netdev - Re: [PATCH bpf] tools/bpf: only set obj->skeleton without err

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Date:   Sun, 9 Jan 2022 18:04:45 -0800
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Wei Fu <fuweid89@...il.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>, Martin Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        john fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>, bpf <bpf@...r.kernel.org>,
        Networking <netdev@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH bpf] tools/bpf: only set obj->skeleton without err

On Sat, Jan 8, 2022 at 12:40 AM Wei Fu <fuweid89@...il.com> wrote:
>
> After `bpftool gen skeleton`, the ${bpf_app}.skel.h will provide that
> ${bpf_app_name}__open helper to load bpf. If there is some error
> like ENOMEM, the ${bpf_app_name}__open will rollback(free) the allocated
> object, including `bpf_object_skeleton`.
>
> Since the ${bpf_app_name}__create_skeleton set the obj->skeleton first
> and not rollback it when error, it will cause double-free in
> ${bpf_app_name}__destory at ${bpf_app_name}__open. Therefore, we should
> set the obj->skeleton before return 0;
>
> Signed-off-by: Wei Fu <fuweid89@...il.com>
> ---
>  tools/bpf/bpftool/gen.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>

Great catch! Added (please add it yourself in the future):

Fixes: 5dc7a8b21144 ("bpftool, selftests/bpf: Embed object file inside
skeleton")

Also reworded the subject a bit. Pushed to bpf-next.

> diff --git a/tools/bpf/bpftool/gen.c b/tools/bpf/bpftool/gen.c
> index 5c18351290f0..e61e08f524da 100644
> --- a/tools/bpf/bpftool/gen.c
> +++ b/tools/bpf/bpftool/gen.c
> @@ -928,7 +928,6 @@ static int do_skeleton(int argc, char **argv)
>                         s = (struct bpf_object_skeleton *)calloc(1, sizeof(*s));\n\
>                         if (!s)                                             \n\
>                                 goto err;                                   \n\
> -                       obj->skeleton = s;                                  \n\
>                                                                             \n\
>                         s->sz = sizeof(*s);                                 \n\
>                         s->name = \"%1$s\";                                 \n\
> @@ -1001,6 +1000,8 @@ static int do_skeleton(int argc, char **argv)
>                                                                             \n\
>                         s->data = (void *)%2$s__elf_bytes(&s->data_sz);     \n\
>                                                                             \n\
> +                       obj->skeleton = s;                                  \n\
> +                                                                           \n\
>                         return 0;                                           \n\
>                 err:                                                        \n\
>                         bpf_object__destroy_skeleton(s);                    \n\
> --
> 2.25.1
>