linux-kernel - Re: [PATCH] selftests/bpf: Add test for trie_get_next

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Message-ID: <7affe124-770d-a31b-c588-4492e45297cc@huaweicloud.com>
Date: Fri, 25 Oct 2024 19:53:35 +0800
From: Hou Tao <houtao@...weicloud.com>
To: Byeonguk Jeong <jungbu2855@...il.com>,
 Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc: Daniel Borkmann <daniel@...earbox.net>,
 Yonghong Song <yonghong.song@...ux.dev>, bpf <bpf@...r.kernel.org>,
 LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] selftests/bpf: Add test for trie_get_next_key()

Hi,

On 10/24/2024 5:08 PM, Byeonguk Jeong wrote:
> Add a test for out-of-bounds write in trie_get_next_key() when a full
> path from root to leaf exists and bpf_map_get_next_key() is called
> with the leaf node. It may crashes the kernel on failure, so please
> run in a VM.
>
> Signed-off-by: Byeonguk Jeong <jungbu2855@...il.com>
> ---
>  .../bpf/map_tests/lpm_trie_map_get_next_key.c | 115 ++++++++++++++++++
>  1 file changed, 115 insertions(+)
>  create mode 100644 tools/testing/selftests/bpf/map_tests/lpm_trie_map_get_next_key.c
>
> diff --git a/tools/testing/selftests/bpf/map_tests/lpm_trie_map_get_next_key.c b/tools/testing/selftests/bpf/map_tests/lpm_trie_map_get_next_key.c
> new file mode 100644
> index 000000000000..85b916b69411
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/map_tests/lpm_trie_map_get_next_key.c
> @@ -0,0 +1,115 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +/*
> + * WARNING
> + * -------
> + *  This test suite may crash the kernel, thus should be run in a VM.
> + */
> +

The comments above are unnecessary, please remove it.
> +#define _GNU_SOURCE
> +#include <linux/bpf.h>
> +#include <stdio.h>
> +#include <stdbool.h>
> +#include <unistd.h>
> +#include <errno.h>
> +#include <stdlib.h>
> +#include <string.h>
> +#include <pthread.h>
> +
> +#include <bpf/bpf.h>
> +#include <bpf/libbpf.h>
> +
> +#include <test_maps.h>
> +
> +struct test_lpm_key {
> +	__u32 prefix;
> +	__u32 data;
> +};
> +
> +struct get_next_key_ctx {
> +	struct test_lpm_key key;
> +	bool start;
> +	bool stop;
> +	int map_fd;
> +	int loop;
> +};
> +
> +static void *get_next_key_fn(void *arg)
> +{
> +	struct get_next_key_ctx *ctx = arg;
> +	struct test_lpm_key next_key;
> +	int i;

int i = 0;
> +
> +	while (!ctx->start)
> +		usleep(1);
> +
> +	while (!ctx->stop && i++ < ctx->loop)
> +		bpf_map_get_next_key(ctx->map_fd, &ctx->key, &next_key);
> +
> +	return NULL;
> +}
> +
> +static void abort_get_next_key(struct get_next_key_ctx *ctx, pthread_t *tids,
> +			       unsigned int nr)
> +{
> +	unsigned int i;
> +
> +	ctx->stop = true;
> +	ctx->start = true;
> +	for (i = 0; i < nr; i++)
> +		pthread_join(tids[i], NULL);
> +}
> +
> +/* This test aims to prevent regression of future. As long as the kernel does
> + * not panic, it is considered as success.
> + */
> +void test_lpm_trie_map_get_next_key(void)
> +{
> +#define MAX_NR_THREADS 256

Are 8 threads sufficient to reproduce the problem ?
> +	LIBBPF_OPTS(bpf_map_create_opts, create_opts,
> +		    .map_flags = BPF_F_NO_PREALLOC);
> +	struct test_lpm_key key = {};
> +	__u32 val = 0;
> +	int map_fd;
> +	const __u32 max_prefixlen = 8 * (sizeof(key) - sizeof(key.prefix));
> +	const __u32 max_entries = max_prefixlen + 1;
> +	unsigned int i, nr = MAX_NR_THREADS, loop = 4096;
> +	pthread_t tids[MAX_NR_THREADS];
> +	struct get_next_key_ctx ctx;
> +	int err;
> +
> +	map_fd = bpf_map_create(BPF_MAP_TYPE_LPM_TRIE, "lpm_trie_map",
> +				sizeof(struct test_lpm_key), sizeof(__u32),
> +				max_entries, &create_opts);
> +	CHECK(map_fd == -1, "bpf_map_create(), error:%s\n",
> +	      strerror(errno));

CHECK(map_fd == -1, "bpf_map_create()", "error:%s\n", strerror(errno));
It seems you didn't build test it.
> +
> +	for (i = 0; i <= max_prefixlen; i++) {
> +		key.prefix = i;
> +		err = bpf_map_update_elem(map_fd, &key, &val, BPF_ANY);
> +		CHECK(err, "bpf_map_update_elem()", "error:%s\n",
> +		      strerror(errno));
> +	}
> +
> +	ctx.start = false;
> +	ctx.stop = false;
> +	ctx.map_fd = map_fd;
> +	ctx.loop = loop;
> +	memcpy(&ctx.key, &key, sizeof(key));
> +
> +	for (i = 0; i < nr; i++) {
> +		err = pthread_create(&tids[i], NULL, get_next_key_fn, &ctx);
> +		if (err) {
> +			abort_get_next_key(&ctx, tids, i);
> +			CHECK(err, "pthread_create", "error %d\n", err);
> +		}
> +	}
> +
> +	ctx.start = true;
> +	for (i = 0; i < nr; i++)
> +		pthread_join(tids[i], NULL);
> +
> +	printf("%s:PASS\n", __func__);
> +
> +	close(map_fd);
> +}