[PATCH] Bluetooth: 6lowpan: avoid untracked enable work

[PATCH] Bluetooth: 6lowpan: avoid untracked enable work

[Cen Zhang]

lowpan_enable_set() allocates a temporary work item and schedules
do_enable_set() on system_wq, then returns to debugfs. The debugfs active
operation has ended at that point, but the worker still executes module
text and manipulates enable_6lowpan and listen_chan.

bt_6lowpan_exit() removes the debugfs files and immediately closes and
puts listen_chan. It has no pointer to the queued work item, so it cannot
cancel or flush it before tearing down the state that the worker uses.

The buggy scenario involves two paths, with each column showing the order
within that path:

debugfs enable write              module exit
1. lowpan_enable_set() allocates  1. bt_6lowpan_exit() removes
   set_enable work                   the debugfs file
2. schedule_work() queues         2. bt_6lowpan_exit() closes
   do_enable_set()                   and puts listen_chan
3. the write operation returns    3. module teardown can continue
4. do_enable_set() later runs
   against stale state

Run the enable state transition synchronously in lowpan_enable_set()
instead. The simple debugfs setter can sleep, and this file already handles
the 6LoWPAN control write synchronously under the same set_lock. Once the
setter returns, debugfs removal covers the whole operation and exit can no
longer race with an untracked work item.

Validation reproduced this kernel report:
BUG: KASAN: slab-use-after-free in do_enable_set+0x113/0x2e0
Workqueue: events do_enable_set [bluetooth_6lowpan]
The buggy address belongs to the object at ffff888109cb8000

Fixes: 90305829635d ("Bluetooth: 6lowpan: Converting rwlocks to use RCU")
Assisted-by: Codex:gpt-5.5
Signed-off-by: Cen Zhang <zzzccc427@gmail.com>
---
 net/bluetooth/6lowpan.c | 27 ++++-----------------------
 1 file changed, 4 insertions(+), 23 deletions(-)

diff --git a/net/bluetooth/6lowpan.c b/net/bluetooth/6lowpan.c
index cb1e329d66fd..249feca42501 100644
--- a/net/bluetooth/6lowpan.c
+++ b/net/bluetooth/6lowpan.c
@@ -1093,23 +1093,15 @@ static void disconnect_all_peers(void)
 	} while (nchans);
 }
 
-struct set_enable {
-	struct work_struct work;
-	bool flag;
-};
-
-static void do_enable_set(struct work_struct *work)
+static void do_enable_set(bool flag)
 {
-	struct set_enable *set_enable = container_of(work,
-						     struct set_enable, work);
-
-	if (!set_enable->flag || enable_6lowpan != set_enable->flag)
+	if (!flag || enable_6lowpan != flag)
 		/* Disconnect existing connections if 6lowpan is
 		 * disabled
 		 */
 		disconnect_all_peers();
 
-	enable_6lowpan = set_enable->flag;
+	enable_6lowpan = flag;
 
 	mutex_lock(&set_lock);
 	if (listen_chan) {
@@ -1121,22 +1113,11 @@ static void do_enable_set(struct work_struct *work)
 
 	listen_chan = bt_6lowpan_listen();
 	mutex_unlock(&set_lock);
-
-	kfree(set_enable);
 }
 
 static int lowpan_enable_set(void *data, u64 val)
 {
-	struct set_enable *set_enable;
-
-	set_enable = kzalloc_obj(*set_enable);
-	if (!set_enable)
-		return -ENOMEM;
-
-	set_enable->flag = !!val;
-	INIT_WORK(&set_enable->work, do_enable_set);
-
-	schedule_work(&set_enable->work);
+	do_enable_set(!!val);
 
 	return 0;
 }
-- 
2.43.0

RE: Bluetooth: 6lowpan: avoid untracked enable work

[bluez.test.bot]

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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=1115489

---Test result---

Test Summary:
CheckPatch                    PASS      1.09 seconds
VerifyFixes                   PASS      0.21 seconds
VerifySignedoff               PASS      0.20 seconds
GitLint                       PASS      0.55 seconds
SubjectPrefix                 PASS      0.21 seconds
BuildKernel                   PASS      25.67 seconds
CheckAllWarning               PASS      29.14 seconds
CheckSparse                   PASS      28.07 seconds
BuildKernel32                 PASS      25.73 seconds
CheckKernelLLVM               SKIP      0.00 seconds
TestRunnerSetup               PASS      540.18 seconds
TestRunner_6lowpan-tester     PASS      22.55 seconds
IncrementalBuild              PASS      24.29 seconds

Details
##############################
Test: CheckKernelLLVM - SKIP
Desc: Build kernel with LLVM + context analysis
Output:
Clang not found


https://github.com/bluez/bluetooth-next/pull/340

---
Regards,
Linux Bluetooth