Bluetooth: Fix atomicity violation in {conn,adv}_{min,max}_interval_set

Commit Message

Gui-Dong Han Dec. 22, 2023, 10:55 a.m. UTC

In {conn,adv}_min_interval_set():
	if (val < ... || val > ... || val > hdev->le_{conn,adv}_max_interval)
		return -EINVAL;
	hci_dev_lock(hdev);
	hdev->le_{conn,adv}_min_interval = val;
	hci_dev_unlock(hdev);

In {conn,adv}_max_interval_set():
	if (val < ... || val > ... || val < hdev->le_{conn,adv}_min_interval)
		return -EINVAL;
	hci_dev_lock(hdev);
	hdev->le_{conn,adv}_max_interval
	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: 3a5c82b78fd28 ("Bluetooth: Move LE debugfs file creation into ...")
Cc: [e-mail]
Reported-by: BassCheck <[e-mail]>
Signed-off-by: Gui-Dong Han <[e-mail]>
---
 net/bluetooth/hci_debugfs.c | 30 +++++++++++++++++++-----------
 1 file changed, 19 insertions(+), 11 deletions(-)

Comments

[e-mail] Dec. 22, 2023, 11:31 a.m. UTC | #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=812452

---Test result---

Test Summary:
CheckPatch                    FAIL      0.79 seconds
GitLint                       FAIL      4.01 seconds
SubjectPrefix                 PASS      0.35 seconds
BuildKernel                   PASS      28.00 seconds
CheckAllWarning               PASS      30.53 seconds
CheckSparse                   PASS      35.88 seconds
CheckSmatch                   PASS      104.39 seconds
BuildKernel32                 PASS      26.97 seconds
TestRunnerSetup               PASS      434.35 seconds
TestRunner_l2cap-tester       PASS      23.45 seconds
TestRunner_iso-tester         PASS      46.45 seconds
TestRunner_bnep-tester        PASS      7.35 seconds
TestRunner_mgmt-tester        FAIL      168.91 seconds
TestRunner_rfcomm-tester      PASS      11.21 seconds
TestRunner_sco-tester         PASS      14.81 seconds
TestRunner_ioctl-tester       PASS      12.41 seconds
TestRunner_mesh-tester        PASS      9.02 seconds
TestRunner_smp-tester         PASS      9.93 seconds
TestRunner_userchan-tester    PASS      7.40 seconds
IncrementalBuild              PASS      26.56 seconds

Details
##############################
Test: CheckPatch - FAIL
Desc: Run checkpatch.pl script
Output:
Bluetooth: Fix atomicity violation in {conn,adv}_{min,max}_interval_set
WARNING: Please use correct Fixes: style 'Fixes: <12 chars of sha1> ("<title line>")' - ie: 'Fixes:  ("Bluetooth: Move LE debugfs file creation into ...")'
#121: 
Fixes: 3a5c82b78fd28 ("Bluetooth: Move LE debugfs file creation into ...")

WARNING: Reported-by: should be immediately followed by Closes: with a URL to the report
#123: 
Reported-by: BassCheck <[e-mail]>
Signed-off-by: Gui-Dong Han <[e-mail]>

ERROR: trailing whitespace
#139: FILE: net/bluetooth/hci_debugfs.c:852:
+^I$

ERROR: trailing whitespace
#142: FILE: net/bluetooth/hci_debugfs.c:855:
+^I^Ihci_dev_unlock(hdev);^I$

ERROR: trailing whitespace
#156: FILE: net/bluetooth/hci_debugfs.c:882:
+^I$

ERROR: trailing whitespace
#173: FILE: net/bluetooth/hci_debugfs.c:996:
+^I$

ERROR: trailing whitespace
#176: FILE: net/bluetooth/hci_debugfs.c:999:
+^I^Ihci_dev_unlock(hdev);^I$

total: 5 errors, 2 warnings, 0 checks, 62 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/13503199.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 {conn,adv}_{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 < ... || val > ... || val > hdev->le_{conn,adv}_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->le_{conn,adv}_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 < ... || val > ... || val < hdev->le_{conn,adv}_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->le_{conn,adv}_max_interval"
15: B3 Line contains hard tab characters (\t): "	hci_dev_unlock(hdev);"
##############################
Test: TestRunner_mgmt-tester - FAIL
Desc: Run mgmt-tester with test-runner
Output:
Total: 497, Passed: 495 (99.6%), Failed: 1, Not Run: 1

Failed Test Cases
LL Privacy - Start Discovery 2 (Disable RL)          Failed       0.336 seconds


---
Regards,
Linux Bluetooth

David Laight Dec. 22, 2023, 11:41 a.m. UTC | #2

From: Gui-Dong Han
> Sent: 22 December 2023 10:55
> 
> In {conn,adv}_min_interval_set():
> 	if (val < ... || val > ... || val > hdev->le_{conn,adv}_max_interval)
> 		return -EINVAL;
> 	hci_dev_lock(hdev);
> 	hdev->le_{conn,adv}_min_interval = val;
> 	hci_dev_unlock(hdev);
> 
> In {conn,adv}_max_interval_set():
> 	if (val < ... || val > ... || val < hdev->le_{conn,adv}_min_interval)
> 		return -EINVAL;
> 	hci_dev_lock(hdev);
> 	hdev->le_{conn,adv}_max_interval
> 	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.

Your static analysis tool is basically broken.

The only possible issues are if the accesses aren't atomic.
In practise they always will be but using READ_ONCE() and
WRITE_ONCE() would make that certain.

