netdev - Re: [PATCH v2 bpf-next 10/17] libbpf: tighten BTF type ID rewriting with error checking

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Date:   Thu, 22 Apr 2021 09:50:25 -0700
From:   Yonghong Song <yhs@...com>
To:     Andrii Nakryiko <andrii@...nel.org>, <bpf@...r.kernel.org>,
        <netdev@...r.kernel.org>, <ast@...com>, <daniel@...earbox.net>
CC:     <kernel-team@...com>
Subject: Re: [PATCH v2 bpf-next 10/17] libbpf: tighten BTF type ID rewriting
 with error checking



On 4/16/21 1:23 PM, Andrii Nakryiko wrote:
> It should never fail, but if it does, it's better to know about this rather
> than end up with nonsensical type IDs.

So this is defensive programming. Maybe do another round of
audit of the callers and if you didn't find any issue, you
do not need to check not-happening condition here?

> 
> Signed-off-by: Andrii Nakryiko <andrii@...nel.org>
> ---
>   tools/lib/bpf/linker.c | 9 +++++++++
>   1 file changed, 9 insertions(+)
> 
> diff --git a/tools/lib/bpf/linker.c b/tools/lib/bpf/linker.c
> index 283249df9831..d5dc1d401f57 100644
> --- a/tools/lib/bpf/linker.c
> +++ b/tools/lib/bpf/linker.c
> @@ -1423,6 +1423,15 @@ static int linker_fixup_btf(struct src_obj *obj)
>   static int remap_type_id(__u32 *type_id, void *ctx)
>   {
>   	int *id_map = ctx;
> +	int new_id = id_map[*type_id];
> +
> +	if (*type_id == 0)
> +		return 0;
> +
> +	if (new_id == 0) {
> +		pr_warn("failed to find new ID mapping for original BTF type ID %u\n", *type_id);
> +		return -EINVAL;
> +	}
>   
>   	*type_id = id_map[*type_id];
>   
>