdev->sniff_max_interval = val;
 	hci_dev_unlock(hdev);
 

2.34.1

This is automated email and please do not reply to this email!

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=812454

---Test result---

Test Summary:

CheckPatch                    FAIL      0.87 seconds
GitLint                       FAIL      0.54 seconds
SubjectPrefix                 PASS      0.11 seconds
BuildKernel                   PASS      27.99 seconds
CheckAllWarning               PASS      30.59 seconds
CheckSparse                   PASS      36.70 seconds
CheckSmatch                   PASS      99.88 seconds
BuildKernel32                 PASS      27.27 seconds
TestRunnerSetup               PASS      435.93 seconds
TestRunner_l2cap-tester       PASS      24.38 seconds
TestRunner_iso-tester         PASS      45.43 seconds
TestRunner_bnep-tester        PASS      7.00 seconds
TestRunner_mgmt-tester        PASS      162.68 seconds
TestRunner_rfcomm-tester      PASS      10.90 seconds
TestRunner_sco-tester         PASS      14.56 seconds
TestRunner_ioctl-tester       PASS      12.27 seconds
TestRunner_mesh-tester        PASS      9.95 seconds
TestRunner_smp-tester         PASS      9.78 seconds
TestRunner_userchan-tester    PASS      7.37 seconds
IncrementalBuild              PASS      26.28 seconds

Details
##############################
Test: CheckPatch - FAIL
Desc: Run checkpatch.pl script
Output:
Bluetooth: Fix atomicity violation in sniff_{min,max}_interval_set
WARNING: Please use correct Fixes: style 'Fixes: <12 chars of sha1> ("<title line>")' - ie: 'Fixes: ("Bluetooth: Move BR/EDR debugfs file creation ...")' #121:

WARNING: Reported-by: should be immediately followed by Closes: with a URL to the report #123:

ERROR: trailing whitespace
#139: FILE: net/bluetooth/hci_debugfs.c:569:
+^I$

ERROR: trailing whitespace
#156: FILE: net/bluetooth/hci_debugfs.c:599:
+^I$

total: 2 errors, 2 warnings, 0 checks, 32 lines checked

NOTE: For some of the reported defects, checkpatch may be able to
mechanically convert to the typical style using --fix or --fix-inplace.

NOTE: Whitespace errors detected.
You may wish to use scripts/cleanpatch or scripts/cleanfile

/github/workspace/src/src/13503201.patch has style problems, please review.

NOTE: Ignored message types: UNKNOWN_COMMIT_ID

NOTE: If any of the errors are false positives, please report
them to the maintainer, see CHECKPATCH in MAINTAINERS.

Use of uninitialized value $cid in concatenation (.) or string at /github/workspace/src/src/scripts/checkpatch.pl line 3228.
##############################
Test: GitLint - FAIL
Desc: Run gitlint
Output:
Bluetooth: Fix atomicity violation in sniff_{min,max}_interval_set

WARNING: I3 - ignore-body-lines: gitlint will be switching from using Python regex 'match' (match beginning) to 'search' (match anywhere) semantics. Please review your ignore-body-lines.regex option accordingly. To remove this warning, set general.regex-style-search=True. More details: https://jorisroovers.github.io/gitlint/configuration/#regex-style-search
4: B3 Line contains hard tab characters (\t): " if (val == 0 || val % 2 || val > hdev->sniff_max_interval)"
5: B3 Line contains hard tab characters (\t): " return -EINVAL;"
6: B3 Line contains hard tab characters (\t): " hci_dev_lock(hdev);"
7: B3 Line contains hard tab characters (\t): " hdev->sniff_min_interval = val;"
8: B3 Line contains hard tab characters (\t): " hci_dev_unlock(hdev);"
11: B3 Line contains hard tab characters (\t): " if (val == 0 || val % 2 || val < hdev->sniff_min_interval)"
12: B3 Line contains hard tab characters (\t): " return -EINVAL;"
13: B3 Line contains hard tab characters (\t): " hci_dev_lock(hdev);"
14: B3 Line contains hard tab characters (\t): " hdev->sniff_max_interval = val;"
15: B3 Line contains hard tab characters (\t): " hci_dev_unlock(hdev);"

---
Regards,
Linux Bluetooth