Re: [PATCH v1] Bluetooth: hci_sync: fix double free in 'hci_discovery_filter_clear()'

[Arseniy Krasnov <avkrasnov@salutedevices.com>]

On 12.06.2025 16:12, Luiz Augusto von Dentz wrote:
> Hi Arseniy,
> 
> On Wed, Jun 11, 2025 at 12:31 PM Arseniy Krasnov
> <avkrasnov@salutedevices.com> 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()'
>>
>>    '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@vger.kernel.org
>> Fixes: ad383c2c65a5 ("Bluetooth: hci_sync: Enable advertising when LL privacy is enabled")
>> Signed-off-by: Arseniy Krasnov <avkrasnov@salutedevices.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;
> 
> This deadlocks since it is a callback on hci_cmd_sync_work which shall
> never use hci_dev_lock while waiting for events processed by
> hci_event_packet which will attempt to do:
> 
>     hci_dev_lock(hdev);
>     kfree_skb(hdev->recv_event);
>     hdev->recv_event = skb_clone(skb, GFP_KERNEL);
>     hci_dev_unlock(hdev);
> 
> This is why there are no test results because all tests seem to be failing now:

Thanks,

ahhhh, may be more valid solution will be to add spinlock to 'struct discovery_state', which protects
operations on this structure at least in 'hci_discovery_filter_clear()' ? 

Thanks, Arseniy

> 
> https://github.com/BluezTestBot/bluetooth-next/pull/2884
> 
>>  }
>>
>>  int hci_update_passive_scan(struct hci_dev *hdev)
>> --
>> 2.30.1
>>
> 
>