linux-kernel - Re: [PATCH v2] libbpf: Initialize st

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Message-ID: <ecd1af32-8e6b-45d3-8434-0e981fd198ea@wanadoo.fr>
Date: Wed, 21 Aug 2024 14:15:59 +0200
From: Christophe JAILLET <christophe.jaillet@...adoo.fr>
To: Soma Nakata <soma.nakata01@...il.com>, Andrii Nakryiko
 <andrii@...nel.org>, Eduard Zingerman <eddyz87@...il.com>,
 Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>,
 Martin KaFai Lau <martin.lau@...ux.dev>, Song Liu <song@...nel.org>,
 Yonghong Song <yonghong.song@...ux.dev>,
 John Fastabend <john.fastabend@...il.com>, KP Singh <kpsingh@...nel.org>,
 Stanislav Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>,
 Jiri Olsa <jolsa@...nel.org>
Cc: bpf@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] libbpf: Initialize st_ops->tname with strdup()

Le 21/08/2024 à 13:23, Soma Nakata a écrit :
> `tname` is returned by `btf__name_by_offset()` as well as `var_name`,
> and these addresses point to strings in the btf. Since their locations
> may change while loading the bpf program, using `strdup()` ensures
> `tname` is safely stored.
> 
> Signed-off-by: Soma Nakata <soma.nakata01@...il.com>
> ---
>   tools/lib/bpf/libbpf.c | 7 +++++--
>   1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index a3be6f8fac09..f4ad1b993ec5 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -496,7 +496,7 @@ struct bpf_program {
>   };
>   
>   struct bpf_struct_ops {
> -	const char *tname;
> +	char *tname;
>   	const struct btf_type *type;
>   	struct bpf_program **progs;
>   	__u32 *kern_func_off;
> @@ -1423,7 +1423,9 @@ static int init_struct_ops_maps(struct bpf_object *obj, const char *sec_name,
>   		memcpy(st_ops->data,
>   		       data->d_buf + vsi->offset,
>   		       type->size);
> -		st_ops->tname = tname;
> +		st_ops->tname = strdup(tname);
> +		if (!st_ops->tname)
> +			return -ENOMEM;

Certainly a matter of taste, but I would personally move it just after 
"st_ops->kern_func_off = malloc()" and add the NULL check with the 
existing ones.

BTW, there are some memory leaks if 1 or more allocations fail in this 
function.
Not sure if it is an issue or not, and what should be done in this case.

CJ


>   		st_ops->type = type;
>   		st_ops->type_id = type_id;
>   
> @@ -8984,6 +8986,7 @@ static void bpf_map__destroy(struct bpf_map *map)
>   	map->mmaped = NULL;
>   
>   	if (map->st_ops) {
> +		zfree(&map->st_ops->tname);
>   		zfree(&map->st_ops->data);
>   		zfree(&map->st_ops->progs);
>   		zfree(&map->st_ops->kern_func_off);