linux-kernel - [PATCH v1] Bluetooth: hci_sync: fix double free in 'hci_discovery_filter

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Message-ID: <4e1578fb-c81d-fe9c-1aa1-26b6016866eb@salutedevices.com>
Date: Wed, 11 Jun 2025 19:31:49 +0300
From: Arseniy Krasnov <avkrasnov@...utedevices.com>
To: Marcel Holtmann <marcel@...tmann.org>, Luiz Augusto von Dentz
	<luiz.dentz@...il.com>
CC: <oxffffaa@...il.com>, <kernel@...utedevices.com>,
	<linux-bluetooth@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: [PATCH v1] Bluetooth: hci_sync: fix double free in
 'hci_discovery_filter_clear()'

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 call  'hci_update_passive_scan_sync()' in
'update_passive_scan_sync()'. 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-sdkernel #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 ]---

Cc: stable@...r.kernel.org
Fixes: ad383c2c65a5 ("Bluetooth: hci_sync: Enable advertising when LL privacy is enabled")
Signed-off-by: Arseniy Krasnov <avkrasnov@...utedevices.com>
---
 net/bluetooth/hci_sync.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/net/bluetooth/hci_sync.c b/net/bluetooth/hci_sync.c
index e56b1cbedab90..61a9922eb820d 100644
--- a/net/bluetooth/hci_sync.c
+++ b/net/bluetooth/hci_sync.c
@@ -3167,7 +3167,15 @@ int hci_update_scan(struct hci_dev *hdev)
 
 static int update_passive_scan_sync(struct hci_dev *hdev, void *data)
 {
-	return hci_update_passive_scan_sync(hdev);
+	int ret;
+
+	hci_dev_lock(hdev);
+
+	ret = hci_update_passive_scan_sync(hdev);
+
+	hci_dev_unlock(hdev);
+
+	return ret;
 }
 
 int hci_update_passive_scan(struct hci_dev *hdev)
-- 
2.30.1