[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: [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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