Re: [PATCH] bpf: Remove unused field initialization

[Stanislav Fomichev]

On Wed, Dec 21, 2022 at 11:55 AM Ricardo Ribalda <ribalda@xxxxxxxxxxxx> 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);

Maybe we should really do the following instead?

.maxlen: sizeof(int)

?

> Signed-off-by: Ricardo Ribalda <ribalda@xxxxxxxxxxxx>
> ---
> 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@xxxxxxxxxx>
> To: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
> To: John Fastabend <john.fastabend@xxxxxxxxx>
> To: Andrii Nakryiko <andrii@xxxxxxxxxx>
> To: Martin KaFai Lau <martin.lau@xxxxxxxxx>
> To: Song Liu <song@xxxxxxxxxx>
> To: Yonghong Song <yhs@xxxxxx>
> To: KP Singh <kpsingh@xxxxxxxxxx>
> To: Stanislav Fomichev <sdf@xxxxxxxxxx>
> To: Hao Luo <haoluo@xxxxxxxxxx>
> To: Jiri Olsa <jolsa@xxxxxxxxxx>
> Cc: bpf@xxxxxxxxxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> ---
>  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@xxxxxxxxxxxx>