Re: [PATCH bpf-next v3] bpftool: Check map name length when map create

[Quentin Monnet]

2025-02-12 09:20 UTC+0800 ~ Rong Tao <rtoax@xxxxxxxxxxx>
> From: Rong Tao <rongtao@xxxxxxxx>
> 
> 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 warning is
> reported. This submission checks the length of the map name.
> 
> Reviewed-by: Quentin Monnet <qmo@xxxxxxxxxx>
> Signed-off-by: Rong Tao <rongtao@xxxxxxxx>
> ---
> v2: https://lore.kernel.org/lkml/tencent_26592A2BAF08A3A688A50600421559929708@xxxxxx/
> v1: https://lore.kernel.org/lkml/tencent_1C4444032C2188ACD04B4995B0D78F510607@xxxxxx/
> ---
>  tools/bpf/bpftool/map.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/tools/bpf/bpftool/map.c b/tools/bpf/bpftool/map.c
> index ed4a9bd82931..9617e64d3d11 100644
> --- a/tools/bpf/bpftool/map.c
> +++ b/tools/bpf/bpftool/map.c
> @@ -1270,6 +1270,10 @@ static int do_create(int argc, char **argv)
>  		} else if (is_prefix(*argv, "name")) {
>  			NEXT_ARG();
>  			map_name = GET_ARG();
> +			if (strlen(map_name) > BPF_OBJ_NAME_LEN - 1) {
> +				p_info("Warning: map name is longer than %d characters, it will be truncated.\n",


Change looks mostly good, thanks! Two small things to address with this
message string:

- Please remove the trailing '\n', p_info() adds it already.
- Please replace %d with %u. The value is unsigned, and we've merged a
commit to clean these up recently, 17c3dc50294b ("bpftool: Using the
right format specifiers").


> +				      BPF_OBJ_NAME_LEN - 1);
> +			}
>  		} else if (is_prefix(*argv, "key")) {
>  			if (parse_u32_arg(&argc, &argv, &key_size,
>  					  "key size"))