linux-kernel - Re: [PATCH] bpf: Remove unused field initialization

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Date:   Wed, 21 Dec 2022 21:13:12 +0100
From:   Ricardo Ribalda <ribalda@...omium.org>
To:     Stanislav Fomichev <sdf@...gle.com>
Cc:     John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>, Jiri Olsa <jolsa@...nel.org>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Daniel Borkmann <daniel@...earbox.net>,
        Hao Luo <haoluo@...gle.com>, Yonghong Song <yhs@...com>,
        Andrii Nakryiko <andrii@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Song Liu <song@...nel.org>, bpf@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] bpf: Remove unused field initialization

Hi Stanislav

On Wed, 21 Dec 2022 at 21:10, Stanislav Fomichev <sdf@...gle.com> wrote:
>
> On Wed, Dec 21, 2022 at 11:55 AM Ricardo Ribalda <ribalda@...omium.org> wrote:
> >
> > Maxlen is used by standard proc_handlers such as proc_dointvec(), but in this
> > case we have our own proc_handler. Remove the initialization.
>
> Are you sure?
>
> bpf_stats_handler
>   proc_dointvec_minmax
>     do_proc_dointvec
>       __do_proc_dointvec
>         vleft = table->maxlen / sizeof(*i);

I believe do_proc_dointvec is using the value from:

struct ctl_table tmp = {
  .maxlen=sixeof(val);
}

>
> Maybe we should really do the following instead?
>
> .maxlen: sizeof(int)
>
> ?
>
> > Signed-off-by: Ricardo Ribalda <ribalda@...omium.org>
> > ---
> > bpf: Trivial remove of unitialised field.
> >
> > I have inspired myself in your code and heritaded this bug :). Fixing this
> > here so none else makes the same mistake.
> >
> > To: Alexei Starovoitov <ast@...nel.org>
> > To: Daniel Borkmann <daniel@...earbox.net>
> > To: John Fastabend <john.fastabend@...il.com>
> > To: Andrii Nakryiko <andrii@...nel.org>
> > To: Martin KaFai Lau <martin.lau@...ux.dev>
> > To: Song Liu <song@...nel.org>
> > To: Yonghong Song <yhs@...com>
> > To: KP Singh <kpsingh@...nel.org>
> > To: Stanislav Fomichev <sdf@...gle.com>
> > To: Hao Luo <haoluo@...gle.com>
> > To: Jiri Olsa <jolsa@...nel.org>
> > Cc: bpf@...r.kernel.org
> > Cc: linux-kernel@...r.kernel.org
> > ---
> >  kernel/bpf/syscall.c | 1 -
> >  1 file changed, 1 deletion(-)
> >
> > diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> > index 35972afb6850..8e55456bd648 100644
> > --- a/kernel/bpf/syscall.c
> > +++ b/kernel/bpf/syscall.c
> > @@ -5319,7 +5319,6 @@ static struct ctl_table bpf_syscall_table[] = {
> >         {
> >                 .procname       = "bpf_stats_enabled",
> >                 .data           = &bpf_stats_enabled_key.key,
> > -               .maxlen         = sizeof(bpf_stats_enabled_key),
> >                 .mode           = 0644,
> >                 .proc_handler   = bpf_stats_handler,
> >         },
> >
> > ---
> > base-commit: b6bb9676f2165d518b35ba3bea5f1fcfc0d969bf
> > change-id: 20221221-bpf-syscall-58d1ac3f817a
> >
> > Best regards,
> > --
> > Ricardo Ribalda <ribalda@...omium.org>



-- 
Ricardo Ribalda