linux-kernel - Re: [PATCH bpf-next v2 2/6] bpf: Add a ARG_PTR_TO_CONST

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Message-ID: <CABRcYmKUQcRjQhLgpM6pb4oMWCB2=ov8iL1prxn3B54Or=aC=w@mail.gmail.com>
Date:   Tue, 6 Apr 2021 17:38:31 +0200
From:   Florent Revest <revest@...omium.org>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc:     bpf <bpf@...r.kernel.org>, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Yonghong Song <yhs@...com>, KP Singh <kpsingh@...nel.org>,
        Brendan Jackman <jackmanb@...omium.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH bpf-next v2 2/6] bpf: Add a ARG_PTR_TO_CONST_STR argument type

On Fri, Mar 26, 2021 at 11:23 PM Andrii Nakryiko
<andrii.nakryiko@...il.com> wrote:
> On Tue, Mar 23, 2021 at 7:23 PM Florent Revest <revest@...omium.org> wrote:
> > +
> > +               map_off = reg->off + reg->var_off.value;
> > +               err = map->ops->map_direct_value_addr(map, &map_addr, map_off);
> > +               if (err)
> > +                       return err;
> > +
> > +               str_ptr = (char *)(long)(map_addr);
> > +               if (!strnchr(str_ptr + map_off,
> > +                            map->value_size - reg->off - map_off, 0))
>
> you are double subtracting reg->off here. isn't map->value_size -
> map_off what you want?

Good catch!

> > +                       verbose(env, "string is not zero-terminated\n");
>
> I'd prefer `return -EINVAL;`, but at least set err, otherwise what's the point?

Ah yeah, absolutely.