Re: [PATCH bpf-next v2] bpftool: Remove BPF_OBJ_NAME_LEN restriction when looking up bpf program by name

[Quentin Monnet <quentin@isovalent.com>]

On 31/07/2022 19:10, Manu Bretelle wrote:
> bpftool was limiting the length of names to BPF_OBJ_NAME_LEN in prog_parse
> fds.
> 
> Since commit b662000aff84 ("bpftool: Adding support for BTF program names")
> we can get the full program name from BTF.
> 
> This patch removes the restriction of name length when running `bpftool
> prog show name ${name}`.
> 
> Test:
> Tested against some internal program names that were longer than
> `BPF_OBJ_NAME_LEN`, here a redacted example of what was ran to test.
> 
>     # previous behaviour
>     $ sudo bpftool prog show name some_long_program_name
>     Error: can't parse name
>     # with the patch
>     $ sudo ./bpftool prog show name some_long_program_name
>     123456789: tracing  name some_long_program_name  tag taghexa  gpl ....
>     ...
>     ...
>     ...
>     # too long
>     sudo ./bpftool prog show name $(python3 -c 'print("A"*128)')
>     Error: can't parse name
>     # not too long but no match
>     $ sudo ./bpftool prog show name $(python3 -c 'print("A"*127)')
> 
> Signed-off-by: Manu Bretelle <chantr4@gmail.com>
> 
> ---
> 
> v1 -> v2:
> * Fix commit message to follow patch submission guidelines
> * use strncmp instead of strcmp
> * reintroduce arg length check against MAX_PROG_FULL_NAME
> 
> 
>  tools/bpf/bpftool/common.c | 15 ++++++++++++---
>  1 file changed, 12 insertions(+), 3 deletions(-)
> 
> diff --git a/tools/bpf/bpftool/common.c b/tools/bpf/bpftool/common.c
> index 067e9ea59e3b..3ea747b3b194 100644
> --- a/tools/bpf/bpftool/common.c
> +++ b/tools/bpf/bpftool/common.c
> @@ -722,6 +722,7 @@ print_all_levels(__maybe_unused enum libbpf_print_level level,
>  
>  static int prog_fd_by_nametag(void *nametag, int **fds, bool tag)
>  {
> +	char prog_name[MAX_PROG_FULL_NAME];
>  	unsigned int id = 0;
>  	int fd, nb_fds = 0;
>  	void *tmp;
> @@ -754,12 +755,20 @@ static int prog_fd_by_nametag(void *nametag, int **fds, bool tag)
>  			goto err_close_fd;
>  		}
>  
> -		if ((tag && memcmp(nametag, info.tag, BPF_TAG_SIZE)) ||
> -		    (!tag && strncmp(nametag, info.name, BPF_OBJ_NAME_LEN))) {
> +		if (tag && memcmp(nametag, info.tag, BPF_TAG_SIZE)) {
>  			close(fd);
>  			continue;
>  		}
>  
> +		if (!tag) {
> +			get_prog_full_name(&info, fd, prog_name,
> +				sizeof(prog_name));

Nit: This line should be aligned with the opening parenthesis from the
line above, checkpatch.pl complains about it. Probably not worth sending
a new version just for that, though.

> +			if (strncmp(nametag, prog_name, sizeof(prog_name))) {
> +				close(fd);
> +				continue;
> +			}
> +		}
> +
>  		if (nb_fds > 0) {
>  			tmp = realloc(*fds, (nb_fds + 1) * sizeof(int));
>  			if (!tmp) {
> @@ -820,7 +829,7 @@ int prog_parse_fds(int *argc, char ***argv, int **fds)
>  		NEXT_ARGP();
>  
>  		name = **argv;
> -		if (strlen(name) > BPF_OBJ_NAME_LEN - 1) {
> +		if (strlen(name) > MAX_PROG_FULL_NAME - 1) {
>  			p_err("can't parse name");
>  			return -1;
>  		}

Looks good, thank you!

Reviewed-by: Quentin Monnet <quentin@isovalent.com>