netdev - Re: [PATCH bpf] libbpf: fix erroneous multi-closing of BTF FD

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Message-ID: <CAADnVQK4mj7bwTQyJu34J=xU3rz7FrXg0Px+xin+Ab5W6AvYDw@mail.gmail.com>
Date:   Fri, 26 Jul 2019 17:24:32 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Andrii Nakryiko <andriin@...com>
Cc:     bpf <bpf@...r.kernel.org>,
        Network Development <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrey Ignatov <rdna@...com>, Yonghong Song <yhs@...com>,
        Andrii Nakryiko <andrii.nakryiko@...il.com>,
        Kernel Team <kernel-team@...com>
Subject: Re: [PATCH bpf] libbpf: fix erroneous multi-closing of BTF FD

On Fri, Jul 26, 2019 at 2:25 PM Andrii Nakryiko <andriin@...com> wrote:
>
> Libbpf stores associated BTF FD per each instance of bpf_program. When
> program is unloaded, that FD is closed. This is wrong, because leads to
> a race and possibly closing of unrelated files, if application
> simultaneously opens new files while bpf_programs are unloaded.
>
> It's also unnecessary, because struct btf "owns" that FD, and
> btf__free(), called from bpf_object__close() will close it. Thus the fix
> is to never have per-program BTF FD and fetch it from obj->btf, when
> necessary.
>
> Fixes: 2993e0515bb4 ("tools/bpf: add support to read .BTF.ext sections")
> Reported-by: Andrey Ignatov <rdna@...com>
> Signed-off-by: Andrii Nakryiko <andriin@...com>

Applied. Thanks