On Mon, Sep 27, 2021 at 8:00 AM Kumar Kartikeya Dwivedi
<memxor@xxxxxxxxx> wrote:
>
> When the loader indicates an internal error (result of a checked bpf
> system call), it returns the result in attr.test.retval. However, tests
> that rely on ASSERT_OK_PTR on NULL (returned from light skeleton) may
> miss that NULL denotes an error if errno is set to 0. This would result
> in skel pointer being NULL, while ASSERT_OK_PTR returning 1, leading to
> a SEGV on dereference of skel, because libbpf_get_error relies on the
> assumption that errno is always set in case of error for ptr == NULL.
>
> In particular, this was observed for the ksyms_module test. When
> executed using `./test_progs -t ksyms`, prior tests manipulated errno
> and the test didn't crash when it failed at ksyms_module load, while
> using `./test_progs -t ksyms_module` crashed due to errno being
> untouched.
>
> Fixes: 67234743736a (libbpf: Generate loader program out of BPF ELF file.)
> Signed-off-by: Kumar Kartikeya Dwivedi <memxor@xxxxxxxxx>
> ---
> tools/lib/bpf/skel_internal.h | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/tools/lib/bpf/skel_internal.h b/tools/lib/bpf/skel_internal.h
> index b22b50c1b173..9cf66702fa8d 100644
> --- a/tools/lib/bpf/skel_internal.h
> +++ b/tools/lib/bpf/skel_internal.h
> @@ -105,10 +105,12 @@ static inline int bpf_load_and_run(struct bpf_load_and_run_opts *opts)
> err = skel_sys_bpf(BPF_PROG_RUN, &attr, sizeof(attr));
> if (err < 0 || (int)attr.test.retval < 0) {
> opts->errstr = "failed to execute loader prog";
> - if (err < 0)
> + if (err < 0) {
> err = -errno;
> - else
> + } else {
> err = (int)attr.test.retval;
> + errno = -err;
> + }
Applied this fix as well, since I hit this bug too :)
Thanks!