The lock sequence:
> 	hci_dev_lock(hdev);
>  	hdev->le_conn_min_interval = val;
>  	hci_dev_unlock(hdev);
is pretty pointless - is doesn't 'lock' two+ things together.

	David

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)

Gui-Dong Han Dec. 22, 2023, 12:03 p.m. UTC | #3

Hi,

Thanks for your feedback. Let me clarify the potential issue with 
concurrent execution of setmax and setmin functions. Consider a scenario 
where setmin writes a new, valid 'min' value, and concurrently, setmax 
writes a value that is greater than the old 'min' but smaller than the 
new 'min'. In this case, setmax might check against the old 'min' value 
(before acquiring the lock) but write its value after the 'min' has been 
updated by setmin. This leads to a situation where the 'max' value ends 
up being smaller than the 'min' value, which is an inconsistency.

Regarding the lock sequence you mentioned, it's indeed from the original 
code. My patch aims to include the validity checks within the 
lock/unlock sequence to prevent the described race condition.

Thanks,
Han

On 22/12/2023 下午7:41, David Laight wrote:
> From: Gui-Dong Han
>> Sent: 22 December 2023 10:55
>>
>> In {conn,adv}_min_interval_set():
>> 	if (val < ... || val > ... || val > hdev->le_{conn,adv}_max_interval)
>> 		return -EINVAL;
>> 	hci_dev_lock(hdev);
>> 	hdev->le_{conn,adv}_min_interval = val;
>> 	hci_dev_unlock(hdev);
>>
>> In {conn,adv}_max_interval_set():
>> 	if (val < ... || val > ... || val < hdev->le_{conn,adv}_min_interval)
>> 		return -EINVAL;
>> 	hci_dev_lock(hdev);
>> 	hdev->le_{conn,adv}_max_interval
>> 	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.
> Your static analysis tool is basically broken.
>
> The only possible issues are if the accesses aren't atomic.
> In practise they always will be but using READ_ONCE() and
> WRITE_ONCE() would make that certain.
>
> The lock sequence:
>> 	hci_dev_lock(hdev);
>>   	hdev->le_conn_min_interval = val;
>>   	hci_dev_unlock(hdev);
> is pretty pointless - is doesn't 'lock' two+ things together.
>
> 	David
>
> -
> Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
> Registration No: 1397386 (Wales)
>

Patch

diff --git a/net/bluetooth/hci_debugfs.c b/net/bluetooth/hci_debugfs.c
index 6b7741f6e95b..6fdda807f2cf 100644
--- a/net/bluetooth/hci_debugfs.c
+++ b/net/bluetooth/hci_debugfs.c
@@ -849,11 +849,13 @@  DEFINE_SHOW_ATTRIBUTE(long_term_keys);
 static int conn_min_interval_set(void *data, u64 val)
 {
 	struct hci_dev *hdev = data;
-
-	if (val < 0x0006 || val > 0x0c80 || val > hdev->le_conn_max_interval)
+	
+	hci_dev_lock(hdev);
+	if (val < 0x0006 || val > 0x0c80 || val > hdev->le_conn_max_interval) {
+		hci_dev_unlock(hdev);	
 		return -EINVAL;
+	}
 
-	hci_dev_lock(hdev);
 	hdev->le_conn_min_interval = val;
 	hci_dev_unlock(hdev);
 
@@ -877,11 +879,13 @@  DEFINE_DEBUGFS_ATTRIBUTE(conn_min_interval_fops, conn_min_interval_get,
 static int conn_max_interval_set(void *data, u64 val)
 {
 	struct hci_dev *hdev = data;
-
-	if (val < 0x0006 || val > 0x0c80 || val < hdev->le_conn_min_interval)
+	
+	hci_dev_lock(hdev);
+	if (val < 0x0006 || val > 0x0c80 || val < hdev->le_conn_min_interval) {
+		hci_dev_unlock(hdev);
 		return -EINVAL;
+	}
 
-	hci_dev_lock(hdev);
 	hdev->le_conn_max_interval = val;
 	hci_dev_unlock(hdev);
 
@@ -989,11 +993,13 @@  DEFINE_DEBUGFS_ATTRIBUTE(adv_channel_map_fops, adv_channel_map_get,
 static int adv_min_interval_set(void *data, u64 val)
 {
 	struct hci_dev *hdev = data;
-
-	if (val < 0x0020 || val > 0x4000 || val > hdev->le_adv_max_interval)
+	
+	hci_dev_lock(hdev);
+	if (val < 0x0020 || val > 0x4000 || val > hdev->le_adv_max_interval) {
+		hci_dev_unlock(hdev);	
 		return -EINVAL;
+	}
 
-	hci_dev_lock(hdev);
 	hdev->le_adv_min_interval = val;
 	hci_dev_unlock(hdev);
 
@@ -1018,10 +1024,12 @@  static int adv_max_interval_set(void *data, u64 val)
 {
 	struct hci_dev *hdev = data;
 
-	if (val < 0x0020 || val > 0x4000 || val < hdev->le_adv_min_interval)
+	hci_dev_lock(hdev);
+	if (val < 0x0020 || val > 0x4000 || val < hdev->le_adv_min_interval) {
+		hci_dev_unlock(hdev);
 		return -EINVAL;
+	}
 
-	hci_dev_lock(hdev);
 	hdev->le_adv_max_interval = val;
 	hci_dev_unlock(hdev);