Re: [Intel-wired-lan] [PATCH v1] igc: Fix kernel NULL pointer dereference

[Kurt Kanzenbach <kurt@linutronix.de>]

[-- Attachment #1.1: Type: text/plain, Size: 2034 bytes --]

On Wed Sep 14 2022, Zulkifli, Muhammad Husaini wrote:
> Hi Vinicius,
>
> Thanks for the review. Replied inline
>
>> -----Original Message-----
>> From: Gomes, Vinicius <vinicius.gomes@intel.com>
>> Sent: Thursday, 15 September, 2022 3:04 AM
>> To: Zulkifli, Muhammad Husaini <muhammad.husaini.zulkifli@intel.com>;
>> intel-wired-lan@osuosl.org
>> Cc: Zulkifli, Muhammad Husaini <muhammad.husaini.zulkifli@intel.com>
>> Subject: Re: [Intel-wired-lan] [PATCH v1] igc: Fix kernel NULL pointer
>> dereference
>> 
>> Hi Husaini,
>> 
>> Muhammad Husaini Zulkifli <muhammad.husaini.zulkifli@intel.com> writes:
>> 
>> > This patch fix the null pointer dereference when dereference the
>> > pointer that is expected to be valid but is NULL, typically will cause
>> > kernel crash as below:
>> >
>> 
>> This part of the message only repeats that you found NULL dereference
>> related crash, which is already clear from the splat below.
>> 
>> Can you give more details about how you manage to crash? What is schedule
>> that you tried to use, that kind of thing. Perhaps the problem is somewhere
>> else and we are only hiding the problem.
>
> With below schedule, if you are not try to dereferencing the pointer, we cannot catch this. 
> Might be compiler already handle it. This is a guard to ensure that "prev" pointer always valid
> Address before using it. It will always NULL if you have 1 GCL schedule entry.

Hm. Yes, prev is NULL for the first schedule entry. Nevertheless, it
shouldn't be referenced, as `queue_uses[i] > 1' cannot be true for the
first entry unless I'm missing something.

>
>    Example schedule:
>
>     tc qdisc replace dev ${INTERFACE} handle 100 parent root taprio num_tc 3 \
>        map 2 2 1 0 2 2 2 2 2 2 2 2 2 2 2 2 \
>        queues 1@0 1@1 2@2 \
>        base-time ${BASETIME} \
>        sched-entry S 0x01 300000 
>        flags 0x02

Well, with this schedule I cannot reproduce the issue. What kernel
version are you testing? Mainline?

Thanks,
Kurt

[-- Attachment #1.2: signature.asc --]
[-- Type: application/pgp-signature, Size: 861 bytes --]

[-- Attachment #2: Type: text/plain, Size: 162 bytes --]

_______________________________________________
Intel-wired-lan mailing list
Intel-wired-lan@osuosl.org
https://lists.osuosl.org/mailman/listinfo/intel-wired-lan