Re: [PATCH v3] tracing/net_sched: NULL pointer dereference in perf_trace_qdisc_reset()

[Yunseong Kim <yskelg@gmail.com>]

Hi Pedro,

On 6/25/24 12:12 오전, Pedro Tammela wrote:
> On 22/06/2024 01:57, yskelg@gmail.com wrote:
>> From: Yunseong Kim <yskelg@gmail.com>
>>
>> In the TRACE_EVENT(qdisc_reset) NULL dereference occurred from
>>
>>   qdisc->dev_queue->dev <NULL> ->name
>>
>> [ 5301.595872] KASAN: null-ptr-deref in range
>> [0x0000000000000130-0x0000000000000137]
>> [ 5301.595877] Mem abort info:
>> [ 5301.595881]   ESR = 0x0000000096000006
>> [ 5301.595885]   EC = 0x25: DABT (current EL), IL = 32 bits
>> [ 5301.595889]   SET = 0, FnV = 0
>> [ 5301.595893]   EA = 0, S1PTW = 0
>> [ 5301.595896]   FSC = 0x06: level 2 translation fault
>> [ 5301.595900] Data abort info:
>> [ 5301.595903]   ISV = 0, ISS = 0x00000006, ISS2 = 0x00000000
>> [ 5301.595907]   CM = 0, WnR = 0, TnD = 0, TagAccess = 0
>> [ 5301.595911]   GCS = 0, Overlay = 0, DirtyBit = 0, Xs = 0
>> [ 5301.595915] [dfff800000000026] address between user and kernel
>> address ranges
>> [ 5301.595971] Internal error: Oops: 0000000096000006 [#1] SMP
>> Link:
>> https://lore.kernel.org/lkml/20240229143432.273b4871@gandalf.local.home/t/
>> Fixes: 51270d573a8d ("tracing/net_sched: Fix tracepoints that save
>> qdisc_dev() as a string")
>> Cc: netdev@vger.kernel.org
>> Cc: stable@vger.kernel.org # +v6.7.10, +v6.8
>> Signed-off-by: Yunseong Kim <yskelg@gmail.com>
>> Signed-off-by: Yeoreum Yun <yeoreum.yun@arm.com>
>> ---
>>   include/trace/events/qdisc.h | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/include/trace/events/qdisc.h b/include/trace/events/qdisc.h
>> index f1b5e816e7e5..170b51fbe47a 100644
>> --- a/include/trace/events/qdisc.h
>> +++ b/include/trace/events/qdisc.h
>> @@ -81,7 +81,7 @@ TRACE_EVENT(qdisc_reset,
>>       TP_ARGS(q),
>>         TP_STRUCT__entry(
>> -        __string(    dev,        qdisc_dev(q)->name    )
>> +        __string(dev, qdisc_dev(q) ? qdisc_dev(q)->name : "noop_queue")
>>           __string(    kind,        q->ops->id        )
>>           __field(    u32,        parent            )
>>           __field(    u32,        handle            )
> 
> You missed the __assign_str portion (see below). Also let's just say
> "(null)" as it's the correct device name. "noop_queue" could be misleading.

Thanks for the code review Pedro, I agree your advice.

> diff --git a/include/trace/events/qdisc.h b/include/trace/events/qdisc.h
> index 1f4258308b96..f54e0b4dbcf4 100644
> --- a/include/trace/events/qdisc.h
> +++ b/include/trace/events/qdisc.h
> @@ -81,14 +81,14 @@ TRACE_EVENT(qdisc_reset,
>         TP_ARGS(q),
> 
>         TP_STRUCT__entry(
> -               __string(       dev,            qdisc_dev(q)->name      )
> +               __string(       dev,            qdisc_dev(q) ?
> qdisc_dev(q)->name : "(null)"    )
>                 __string(       kind,           q->ops->id              )
>                 __field(        u32,            parent                  )
>                 __field(        u32,            handle                  )
>         ),

It looks better to align the name with the current convention.

Link:
https://lore.kernel.org/linux-trace-kernel/20240222211442.634192653@goodmis.org/

>         TP_fast_assign(
> -               __assign_str(dev, qdisc_dev(q)->name);
> +               __assign_str(dev, qdisc_dev(q) ? qdisc_dev(q)->name :
> "(null)");
>                 __assign_str(kind, q->ops->id);
>                 __entry->parent = q->parent;
>                 __entry->handle = q->handle;
> 
> 

The second part you mentioned, Steve recently worked on it and changed it.

Link:
https://lore.kernel.org/linux-trace-kernel/20240516133454.681ba6a0@rorschach.local.home/

If it hadn't, I don't think I would have been able to prevent the panic
by just applying my patch.

Link:
https://lore.kernel.org/all/e2f9da4e-919d-4a98-919d-167726ef6bc7@gmail.com/

Warm Regards,
Yunseong Kim