linux-kernel - Re: [PATCH bpf-next] libbpf: Optimized return value in libbpf

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Date:   Mon, 5 Dec 2022 22:10:56 +0100
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Xin Liu <liuxin350@...wei.com>, andrii@...nel.org, ast@...nel.org,
        martin.lau@...ux.dev, song@...nel.org, yhs@...com,
        john.fastabend@...il.com, kpsingh@...nel.org, sdf@...gle.com,
        haoluo@...gle.com, jolsa@...nel.org
Cc:     bpf@...r.kernel.org, linux-kernel@...r.kernel.org,
        yanan@...wei.com, wuchangye@...wei.com, xiesongyang@...wei.com,
        kongweibin2@...wei.com, zhangmingyi5@...wei.com
Subject: Re: [PATCH bpf-next] libbpf: Optimized return value in
 libbpf_strerror when errno is libbpf errno

On 12/3/22 10:37 AM, Xin Liu wrote:
> This is a small improvement in libbpf_strerror. When libbpf_strerror
> is used to obtain the system error description, if the length of the
> buf is insufficient, libbpf_sterror returns ERANGE and sets errno to
> ERANGE.
> 
> However, this processing is not performed when the error code
> customized by libbpf is obtained. Make some minor improvements here,
> return -ERANGE and set errno to ERANGE when buf is not enough for
> custom description.
> 
> Signed-off-by: Xin Liu <liuxin350@...wei.com>
> ---
>   tools/lib/bpf/libbpf_errno.c | 6 ++++++
>   1 file changed, 6 insertions(+)
> 
> diff --git a/tools/lib/bpf/libbpf_errno.c b/tools/lib/bpf/libbpf_errno.c
> index 96f67a772a1b..48ce7d5b5bf9 100644
> --- a/tools/lib/bpf/libbpf_errno.c
> +++ b/tools/lib/bpf/libbpf_errno.c
> @@ -54,10 +54,16 @@ int libbpf_strerror(int err, char *buf, size_t size)
>   
>   	if (err < __LIBBPF_ERRNO__END) {
>   		const char *msg;
> +		size_t msg_size;
>   
>   		msg = libbpf_strerror_table[ERRNO_OFFSET(err)];
>   		snprintf(buf, size, "%s", msg);
>   		buf[size - 1] = '\0';
> +
> +		msg_size = strlen(msg);
> +		if (msg_size >= size)
> +			return libbpf_err(-ERANGE);

Given this is related to libbpf_strerror_table[] where the error strings are known
lets do compile-time error instead. All callers should pass in a buffer of STRERR_BUFSIZE
size in libbpf.

>   		return 0;
>   	}
>   
>