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From:   Andrii Nakryiko <andrii.nakryiko@gmail.com>
Date:   Tue, 10 Nov 2020 10:41:10 -0800
Message-ID: <CAEf4BzbUW+rzk1KE3---j3d2-YD_HOxKLNUPW=_AL63Qn5pHkg@mail.gmail.com>
Subject: Re: [PATCH] bpf: Fix unsigned 'datasec_id' compared with zero in check_pseudo_btf_id
To:     xiakaixu1987@gmail.com
Cc:     Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Martin Lau <kafai@fb.com>, Song Liu <songliubraving@fb.com>,
        Yonghong Song <yhs@fb.com>,
        Andrii Nakryiko <andrii@kernel.org>,
        john fastabend <john.fastabend@gmail.com>,
        KP Singh <kpsingh@chromium.org>,
        Networking <netdev@vger.kernel.org>, bpf <bpf@vger.kernel.org>,
        open list <linux-kernel@vger.kernel.org>,
        Kaixu Xia <kaixuxia@tencent.com>
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On Tue, Nov 10, 2020 at 3:50 AM <xiakaixu1987@gmail.com> wrote:
>
> From: Kaixu Xia <kaixuxia@tencent.com>
>
> The unsigned variable datasec_id is assigned a return value from the call
> to check_pseudo_btf_id(), which may return negative error code.
>
> Fixes coccicheck warning:
>
> ./kernel/bpf/verifier.c:9616:5-15: WARNING: Unsigned expression compared with zero: datasec_id > 0
>
> Reported-by: Tosk Robot <tencent_os_robot@tencent.com>
> Signed-off-by: Kaixu Xia <kaixuxia@tencent.com>
> ---
>  kernel/bpf/verifier.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 6200519582a6..e9d8d4309bb4 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -9572,7 +9572,7 @@ static int check_pseudo_btf_id(struct bpf_verifier_env *env,
>                                struct bpf_insn *insn,
>                                struct bpf_insn_aux_data *aux)
>  {
> -       u32 datasec_id, type, id = insn->imm;
> +       s32 datasec_id, type, id = insn->imm;

you are changing types for type and id variables here, so split out
datasec_id definition into a separate line

>         const struct btf_var_secinfo *vsi;
>         const struct btf_type *datasec;
>         const struct btf_type *t;
> --
> 2.20.0
>