linux-kernel - Re: [PATCH bpf-next v2] libbpf: Fix strncat bounds error in libbpf_prog_type_by

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Date:   Wed, 23 Oct 2019 21:37:27 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     KP Singh <kpsingh@...omium.org>
Cc:     open list <linux-kernel@...r.kernel.org>,
        bpf <bpf@...r.kernel.org>, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        Florent Revest <revest@...omium.org>
Subject: Re: [PATCH bpf-next v2] libbpf: Fix strncat bounds error in libbpf_prog_type_by_name

On Wed, Oct 23, 2019 at 9:06 PM KP Singh <kpsingh@...omium.org> wrote:
>
> From: KP Singh <kpsingh@...gle.com>
>
> On compiling samples with this change, one gets an error:
>
>  error: ‘strncat’ specified bound 118 equals destination size
>   [-Werror=stringop-truncation]
>
>     strncat(dst, name + section_names[i].len,
>     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>      sizeof(raw_tp_btf_name) - (dst - raw_tp_btf_name));
>      ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> strncat requires the destination to have enough space for the
> terminating null byte.
>
> Fixes: f75a697e09137 ("libbpf: Auto-detect btf_id of BTF-based raw_tracepoint")
> Signed-off-by: KP Singh <kpsingh@...gle.com>
> ---

Acked-by: Andrii Nakryiko <andriin@...com>

>  tools/lib/bpf/libbpf.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 290684b504b7..dc7d493a7d3d 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -4693,7 +4693,7 @@ int libbpf_prog_type_by_name(const char *name, enum bpf_prog_type *prog_type,
>                         }
>                         /* prepend "btf_trace_" prefix per kernel convention */
>                         strncat(dst, name + section_names[i].len,
> -                               sizeof(raw_tp_btf_name) - (dst - raw_tp_btf_name));
> +                               sizeof(raw_tp_btf_name) - sizeof("btf_trace_"));
>                         ret = btf__find_by_name(btf, raw_tp_btf_name);
>                         btf__free(btf);
>                         if (ret <= 0) {
> --
> 2.20.1
>