linux-kernel - Re: [PATCH bpf-next] bpftool: Check map name length when map create

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Message-ID: <3da61b9b-fa44-4a45-bccb-40a23ef997ce@kernel.org>
Date: Tue, 11 Feb 2025 10:20:27 +0000
From: Quentin Monnet <qmo@...nel.org>
To: Rong Tao <rtoax@...mail.com>, ast@...nel.org, daniel@...earbox.net
Cc: rongtao@...tc.cn, Andrii Nakryiko <andrii@...nel.org>,
 Martin KaFai Lau <martin.lau@...ux.dev>, Eduard Zingerman
 <eddyz87@...il.com>, 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>,
 "open list:BPF [TOOLING] (bpftool)" <bpf@...r.kernel.org>,
 open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH bpf-next] bpftool: Check map name length when map create

2025-02-11 16:45 UTC+0800 ~ Rong Tao <rtoax@...mail.com>
> From: Rong Tao <rongtao@...tc.cn>
> 
> The size of struct bpf_map::name is BPF_OBJ_NAME_LEN (16).
> 
> bpf(2) {
>   map_create() {
>     bpf_obj_name_cpy(map->name, attr->map_name, sizeof(attr->map_name));
>   }
> }
> 
> When specifying a map name using bpftool map create name, no error is
> reported if the name length is greater than 15.
> 
>     $ sudo bpftool map create /sys/fs/bpf/12345678901234567890 \
>         type array key 4 value 4 entries 5 name 12345678901234567890
> 
> Users will think that 12345678901234567890 is legal, but this name cannot
> be used to index a map.
> 
>     $ sudo bpftool map show name 12345678901234567890
>     Error: can't parse name
> 
>     $ sudo bpftool map show
>     ...
>     1249: array  name 123456789012345  flags 0x0
>     	key 4B  value 4B  max_entries 5  memlock 304B
> 
>     $ sudo bpftool map show name 123456789012345
>     1249: array  name 123456789012345  flags 0x0
>     	key 4B  value 4B  max_entries 5  memlock 304B
> 
> The map name provided in the command line is truncated, but no error is
> reported. This submission checks the length of the map name.
> 
> Signed-off-by: Rong Tao <rongtao@...tc.cn>
> ---
>  tools/bpf/bpftool/map.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/tools/bpf/bpftool/map.c b/tools/bpf/bpftool/map.c
> index ed4a9bd82931..fa00f7865065 100644
> --- a/tools/bpf/bpftool/map.c
> +++ b/tools/bpf/bpftool/map.c
> @@ -1330,6 +1330,12 @@ static int do_create(int argc, char **argv)
>  		goto exit;
>  	}
>  
> +	if (strlen(map_name) > BPF_OBJ_NAME_LEN - 1) {
> +		p_err("The map name is too long, should be less than %d\n",


Nit: I'd drop "The" (and the capital letter) for consistency with other
messages in bpftool; and I'd replace "less than ..." with "no longer
than %d characters\n" to make it explicit and avoid confusion between
"strictly less" and "less or equal".


> +		      BPF_OBJ_NAME_LEN - 1);
> +		goto exit;
> +	}
> +
>  	set_max_rlimit();
>  
>  	fd = bpf_map_create(map_type, map_name, key_size, value_size, max_entries, &attr);


There's no need to defer the check until after we've parsed all
arguments. Can you move it to the location where we retrieve the name,
please?:

		[...]
		} else if (is_prefix(*argv, "name")) {
			NEXT_ARG();
			map_name = GET_ARG();
		} else ...

pw-bot: cr

Apart from these, it's a good idea to fix it, thank you!
Quentin