linux-kernel - Re: [PATCH] libbpf: Initialize st

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Message-ID: <CAOpe7ScEK4PZ=43QhMSeJnh4PpJ67T1R5m45pFhkeD3EiQzUKQ@mail.gmail.com>
Date: Wed, 21 Aug 2024 19:53:06 +0900
From: Soma Nakata <soma.nakata01@...il.com>
To: Christophe JAILLET <christophe.jaillet@...adoo.fr>
Cc: Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, 
	Andrii Nakryiko <andrii@...nel.org>, Martin KaFai Lau <martin.lau@...ux.dev>, 
	Eduard Zingerman <eddyz87@...il.com>, Song Liu <song@...nel.org>, 
	Yonghong Song <yonghong.song@...ux.dev>, John Fastabend <john.fastabend@...il.com>, 
	KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>, 
	Jiri Olsa <jolsa@...nel.org>, bpf@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] libbpf: Initialize st_ops->tname with strdup()

`type` field is supposed to directly point to the btf in functions
like `btf_members()`. So I will make change only to `tname` field
in this patch.

On Wed, Aug 21, 2024 at 6:04 PM Soma Nakata <soma.nakata01@...il.com> wrote:
>
> Hi,
>
> You're correct, I should add a NULL check.
>
> zfree(&map->st_ops->tname) causes error because tname has
> `const` qualifier.
> Also, I found st_ops->type has the same issue.
> Therefore, I propose removing `const` from `tname` and `type`
> fields of `struct bpf_struct_ops`, and duplicating them from btf.
>
> >
> > Le 21/08/2024 à 08:46, Soma Nakata a écrit :
> > > `tname` is returned by `btf__name_by_offset()` as well as `var_name`,
> > > and these addresses point to strings in the btf. Since their locations
> > > may change while loading the bpf program, using `strdup()` ensures
> > > `tname` is safely stored.
> > >
> > > Signed-off-by: Soma Nakata <soma.nakata01@...il.com>
> > > ---
> > >   tools/lib/bpf/libbpf.c | 2 +-
> > >   1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> > > index a3be6f8fac09..ece1f1af2cd4 100644
> > > --- a/tools/lib/bpf/libbpf.c
> > > +++ b/tools/lib/bpf/libbpf.c
> > > @@ -1423,7 +1423,7 @@ static int init_struct_ops_maps(struct bpf_object *obj, const char *sec_name,
> > >               memcpy(st_ops->data,
> > >                      data->d_buf + vsi->offset,
> > >                      type->size);
> > > -             st_ops->tname = tname;
> > > +             st_ops->tname = strdup(tname);
> >
> > Hi,
> >
> > Should a NULL check be added (as done a few lines above for the
> > [cm]alloc()) and bpf_map__destroy() updated with a
> > zfree(&map->st_ops->tname) ?
> >
> > CJ
> >
> > >               st_ops->type = type;
> > >               st_ops->type_id = type_id;
> > >
> >