selftests/bpf: Add test for trie_get_next_key()

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 <[e-mail]>
Acked-by: Hou Tao <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Alexei Starovoitov <[e-mail]>

tools/testing/selftests/bpf/map_tests/lpm_trie_map_get_next_key.c

···
+// SPDX-License-Identifier: GPL-2.0
+
+#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 = 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 8
+	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 = 65536;
+	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));
+
+	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);
+}