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

[Quentin Monnet <quentin@isovalent.com>]

On 29/07/2022 07:18, Manu Bretelle wrote:
> From: chantra <chantr4@gmail.com>
> 
> bpftool was limiting the length of names to
> [BPF_OBJ_NAME_LEN](https://github.com/libbpf/bpftool/blob/2d7bba1e8c17dd0422879c856cda66723b209952/src/common.c#L823-L826).
> 
> Since
> https://github.com/libbpf/bpftool/commit/61833a284f48b90f6802c141c8356de64bb41e10
> we can get the full program name from BTF.
> 
> This diffs remove the restriction of name length when running `bpftool

-> "This patch removes"?

> 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.
> 
> ```
> $ sudo bpftool prog show name some_long_program_name
> Error: can't parse name
> $ sudo ./bpftool prog show name some_long_program_name
> 123456789: tracing  name some_long_program_name  tag taghexa  gpl ....
> ...
> ...
> ...
> ```

Thanks a lot for the patch! The suggested change looks good, but the
code and the patch themselves need some adjustments.

Regarding your commit object (and email subject): Please prefix with the
component that you update. For your next version, this should be:

    [PATCH bpf-next v2] bpftool: Remove BPF_OBJ_NAME_LEN...

For the commit description, please avoid external links (GitHub). Prefer
function names (we can grep for them) or commit references [0]. I would
also recommend against too much Markdown mark-up, the triple quotes
could be removed and the snippet indented instead.

Your commit is also missing your Signed-off-by tag in its description,
you will need to add it [1].

[0]
https://www.kernel.org/doc/html/latest/process/submitting-patches.html?highlight=signed+off#describe-your-changes
[1]
https://www.kernel.org/doc/html/latest/process/submitting-patches.html?highlight=signed+off#sign-your-work-the-developer-s-certificate-of-origin

> ---
>  tools/bpf/bpftool/common.c | 18 ++++++++++++------
>  1 file changed, 12 insertions(+), 6 deletions(-)
> 
> diff --git a/tools/bpf/bpftool/common.c b/tools/bpf/bpftool/common.c
> index 067e9ea59e3b..bc9017877296 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 +755,21 @@ 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;
>  		}
>  
> +
> +

Too many blank lines, please use just one.

> +		if (!tag) {
> +			get_prog_full_name(&info, fd, prog_name, sizeof(prog_name));
> +			if (strcmp(nametag, prog_name)) {

strncmp(), please

> +				close(fd);
> +				continue;
> +			}
> +		}
> +
>  		if (nb_fds > 0) {
>  			tmp = realloc(*fds, (nb_fds + 1) * sizeof(int));
>  			if (!tmp) {
> @@ -820,10 +830,6 @@ int prog_parse_fds(int *argc, char ***argv, int **fds)
>  		NEXT_ARGP();
>  
>  		name = **argv;
> -		if (strlen(name) > BPF_OBJ_NAME_LEN - 1) {
> -			p_err("can't parse name");
> -			return -1;
> -		}

Why removing the check? Just update the bound to MAX_PROG_FULL_NAME - 1?

>  		NEXT_ARGP();
>  
>  		return prog_fd_by_nametag(name, fds, false);