netdev - Re: [PATCH bpf] libbpf: always NULL out pobj in bpf_prog_load

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Message-ID: <CACAyw9-HMaFh3it_nPs96+tdthbhzV+cjEfFNT_G20ghKCwfvQ@mail.gmail.com>
Date:   Tue, 7 May 2019 10:09:12 +0100
From:   Lorenz Bauer <lmb@...udflare.com>
To:     Martin Lau <kafai@...com>
Cc:     "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "ast@...nel.org" <ast@...nel.org>,
        "daniel@...earbox.net" <daniel@...earbox.net>
Subject: Re: [PATCH bpf] libbpf: always NULL out pobj in bpf_prog_load_xattr

On Thu, 2 May 2019 at 17:03, Martin Lau <kafai@...com> wrote:
>
> On Thu, May 02, 2019 at 11:49:32AM -0400, Lorenz Bauer wrote:
> > Currently, code like the following segfaults if bpf_prog_load_xattr
> > returns an error:
> >
> >     struct bpf_object *obj;
> >
> >     err = bpf_prog_load_xattr(&attr, &obj, &prog_fd);
> >     bpf_object__close(obj);
> This is a bug.  err should always be checked first before
> using obj or prog_fd.  If there is err, calling bpf_object__close(NULL)
> is another redundancy.

Ack, I'll send another patch. The bug is in a couple of places, so I
figured that this is something people do naturally.

>
> >     if (err)
> >         ...
> >
> > Unconditionally reset pobj to NULL at the start of the function
> > to fix this.
> Hence, this change is unnecessary.
>
> >
> > Signed-off-by: Lorenz Bauer <lmb@...udflare.com>
> > ---
> >  tools/lib/bpf/libbpf.c | 2 ++
> >  1 file changed, 2 insertions(+)
> >
> > diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> > index 11a65db4b93f..2ddf3212b8f7 100644
> > --- a/tools/lib/bpf/libbpf.c
> > +++ b/tools/lib/bpf/libbpf.c
> > @@ -3363,6 +3363,8 @@ int bpf_prog_load_xattr(const struct bpf_prog_load_attr *attr,
> >       struct bpf_map *map;
> >       int err;
> >
> > +     *pobj = NULL;
> > +
> >       if (!attr)
> >               return -EINVAL;
> >       if (!attr->file)
> > --
> > 2.19.1
> >



-- 
Lorenz Bauer  |  Systems Engineer
25 Lavington St., London SE1 0NZ

www.cloudflare.com