[PATCH v4] Bluetooth: hci_sync: fix double free in 'hci_discovery_filter_clear()'

[PATCH v4] Bluetooth: hci_sync: fix double free in 'hci_discovery_filter_clear()'

[Arseniy Krasnov]

Function 'hci_discovery_filter_clear()' frees 'uuids' array and then
sets it to NULL. There is a tiny chance of the following race:

'hci_cmd_sync_work()'

 'update_passive_scan_sync()'

   'hci_update_passive_scan_sync()'

     'hci_discovery_filter_clear()'
       kfree(uuids);

       <-------------------------preempted-------------------------------->
                                           'start_service_discovery()'

                                             'hci_discovery_filter_clear()'
                                               kfree(uuids); // DOUBLE FREE

       <-------------------------preempted-------------------------------->

      uuids = NULL;

To fix it let's add locking around 'kfree()' call and NULL pointer
assignment. Otherwise the following backtrace fires:

[ ] ------------[ cut here ]------------
[ ] kernel BUG at mm/slub.c:547!
[ ] Internal error: Oops - BUG: 00000000f2000800 [#1] PREEMPT SMP
[ ] CPU: 3 UID: 0 PID: 246 Comm: bluetoothd Tainted: G O 6.12.19-kernel #1
[ ] Tainted: [O]=OOT_MODULE
[ ] pstate: 60400005 (nZCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
[ ] pc : __slab_free+0xf8/0x348
[ ] lr : __slab_free+0x48/0x348
...
[ ] Call trace:
[ ]  __slab_free+0xf8/0x348
[ ]  kfree+0x164/0x27c
[ ]  start_service_discovery+0x1d0/0x2c0
[ ]  hci_sock_sendmsg+0x518/0x924
[ ]  __sock_sendmsg+0x54/0x60
[ ]  sock_write_iter+0x98/0xf8
[ ]  do_iter_readv_writev+0xe4/0x1c8
[ ]  vfs_writev+0x128/0x2b0
[ ]  do_writev+0xfc/0x118
[ ]  __arm64_sys_writev+0x20/0x2c
[ ]  invoke_syscall+0x68/0xf0
[ ]  el0_svc_common.constprop.0+0x40/0xe0
[ ]  do_el0_svc+0x1c/0x28
[ ]  el0_svc+0x30/0xd0
[ ]  el0t_64_sync_handler+0x100/0x12c
[ ]  el0t_64_sync+0x194/0x198
[ ] Code: 8b0002e6 eb17031f 54fffbe1 d503201f (d4210000)
[ ] ---[ end trace 0000000000000000 ]---

Fixes: ad383c2c65a5 ("Bluetooth: hci_sync: Enable advertising when LL privacy is enabled")
Signed-off-by: Arseniy Krasnov <avkrasnov@salutedevices.com>
---
 Changelog v1->v2:
 * Don't call 'hci_dev_lock()' in 'update_passive_scan_sync()' as it
   triggers deadlock. Instead of that - add spinlock which protects
   freeing code.
 Changelog v2->v3:
 * Rebase on current 'bluetooth' repo due to fuzz.
 Changelog v3->v4:
 * Rebase on current 'bluetooth' repo due patch apply failed.

 include/net/bluetooth/hci_core.h | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/include/net/bluetooth/hci_core.h b/include/net/bluetooth/hci_core.h
index 1ef9279cfd6f..3728495f0819 100644
--- a/include/net/bluetooth/hci_core.h
+++ b/include/net/bluetooth/hci_core.h
@@ -29,6 +29,7 @@
 #include <linux/idr.h>
 #include <linux/leds.h>
 #include <linux/rculist.h>
+#include <linux/spinlock.h>
 #include <linux/srcu.h>
 
 #include <net/bluetooth/hci.h>
@@ -94,6 +95,7 @@ struct discovery_state {
 	u16			uuid_count;
 	u8			(*uuids)[16];
 	unsigned long		name_resolve_timeout;
+	spinlock_t		lock;
 };
 
