netdev - Re: null pointer dereference in interrupt after receiving an ip packet on veth from xsk from user space

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Message-ID: <fbeb5832-0051-4f78-bfdf-f1087bc98510@nop.hu>
Date: Tue, 21 Oct 2025 14:59:48 +0200
From: mc36 <csmate@....hu>
To: Jason Xing <kerneljasonxing@...il.com>,
 Fernando Fernandez Mancera <fmancera@...e.de>
Cc: alekcejk@...glemail.com, Jonathan Lemon <jonathan.lemon@...il.com>,
 Stanislav Fomichev <sdf@...ichev.me>,
 Maciej Fijalkowski <maciej.fijalkowski@...el.com>,
 Magnus Karlsson <magnus.karlsson@...el.com>, Björn Töpel
 <bjorn@...nel.org>, 1118437@...s.debian.org, netdev@...r.kernel.org,
 bpf@...r.kernel.org
Subject: Re: null pointer dereference in interrupt after receiving an ip
 packet on veth from xsk from user space

hi,

you both are crazy good, thank you so much for both of your effort! :)


if you're in a need for some more complicated xsk tests, just let me know, freertr

have a dataplane and a socat-alike tool with an xsk based packetio for a while....

br,

cs

On 10/21/25 14:25, Jason Xing wrote:
> On Tue, Oct 21, 2025 at 6:52   PM Fernando Fernandez Mancera
> <fmancera@...e.de> wrote:
>>
>>
>>
>> On 10/20/25 11:31 PM, mc36 wrote:
>>> hi,
>>>
>>> On 10/20/25 11:04, Jason Xing wrote:
>>>>
>>>> I followed your steps you attached in your code:
>>>> ////// gcc xskInt.c -lxdp
>>>> ////// sudo ip link add veth1 type veth
>>>> ////// sudo ip link set veth0 up
>>>> ////// sudo ip link set veth1 up
>>>
>>> ip link set dev veth1 address 3a:10:5c:53:b3:5c
>>>
>>>> ////// sudo ./a.out
>>>>
>>> that will do the trick on a recent kerlek....
>>>
>>> its the destination mac in the c code....
>>>
>>> ps: chaining in the original reporter from the fedora land.....
>>>
>>>
>>> have a nice day,
>>>
>>> cs
>>>
>>>
>>
>> hi, FWIW I have reproduced this and I bisected it, issue was introduced
>> at 30f241fcf52aaaef7ac16e66530faa11be78a865 - working on a patch.
> 
> Exactly. I simply reverted it and its dependencies and didn't see any
> crash then. It was newly introduced, hopefully it will not bring much
> trouble. As I replied before, I will take a look tomorrow morning.
> 
> Thanks,
> Jason