linux-kernel - Re: tcp: Checking a kmemdup() call in tcp_time

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Message-ID: <CANn89i+WzeMhCysz7QngWM7iMMv1GAuzVez0Gviiud5MZoKO-w@mail.gmail.com>
Date:   Mon, 14 Oct 2019 06:15:48 -0700
From:   Eric Dumazet <edumazet@...gle.com>
To:     Markus Elfring <Markus.Elfring@....de>
Cc:     Eric Dumazet <eric.dumazet@...il.com>,
        netdev <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        Daniel Borkmann <daniel@...earbox.net>,
        "David S. Miller" <davem@...emloft.net>,
        Hideaki Yoshifuji <yoshfuji@...ux-ipv6.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        kernel-janitors@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>,
        Aditya Pakki <pakki001@....edu>, Kangjie Lu <kjlu@....edu>,
        Navid Emamdoost <emamd001@....edu>,
        Stephen McCamant <smccaman@....edu>
Subject: Re: tcp: Checking a kmemdup() call in tcp_time_wait()

On Mon, Oct 14, 2019 at 5:51 AM Markus Elfring <Markus.Elfring@....de> wrote:
>
> >>>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/net/ipv4/tcp_minisocks.c?id=1c0cc5f1ae5ee5a6913704c0d75a6e99604ee30a#n306
> >>>> https://elixir.bootlin.com/linux/v5.4-rc2/source/net/ipv4/tcp_minisocks.c#L306
> …
>
> >> Can an other error reporting approach be nicer here?
> >
> > There is no error reported if kmemdup() has failed.
>
> How do data from the Linux allocation failure report fit to this information?
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/process/coding-style.rst?id=4f5cafb5cb8471e54afdc9054d973535614f7675#n878
>

This is coding style for newly submitted code.

We do not refactor code to the latest coding style, this would cost a lot.

Especially TCP stack that is quite often changed.

>
> > timewait is best effort.
>
> How do you think about to return an error code like “-ENOMEM” at this place?

tcp_time_wait() is void, the caller won't care. I told you time_wait
is best effort.

What is the problem you want to solve _exactly_ ?

Have you seen a real issue, or should you augment your static analyser
to not complain on :

ptr = kmemdup();
BUG_ON(<any condition>);

(<any condition> being different than (ptr == NULL))

I believe we have enough real bugs to fix.
I would prefer to not spend time arguing for every single BUG() or BUG_ON().

Thank you.