 #define SUSPEND_NOTIFIER_TIMEOUT	msecs_to_jiffies(2000) /* 2 seconds */
@@ -889,6 +891,7 @@ static inline void iso_recv(struct hci_conn *hcon, struct sk_buff *skb,
 
 static inline void discovery_init(struct hci_dev *hdev)
 {
+	spin_lock_init(&hdev->discovery.lock);
 	hdev->discovery.state = DISCOVERY_STOPPED;
 	INIT_LIST_HEAD(&hdev->discovery.all);
 	INIT_LIST_HEAD(&hdev->discovery.unknown);
@@ -903,8 +906,11 @@ static inline void hci_discovery_filter_clear(struct hci_dev *hdev)
 	hdev->discovery.report_invalid_rssi = true;
 	hdev->discovery.rssi = HCI_RSSI_INVALID;
 	hdev->discovery.uuid_count = 0;
+
+	spin_lock(&hdev->discovery.lock);
 	kfree(hdev->discovery.uuids);
 	hdev->discovery.uuids = NULL;
+	spin_unlock(&hdev->discovery.lock);
 }
 
 bool hci_discovery_active(struct hci_dev *hdev);
-- 
2.43.0

RE: [v4] Bluetooth: hci_sync: fix double free in 'hci_discovery_filter_clear()'

[bluez.test.bot]

[-- Attachment #1: Type: text/plain, Size: 2295 bytes --]

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=983081

---Test result---

Test Summary:
CheckPatch                    PENDING   0.18 seconds
GitLint                       PENDING   0.17 seconds
SubjectPrefix                 PASS      0.12 seconds
BuildKernel                   PASS      23.85 seconds
CheckAllWarning               PASS      26.49 seconds
CheckSparse                   PASS      29.97 seconds
BuildKernel32                 PASS      24.02 seconds
TestRunnerSetup               PASS      469.91 seconds
TestRunner_l2cap-tester       PASS      27.17 seconds
TestRunner_iso-tester         PASS      36.04 seconds
TestRunner_bnep-tester        PASS      5.94 seconds
TestRunner_mgmt-tester        FAIL      132.92 seconds
TestRunner_rfcomm-tester      PASS      9.35 seconds
TestRunner_sco-tester         PASS      14.77 seconds
TestRunner_ioctl-tester       PASS      9.82 seconds
TestRunner_mesh-tester        FAIL      11.42 seconds
TestRunner_smp-tester         PASS      8.60 seconds
TestRunner_userchan-tester    PASS      6.50 seconds
IncrementalBuild              PENDING   0.81 seconds

Details
##############################
Test: CheckPatch - PENDING
Desc: Run checkpatch.pl script
Output:

##############################
Test: GitLint - PENDING
Desc: Run gitlint
Output:

##############################
Test: TestRunner_mgmt-tester - FAIL
Desc: Run mgmt-tester with test-runner
Output:
Total: 490, Passed: 485 (99.0%), Failed: 1, Not Run: 4

Failed Test Cases
LL Privacy - Set Flags 3 (2 Devices to RL)           Failed       0.210 seconds
##############################
Test: TestRunner_mesh-tester - FAIL
Desc: Run mesh-tester with test-runner
Output:
Total: 10, Passed: 8 (80.0%), Failed: 2, Not Run: 0

Failed Test Cases
Mesh - Send cancel - 1                               Timed out    2.114 seconds
Mesh - Send cancel - 2                               Timed out    1.993 seconds
##############################
Test: IncrementalBuild - PENDING
Desc: Incremental build with the patches in the series
Output:



---
Regards,
Linux Bluetooth

Re: [PATCH v4] Bluetooth: hci_sync: fix double free in 'hci_discovery_filter_clear()'

[patchwork-bot+bluetooth]

Hello:

This patch was applied to bluetooth/bluetooth-next.git (master)
by Luiz Augusto von Dentz <luiz.von.dentz@intel.com>:

On Wed, 16 Jul 2025 22:23:58 +0300 you wrote:
> Function 'hci_discovery_filter_clear()' frees 'uuids' array and then
> sets it to NULL. There is a tiny chance of the following race:
> 
> 'hci_cmd_sync_work()'
> 
>  'update_passive_scan_sync()'
> 
> [...]

Here is the summary with links:
  - [v4] Bluetooth: hci_sync: fix double free in 'hci_discovery_filter_clear()'
    https://git.kernel.org/bluetooth/bluetooth-next/c/dd8174bd527e

You are awesome, thank you!
-- 
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