Re: [PATCH] libbpf: fix possible NULL pointer dereference when destroy skelton

From: Andrii Nakryiko <andrii.nakryiko@gmail.com>
To: Yafang Shao <laoar.shao@gmail.com>
Cc: Daniel Borkmann <daniel@iogearbox.net>,
	Alexei Starovoitov <ast@kernel.org>,
	Andrii Nakryiko <andrii@kernel.org>, Martin Lau <kafai@fb.com>,
	Song Liu <songliubraving@fb.com>, Yonghong Song <yhs@fb.com>,
	john fastabend <john.fastabend@gmail.com>,
	KP Singh <kpsingh@kernel.org>,
	Networking <netdev@vger.kernel.org>, bpf <bpf@vger.kernel.org>
Subject: Re: [PATCH] libbpf: fix possible NULL pointer dereference when destroy skelton
Date: Sun, 9 Jan 2022 17:48:39 -0800	[thread overview]
Message-ID: <CAEf4BzZe7_VDOKBiDpD3gn5XVAfkpOVUyowyTo_ziqDuhFTqyQ@mail.gmail.com> (raw)
In-Reply-To: <20220108134739.32541-1-laoar.shao@gmail.com>

On Sat, Jan 8, 2022 at 5:47 AM Yafang Shao <laoar.shao@gmail.com> wrote:
>
> When I checked the code in skelton header file generated with my own bpf
> prog, I found there may be possible NULL pointer derefence when destroy
> skelton. Then I checked the in-tree bpf progs, finding that is a common
> issue. Let's take the generated samples/bpf/xdp_redirect_cpu.skel.h for
> example. Below is the generated code in
> xdp_redirect_cpu__create_skeleton(),
>         xdp_redirect_cpu__create_skeleton
>                 struct bpf_object_skeleton *s;
>                 s = (struct bpf_object_skeleton *)calloc(1, sizeof(*s));
>                 if (!s)
>                         goto error;
>                 ...
>         error:
>                 bpf_object__destroy_skeleton(s);
>                 return  -ENOMEM;
>
> After goto error, the NULL 's' will be deferenced in
> bpf_object__destroy_skeleton().
>
> We can simply fix this issue by just adding a NULL check in
> bpf_object__destroy_skeleton().
>
> Fixes: d66562fba ("libbpf: Add BPF object skeleton support")

We ask to use 12-character short SHA, I've fixed it up, but for future
submissions keep this in mind.

Fixed a few typos and applied to bpf-next, thanks.

> Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
> Cc: Andrii Nakryiko <andrii@kernel.org>
> ---
>  tools/lib/bpf/libbpf.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 7c74342bb668..a07fbd59e4b8 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -11464,6 +11464,9 @@ void bpf_object__detach_skeleton(struct bpf_object_skeleton *s)
>
>  void bpf_object__destroy_skeleton(struct bpf_object_skeleton *s)
>  {
> +       if (!s)
> +               return;
> +
>         if (s->progs)
>                 bpf_object__detach_skeleton(s);
>         if (s->obj)
> --
> 2.17.1
>