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From:   Denis Kirjanov <kda@linux-powerpc.org>
Date:   Tue, 10 Nov 2020 16:02:27 +0300
Message-ID: <CAOJe8K2tL5x-dESsV+PFq1Gii-yB=fJh7i-=E-FbrJeioo6pqA@mail.gmail.com>
Subject: Re: [PATCH] bpf: Fix unsigned 'datasec_id' compared with zero in check_pseudo_btf_id
To:     xiakaixu1987@gmail.com
Cc:     ast@kernel.org, daniel@iogearbox.net, kafai@fb.com,
        songliubraving@fb.com, yhs@fb.com, andrii@kernel.org,
        john.fastabend@gmail.com, kpsingh@chromium.org,
        netdev@vger.kernel.org, bpf@vger.kernel.org,
        linux-kernel@vger.kernel.org, Kaixu Xia <kaixuxia@tencent.com>
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On 11/10/20, xiakaixu1987@gmail.com <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;

but the value is passed as u32 to btf_type_by_id()...

btf_find_by_name_kind() returns s32


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