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

[Rong Tao <rtoax@foxmail.com>]

On 2/11/25 18:20, Quentin Monnet wrote:
> 2025-02-11 16:45 UTC+0800 ~ Rong Tao <rtoax@foxmail.com>
>> From: Rong Tao <rongtao@cestc.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@cestc.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".

Thanks, i'll submit another patch.

Rong Tao.

>
>> +		      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