linux-kernel - Re: [PATCH] libbpf: check the btf

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Message-ID: <57d88cd3-3cbc-4d30-be82-92990a7a50fd@linux.dev>
Date: Tue, 6 Aug 2024 10:38:14 -0700
From: Yonghong Song <yonghong.song@...ux.dev>
To: Ma Ke <make24@...as.ac.cn>, andrii@...nel.org, eddyz87@...il.com,
 ast@...nel.org, daniel@...earbox.net, martin.lau@...ux.dev, song@...nel.org,
 john.fastabend@...il.com, kpsingh@...nel.org, sdf@...ichev.me,
 haoluo@...gle.com, jolsa@...nel.org, delyank@...com
Cc: bpf@...r.kernel.org, linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH] libbpf: check the btf_type kind to prevent error


On 8/6/24 3:51 AM, Ma Ke wrote:
> To prevent potential error return values, it is necessary to check the
> return value of btf__type_by_id. We can add a kind checking to fix the
> issue.
>
> Cc: stable@...r.kernel.org
> Fixes: 430025e5dca5 ("libbpf: Add subskeleton scaffolding")
> Signed-off-by: Ma Ke <make24@...as.ac.cn>
> ---
>   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 a3be6f8fac09..d1eb45d16054 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -13850,6 +13850,9 @@ int bpf_object__open_subskeleton(struct bpf_object_subskeleton *s)
>   		var = btf_var_secinfos(map_type);
>   		for (i = 0; i < len; i++, var++) {
>   			var_type = btf__type_by_id(btf, var->type);
> +			if (!var_type)
> +				return libbpf_err(-ENOENT);

Could you give a detailed example when this error could be triggered?

> +
>   			var_name = btf__name_by_offset(btf, var_type->name_off);
>   			if (strcmp(var_name, var_skel->name) == 0) {
>   				*var_skel->addr = map->mmaped + var->offset;