Re: [PATCH bpf-next v4 6/6] selftests/bpf: Add a series of tests for bpf_snprintf

From: Andrii Nakryiko <andrii.nakryiko@gmail.com>
To: Florent Revest <revest@chromium.org>
Cc: bpf <bpf@vger.kernel.org>, Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Andrii Nakryiko <andrii@kernel.org>, Yonghong Song <yhs@fb.com>,
	KP Singh <kpsingh@kernel.org>,
	Brendan Jackman <jackmanb@chromium.org>,
	open list <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH bpf-next v4 6/6] selftests/bpf: Add a series of tests for bpf_snprintf
Date: Thu, 15 Apr 2021 16:20:21 -0700	[thread overview]
Message-ID: <CAEf4BzYtOOwDLOGmfQ+pF5t-muDXQB_StFB7SQS6Ap78P5FjQQ@mail.gmail.com> (raw)
In-Reply-To: <20210414185406.917890-7-revest@chromium.org>

On Wed, Apr 14, 2021 at 11:54 AM Florent Revest <revest@chromium.org> wrote:
>
> The "positive" part tests all format specifiers when things go well.
>
> The "negative" part makes sure that incorrect format strings fail at
> load time.
>
> Signed-off-by: Florent Revest <revest@chromium.org>
> ---
>  .../selftests/bpf/prog_tests/snprintf.c       | 124 ++++++++++++++++++
>  .../selftests/bpf/progs/test_snprintf.c       |  73 +++++++++++
>  .../bpf/progs/test_snprintf_single.c          |  20 +++
>  3 files changed, 217 insertions(+)
>  create mode 100644 tools/testing/selftests/bpf/prog_tests/snprintf.c
>  create mode 100644 tools/testing/selftests/bpf/progs/test_snprintf.c
>  create mode 100644 tools/testing/selftests/bpf/progs/test_snprintf_single.c
>

[...]

> +/* Loads an eBPF object calling bpf_snprintf with up to 10 characters of fmt */
> +static int load_single_snprintf(char *fmt)
> +{
> +       struct test_snprintf_single *skel;
> +       int ret;
> +
> +       skel = test_snprintf_single__open();
> +       if (!skel)
> +               return -EINVAL;
> +
> +       memcpy(skel->rodata->fmt, fmt, min(strlen(fmt) + 1, 10));
> +
> +       ret = test_snprintf_single__load(skel);
> +       if (!ret)
> +               test_snprintf_single__destroy(skel);

destroy unconditionally?

> +
> +       return ret;
> +}
> +
> +void test_snprintf_negative(void)
> +{
> +       ASSERT_OK(load_single_snprintf("valid %d"), "valid usage");
> +
> +       ASSERT_ERR(load_single_snprintf("0123456789"), "no terminating zero");
> +       ASSERT_ERR(load_single_snprintf("%d %d"), "too many specifiers");
> +       ASSERT_ERR(load_single_snprintf("%pi5"), "invalid specifier 1");
> +       ASSERT_ERR(load_single_snprintf("%a"), "invalid specifier 2");
> +       ASSERT_ERR(load_single_snprintf("%"), "invalid specifier 3");
> +       ASSERT_ERR(load_single_snprintf("\x80"), "non ascii character");
> +       ASSERT_ERR(load_single_snprintf("\x1"), "non printable character");

Some more cases that came up in my mind:

1. %123987129387192387 -- long and unterminated specified
2. similarly %------- or something like that

Do you think they are worth checking?

> +}
> +
> +void test_snprintf(void)
> +{
> +       if (test__start_subtest("snprintf_positive"))
> +               test_snprintf_positive();
> +       if (test__start_subtest("snprintf_negative"))
> +               test_snprintf_negative();
> +}

[...]

> +char _license[] SEC("license") = "GPL";
> diff --git a/tools/testing/selftests/bpf/progs/test_snprintf_single.c b/tools/testing/selftests/bpf/progs/test_snprintf_single.c
> new file mode 100644
> index 000000000000..15ccc5c43803
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/progs/test_snprintf_single.c
> @@ -0,0 +1,20 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/* Copyright (c) 2021 Google LLC. */
> +
> +#include <linux/bpf.h>
> +#include <bpf/bpf_helpers.h>
> +
> +// The format string is filled from the userspace side such that loading fails

C++ style format

> +static const char fmt[10];
> +
> +SEC("raw_tp/sys_enter")
> +int handler(const void *ctx)
> +{
> +       unsigned long long arg = 42;
> +
> +       bpf_snprintf(NULL, 0, fmt, &arg, sizeof(arg));
> +
> +       return 0;
> +}
> +
> +char _license[] SEC("license") = "GPL";
> --
> 2.31.1.295.g9ea45b61b8-goog
>