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From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
To: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Cc: bpf <bpf@vger.kernel.org>, "Alexei Starovoitov" <ast@kernel.org>,
	"Daniel Borkmann" <daniel@iogearbox.net>,
	"Andrii Nakryiko" <andrii@kernel.org>,
	"Martin KaFai Lau" <kafai@fb.com>,
	"Song Liu" <songliubraving@fb.com>, "Yonghong Song" <yhs@fb.com>,
	"Jesper Dangaard Brouer" <brouer@redhat.com>,
	"Toke Høiland-Jørgensen" <toke@redhat.com>,
	"Network Development" <netdev@vger.kernel.org>
Subject: Re: [PATCH bpf-next v5 10/12] libbpf: Fix skel_internal.h to set errno on loader retval < 0
Date: Wed, 29 Sep 2021 20:45:17 -0700	[thread overview]
Message-ID: <CAADnVQKBBswOOsdpNsaxtTprSkcAvL3ggVV8g0A-mUjs4_ucaQ@mail.gmail.com> (raw)
In-Reply-To: <20210927145941.1383001-11-memxor@gmail.com>

On Mon, Sep 27, 2021 at 8:00 AM Kumar Kartikeya Dwivedi
<memxor@gmail.com> 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@gmail.com>
> ---
>  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!

  reply	other threads:[~2021-09-30  3:45 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-27 14:59 [PATCH bpf-next v5 00/12] Support kernel module function calls from eBPF Kumar Kartikeya Dwivedi
2021-09-27 14:59 ` [PATCH bpf-next v5 01/12] bpf: Introduce BPF support for kernel module function calls Kumar Kartikeya Dwivedi
2021-09-27 14:59 ` [PATCH bpf-next v5 02/12] bpf: Be conservative while processing invalid kfunc calls Kumar Kartikeya Dwivedi
2021-09-27 14:59 ` [PATCH bpf-next v5 03/12] bpf: btf: Introduce helpers for dynamic BTF set registration Kumar Kartikeya Dwivedi
2021-09-27 14:59 ` [PATCH bpf-next v5 04/12] tools: Allow specifying base BTF file in resolve_btfids Kumar Kartikeya Dwivedi
2021-09-27 14:59 ` [PATCH bpf-next v5 05/12] bpf: Enable TCP congestion control kfunc from modules Kumar Kartikeya Dwivedi
2021-09-27 14:59 ` [PATCH bpf-next v5 06/12] libbpf: Support kernel module function calls Kumar Kartikeya Dwivedi
2021-09-27 14:59 ` [PATCH bpf-next v5 07/12] libbpf: Resolve invalid weak kfunc calls with imm = 0, off = 0 Kumar Kartikeya Dwivedi
2021-09-27 14:59 ` [PATCH bpf-next v5 08/12] libbpf: Make gen_loader data aligned Kumar Kartikeya Dwivedi
2021-09-29 20:50   ` Alexei Starovoitov
2021-09-27 14:59 ` [PATCH bpf-next v5 09/12] libbpf: Update gen_loader to emit BTF_KIND_FUNC relocations Kumar Kartikeya Dwivedi
2021-09-29  0:01   ` Alexei Starovoitov
2021-09-29  0:10     ` Kumar Kartikeya Dwivedi
2021-09-27 14:59 ` [PATCH bpf-next v5 10/12] libbpf: Fix skel_internal.h to set errno on loader retval < 0 Kumar Kartikeya Dwivedi
2021-09-30  3:45   ` Alexei Starovoitov [this message]
2021-09-27 14:59 ` [PATCH bpf-next v5 11/12] bpf: selftests: Fix fd cleanup in get_branch_snapshot Kumar Kartikeya Dwivedi
2021-09-28 23:58   ` Song Liu
2021-09-29 20:26     ` Alexei Starovoitov
2021-09-27 14:59 ` [PATCH bpf-next v5 12/12] bpf: selftests: Add selftests for module kfunc support Kumar Kartikeya Dwivedi

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