Re: [PATCH bpf 8/9] selftests/bpf: Add write tests for sk storage map iterator

[Yonghong Song <yhs@xxxxxx>]

On 8/6/22 12:40 AM, Hou Tao wrote:
> From: Hou Tao <houtao1@xxxxxxxxxx>
>
> Add test to validate the overwrite of sock storage map value in map
> iterator and another one to ensure out-of-bound value writing is
> rejected.
>
> Signed-off-by: Hou Tao <houtao1@xxxxxxxxxx>

One nit below.

Acked-by: Yonghong Song <yhs@xxxxxx>

> ---
>   .../selftests/bpf/prog_tests/bpf_iter.c       | 20 +++++++++++++++++--
>   .../bpf/progs/bpf_iter_bpf_sk_storage_map.c   | 20 ++++++++++++++++++-
>   2 files changed, 37 insertions(+), 3 deletions(-)
>
> diff --git a/tools/testing/selftests/bpf/prog_tests/bpf_iter.c b/tools/testing/selftests/bpf/prog_tests/bpf_iter.c
> index 94c2c8df3fe4..f75308d75570 100644
> --- a/tools/testing/selftests/bpf/prog_tests/bpf_iter.c
> +++ b/tools/testing/selftests/bpf/prog_tests/bpf_iter.c
> @@ -1074,7 +1074,7 @@ static void test_bpf_sk_stoarge_map_iter_fd(void)
>   	if (!ASSERT_OK_PTR(skel, "bpf_iter_bpf_sk_storage_map__open_and_load"))
>   		return;
>   
> -	do_read_map_iter_fd(&skel->skeleton, skel->progs.dump_bpf_sk_storage_map,
> +	do_read_map_iter_fd(&skel->skeleton, skel->progs.rw_bpf_sk_storage_map,
>   			    skel->maps.sk_stg_map);
>   
>   	bpf_iter_bpf_sk_storage_map__destroy(skel);
> @@ -1115,7 +1115,15 @@ static void test_bpf_sk_storage_map(void)
>   	linfo.map.map_fd = map_fd;
>   	opts.link_info = &linfo;
>   	opts.link_info_len = sizeof(linfo);
> -	link = bpf_program__attach_iter(skel->progs.dump_bpf_sk_storage_map, &opts);
> +	link = bpf_program__attach_iter(skel->progs.oob_write_bpf_sk_storage_map, &opts);
> +	err = libbpf_get_error(link);
> +	if (!ASSERT_EQ(err, -EACCES, "attach_oob_write_iter")) {
> +		if (!err)
> +			bpf_link__destroy(link);
> +		goto out;
> +	}
> +
> +	link = bpf_program__attach_iter(skel->progs.rw_bpf_sk_storage_map, &opts);
>   	if (!ASSERT_OK_PTR(link, "attach_iter"))
>   		goto out;
>   
> @@ -1123,6 +1131,7 @@ static void test_bpf_sk_storage_map(void)
>   	if (!ASSERT_GE(iter_fd, 0, "create_iter"))
>   		goto free_link;
>   
> +	skel->bss->to_add_val = time(NULL);
>   	/* do some tests */
>   	while ((len = read(iter_fd, buf, sizeof(buf))) > 0)
>   		;
> @@ -1136,6 +1145,13 @@ static void test_bpf_sk_storage_map(void)
>   	if (!ASSERT_EQ(skel->bss->val_sum, expected_val, "val_sum"))
>   		goto close_iter;
>   
> +	for (i = 0; i < num_sockets; i++) {
> +		err = bpf_map_lookup_elem(map_fd, &sock_fd[i], &val);
> +		if (!ASSERT_OK(err, "map_lookup") ||
> +		    !ASSERT_EQ(val, i + 1 + skel->bss->to_add_val, "check_map_value"))
> +			break;
> +	}
> +
>   close_iter:
>   	close(iter_fd);
>   free_link:
> diff --git a/tools/testing/selftests/bpf/progs/bpf_iter_bpf_sk_storage_map.c b/tools/testing/selftests/bpf/progs/bpf_iter_bpf_sk_storage_map.c
> index 6b70ccaba301..6a82f8b0c0fa 100644
> --- a/tools/testing/selftests/bpf/progs/bpf_iter_bpf_sk_storage_map.c
> +++ b/tools/testing/selftests/bpf/progs/bpf_iter_bpf_sk_storage_map.c
> @@ -16,9 +16,10 @@ struct {
>   
>   __u32 val_sum = 0;
>   __u32 ipv6_sk_count = 0;
> +__u32 to_add_val = 0;
>   
>   SEC("iter/bpf_sk_storage_map")
> -int dump_bpf_sk_storage_map(struct bpf_iter__bpf_sk_storage_map *ctx)
> +int rw_bpf_sk_storage_map(struct bpf_iter__bpf_sk_storage_map *ctx)
>   {
>   	struct sock *sk = ctx->sk;
>   	__u32 *val = ctx->value;
> @@ -30,5 +31,22 @@ int dump_bpf_sk_storage_map(struct bpf_iter__bpf_sk_storage_map *ctx)
>   		ipv6_sk_count++;
>   
>   	val_sum += *val;
> +
> +	*val += to_add_val;
> +
> +	return 0;
> +}
> +
> +SEC("iter/bpf_sk_storage_map")
> +int oob_write_bpf_sk_storage_map(struct bpf_iter__bpf_sk_storage_map *ctx)
> +{
> +	struct sock *sk = ctx->sk;
> +	__u32 *val = ctx->value;
> +
> +	if (sk == (void *)0 || val == (void *)0)

Newer bpf_helpers.h provides NULL for (void *)0, you can use NULL now.

> +		return 0;
> +
> +	*(val + 1) = 0xdeadbeef;
> +
>   	return 0;
>   }