selftests/bpf: Refactor bpf_get_ksyms() trace helper

ASAN reported a memory leak in bpf_get_ksyms(): it allocates a struct
ksyms internally and never frees it.

Move struct ksyms to trace_helpers.h and return it from the
bpf_get_ksyms(), giving ownership to the caller. Add filtered_syms and
filtered_cnt fields to the ksyms to hold the filtered array of
symbols, previously returned by bpf_get_ksyms().

Fixup the call sites: kprobe_multi_test and bench_trigger.

Signed-off-by: Ihor Solodrai <ihor.solodrai@linux.dev>
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20260223190736.649171-10-ihor.solodrai@linux.dev
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

tools/testing/selftests/bpf/benchs/bench_trigger.c

@@ -230,8 +230,8 @@ static void trigger_fentry_setup(void)
 static void attach_ksyms_all(struct bpf_program *empty, bool kretprobe)
 {
 	LIBBPF_OPTS(bpf_kprobe_multi_opts, opts);
-	char **syms = NULL;
-	size_t cnt = 0;
+	struct bpf_link *link = NULL;
+	struct ksyms *ksyms = NULL;
 
 	/* Some recursive functions will be skipped in
 	 * bpf_get_ksyms -> skip_entry, as they can introduce sufficient
@@ -241,16 +241,18 @@ static void attach_ksyms_all(struct bpf_program *empty, bool kretprobe)
 	 * So, don't run the kprobe-multi-all and kretprobe-multi-all on
 	 * a debug kernel.
 	 */
-	if (bpf_get_ksyms(&syms, &cnt, true)) {
+	if (bpf_get_ksyms(&ksyms, true)) {
 		fprintf(stderr, "failed to get ksyms\n");
 		exit(1);
 	}
 
-	opts.syms = (const char **) syms;
-	opts.cnt = cnt;
+	opts.syms = (const char **)ksyms->filtered_syms;
+	opts.cnt = ksyms->filtered_cnt;
 	opts.retprobe = kretprobe;
 	/* attach empty to all the kernel functions except bpf_get_numa_node_id. */
-	if (!bpf_program__attach_kprobe_multi_opts(empty, NULL, &opts)) {
+	link = bpf_program__attach_kprobe_multi_opts(empty, NULL, &opts);
+	free_kallsyms_local(ksyms);
+	if (!link) {
 		fprintf(stderr, "failed to attach bpf_program__attach_kprobe_multi_opts to all\n");
 		exit(1);
 	}

tools/testing/selftests/bpf/prog_tests/kprobe_multi_test.c

@@ -456,25 +456,23 @@ static void test_kprobe_multi_bench_attach(bool kernel)
 {
 	LIBBPF_OPTS(bpf_kprobe_multi_opts, opts);
 	struct kprobe_multi_empty *skel = NULL;
-	char **syms = NULL;
-	size_t cnt = 0;
+	struct ksyms *ksyms = NULL;
 
-	if (!ASSERT_OK(bpf_get_ksyms(&syms, &cnt, kernel), "bpf_get_ksyms"))
+	if (!ASSERT_OK(bpf_get_ksyms(&ksyms, kernel), "bpf_get_ksyms"))
 		return;
 
 	skel = kprobe_multi_empty__open_and_load();
 	if (!ASSERT_OK_PTR(skel, "kprobe_multi_empty__open_and_load"))
 		goto cleanup;
 
-	opts.syms = (const char **) syms;
-	opts.cnt = cnt;
+	opts.syms = (const char **)ksyms->filtered_syms;
+	opts.cnt = ksyms->filtered_cnt;
 
 	do_bench_test(skel, &opts);
 
 cleanup:
 	kprobe_multi_empty__destroy(skel);
-	if (syms)
-		free(syms);
+	free_kallsyms_local(ksyms);
 }
 
 static void test_kprobe_multi_bench_attach_addr(bool kernel)

tools/testing/selftests/bpf/trace_helpers.c

@@ -24,12 +24,6 @@
 #define TRACEFS_PIPE	"/sys/kernel/tracing/trace_pipe"
 #define DEBUGFS_PIPE	"/sys/kernel/debug/tracing/trace_pipe"
 
-struct ksyms {
-	struct ksym *syms;
-	size_t sym_cap;
-	size_t sym_cnt;
-};
-
 static struct ksyms *ksyms;
 static pthread_mutex_t ksyms_mutex = PTHREAD_MUTEX_INITIALIZER;
 
@@ -54,6 +48,8 @@ void free_kallsyms_local(struct ksyms *ksyms)
 	if (!ksyms)
 		return;
 
+	free(ksyms->filtered_syms);
+
 	if (!ksyms->syms) {
 		free(ksyms);
 		return;
@@ -610,7 +606,7 @@ static int search_kallsyms_compare(const void *p1, const struct ksym *p2)
 	return compare_name(p1, p2->name);
 }
 
-int bpf_get_ksyms(char ***symsp, size_t *cntp, bool kernel)
+int bpf_get_ksyms(struct ksyms **ksymsp, bool kernel)
 {
 	size_t cap = 0, cnt = 0;
 	char *name = NULL, *ksym_name, **syms = NULL;
@@ -637,8 +633,10 @@ int bpf_get_ksyms(char ***symsp, size_t *cntp, bool kernel)
 	else
 		f = fopen("/sys/kernel/debug/tracing/available_filter_functions", "r");
 
-	if (!f)
+	if (!f) {
+		free_kallsyms_local(ksyms);
 		return -EINVAL;
+	}
 
 	map = hashmap__new(symbol_hash, symbol_equal, NULL);
 	if (IS_ERR(map)) {
@@ -679,15 +677,18 @@ int bpf_get_ksyms(char ***symsp, size_t *cntp, bool kernel)
 		syms[cnt++] = ksym_name;
 	}
 
-	*symsp = syms;
-	*cntp = cnt;
+	ksyms->filtered_syms = syms;
+	ksyms->filtered_cnt = cnt;
+	*ksymsp = ksyms;
 
 error:
 	free(name);
 	fclose(f);
 	hashmap__free(map);
-	if (err)
+	if (err) {
 		free(syms);
+		free_kallsyms_local(ksyms);
+	}
 	return err;
 }
 

tools/testing/selftests/bpf/trace_helpers.h

@@ -23,7 +23,14 @@ struct ksym {
 	long addr;
 	char *name;
 };
-struct ksyms;
+
+struct ksyms {
+	struct ksym *syms;
+	size_t sym_cap;
+	size_t sym_cnt;
+	char **filtered_syms;
+	size_t filtered_cnt;
+};
 
 typedef int (*ksym_cmp_t)(const void *p1, const void *p2);
 typedef int (*ksym_search_cmp_t)(const void *p1, const struct ksym *p2);
@@ -53,7 +60,7 @@ ssize_t get_rel_offset(uintptr_t addr);
 
 int read_build_id(const char *path, char *build_id, size_t size);
 
-int bpf_get_ksyms(char ***symsp, size_t *cntp, bool kernel);
+int bpf_get_ksyms(struct ksyms **ksymsp, bool kernel);
 int bpf_get_addrs(unsigned long **addrsp, size_t *cntp, bool kernel);
 
 #endif