linux-kernel - Re: [RESEND][PATCH 6/6] selftests/bpf: Add tests for _opts variants of bpf_*_get_fd_by

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Date:   Wed, 5 Oct 2022 16:13:33 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Roberto Sassu <roberto.sassu@...weicloud.com>
Cc:     ast@...nel.org, daniel@...earbox.net, andrii@...nel.org,
        martin.lau@...ux.dev, song@...nel.org, yhs@...com,
        john.fastabend@...il.com, kpsingh@...nel.org, sdf@...gle.com,
        haoluo@...gle.com, jolsa@...nel.org, mykolal@...com,
        shuah@...nel.org, bpf@...r.kernel.org,
        linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org,
        Roberto Sassu <roberto.sassu@...wei.com>
Subject: Re: [RESEND][PATCH 6/6] selftests/bpf: Add tests for _opts variants
 of bpf_*_get_fd_by_id()

On Tue, Oct 4, 2022 at 6:19 AM Roberto Sassu
<roberto.sassu@...weicloud.com> wrote:
>
> From: Roberto Sassu <roberto.sassu@...wei.com>
>
> Introduce the data_input map, write-protected with a small eBPF program
> implementing the lsm/bpf_map hook.
>
> Then, ensure that bpf_map_get_fd_by_id() and bpf_map_get_fd_by_id_opts()
> with NULL opts don't succeed due to requesting read-write access to the
> write-protected map. Also, ensure that bpf_map_get_fd_by_id_opts() with
> open_flags in opts set to BPF_F_RDONLY instead succeeds.
>
> After obtaining a read-only fd, ensure that only map lookup succeeds and
> not update. Ensure that update works only with the read-write fd obtained
> at program loading time, when the write protection was not yet enabled.
>
> Finally, ensure that the other _opts variants of bpf_*_get_fd_by_id() don't
> work if the BPF_F_RDONLY flag is set in opts (due to the kernel not
> handling the open_flags member of bpf_attr).
>
> Signed-off-by: Roberto Sassu <roberto.sassu@...wei.com>
> ---
>  tools/testing/selftests/bpf/DENYLIST.s390x    |  1 +
>  .../bpf/prog_tests/libbpf_get_fd_opts.c       | 88 +++++++++++++++++++
>  .../bpf/progs/test_libbpf_get_fd_opts.c       | 36 ++++++++
>  3 files changed, 125 insertions(+)
>  create mode 100644 tools/testing/selftests/bpf/prog_tests/libbpf_get_fd_opts.c
>  create mode 100644 tools/testing/selftests/bpf/progs/test_libbpf_get_fd_opts.c
>
> diff --git a/tools/testing/selftests/bpf/DENYLIST.s390x b/tools/testing/selftests/bpf/DENYLIST.s390x
> index 17e074eb42b8..780a9b2090ad 100644
> --- a/tools/testing/selftests/bpf/DENYLIST.s390x
> +++ b/tools/testing/selftests/bpf/DENYLIST.s390x
> @@ -75,3 +75,4 @@ user_ringbuf                             # failed to find kernel BTF type ID of
>  lookup_key                               # JIT does not support calling kernel function                                (kfunc)
>  verify_pkcs7_sig                         # JIT does not support calling kernel function                                (kfunc)
>  kfunc_dynptr_param                       # JIT does not support calling kernel function                                (kfunc)
> +libbpf_get_fd_opts                       # failed to attach: ERROR: strerror_r(-524)=22                                (trampoline)
> diff --git a/tools/testing/selftests/bpf/prog_tests/libbpf_get_fd_opts.c b/tools/testing/selftests/bpf/prog_tests/libbpf_get_fd_opts.c
> new file mode 100644
> index 000000000000..2d4ba8f80d55
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/prog_tests/libbpf_get_fd_opts.c
> @@ -0,0 +1,88 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +/*
> + * Copyright (C) 2022 Huawei Technologies Duesseldorf GmbH
> + *
> + * Author: Roberto Sassu <roberto.sassu@...wei.com>
> + */
> +
> +#include <test_progs.h>
> +
> +#include "test_libbpf_get_fd_opts.skel.h"
> +
> +void test_libbpf_get_fd_opts(void)
> +{
> +       struct test_libbpf_get_fd_opts *skel;
> +       struct bpf_map_info info_m = { 0 };

1) this 0 is misleading, it's initializing only first field
(explicitly), all the other ones are implicitly initialized with
zeroes as well. In short, just use = {} to zero-initialize structs, in
general.

> +       __u32 len = sizeof(info_m), value;
> +       struct bpf_map *map;
> +       int ret, zero = 0, fd = -1;
> +
> +       DECLARE_LIBBPF_OPTS(bpf_get_fd_opts, fd_opts_rdonly,
> +               .open_flags = BPF_F_RDONLY,
> +       );

LIBBPF_OPTS() macro defines variable, so don't add empty line before
it, it should be part of variable declaration section. Also use
shorter LIBBPF_OPTS() macro instead.


> +
> +       skel = test_libbpf_get_fd_opts__open_and_load();
> +       if (!ASSERT_OK_PTR(skel, "test_libbpf_get_fd_opts__open_and_load"))
> +               return;
> +
> +       ret = test_libbpf_get_fd_opts__attach(skel);
> +       if (!ASSERT_OK(ret, "test_libbpf_get_fd_opts__attach"))
> +               goto close_prog;
> +
> +       map = bpf_object__find_map_by_name(skel->obj, "data_input");
> +       if (!ASSERT_OK_PTR(map, "bpf_object__find_map_by_name"))
> +               goto close_prog;

why find_map_by_name, you have that same map as skel->maps.data_input

> +
> +       ret = bpf_obj_get_info_by_fd(bpf_map__fd(map), &info_m, &len);
> +       if (!ASSERT_OK(ret, "bpf_obj_get_info_by_fd"))
> +               goto close_prog;

[...]

> +       /* BTF get fd with opts set should not work (no kernel support). */
> +       ret = bpf_btf_get_fd_by_id_opts(0, &fd_opts_rdonly);
> +       ASSERT_EQ(ret, -EINVAL, "bpf_btf_get_fd_by_id_opts");
> +
> +close_prog:
> +       close(fd);

if (fd >= 0) is missing

> +       test_libbpf_get_fd_opts__destroy(skel);
> +}

[...]