netdev - Re: [PATCH] xen-netfront: handle NULL returned by xdp_convert_buff_to

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Message-ID: <452bac2e-2840-4db7-bbf4-c41e94d437a8@nppct.ru>
Date: Thu, 17 Apr 2025 11:45:30 +0300
From: Alexey <sdl@...ct.ru>
To: Jürgen Groß <jgross@...e.com>,
 Jakub Kicinski <kuba@...nel.org>
Cc: Stefano Stabellini <sstabellini@...nel.org>,
 Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>,
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Paolo Abeni <pabeni@...hat.com>, Alexei Starovoitov <ast@...nel.org>,
 Daniel Borkmann <daniel@...earbox.net>,
 Jesper Dangaard Brouer <hawk@...nel.org>,
 John Fastabend <john.fastabend@...il.com>, xen-devel@...ts.xenproject.org,
 netdev@...r.kernel.org, linux-kernel@...r.kernel.org, bpf@...r.kernel.org,
 lvc-project@...uxtesting.org, stable@...r.kernel.org
Subject: Re: [PATCH] xen-netfront: handle NULL returned by
 xdp_convert_buff_to_frame()

On 17.04.2025 10:12, Jürgen Groß wrote:
> On 17.04.25 09:00, Alexey wrote:
>>
>> On 17.04.2025 03:58, Jakub Kicinski wrote:
>>> On Mon, 14 Apr 2025 18:34:01 +0000 Alexey Nepomnyashih wrote:
>>>>           get_page(pdata);
>>> Please notice this get_page() here.
>>>
>>>>           xdpf = xdp_convert_buff_to_frame(xdp);
>>>> +        if (unlikely(!xdpf)) {
>>>> +            trace_xdp_exception(queue->info->netdev, prog, act);
>>>> +            break;
>>>> +        }
>> Do you mean that it would be better to move the get_page(pdata) call 
>> lower,
>> after checking for NULL in xdpf, so that the reference count is only 
>> increased
>> after a successful conversion?
>
> I think the error handling here is generally broken (or at least very
> questionable).
>
> I suspect that in case of at least some errors the get_page() is leaking
> even without this new patch.
>
> In case I'm wrong a comment reasoning why there is no leak should be
> added.
>
>
> Juergen

I think pdata is freed in xdp_return_frame_rx_napi() -> __xdp_return()