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

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On Fri, Jul 29, 2022 at 2:53 AM Quentin Monnet <quentin@xxxxxxxxxxxxx> wrote:
>
> On 29/07/2022 07:18, Manu Bretelle wrote:
> > From: chantra <chantr4@xxxxxxxxx>
> >
> > 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
>

Thanks for the feedback and providing relevant links. I will amend the
commit to reflect your feedback. Markdown was an artifact of this
being a GH PR originally. I will go for plaintext.


> > ---
> >  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
>

Both are NULL terminated, but I am happy to add the extra safeguard.

> > +                             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);
>

Make sense. Will do.



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