Re: [PATCH bpf-next v1 04/14] selftests/bpf: Refactor bpf_get_ksyms() trace helper

[Jiri Olsa]

On Wed, Feb 11, 2026 at 05:13:46PM -0800, Ihor Solodrai wrote:
> ASAN reported a memory leak in bpf_get_ksyms(): it allocates a struct
> ksyms internally and never frees it.
> 
> Moe 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@xxxxxxxxx>
> ---
>  .../selftests/bpf/benchs/bench_trigger.c      |  9 ++++----
>  .../bpf/prog_tests/kprobe_multi_test.c        | 12 ++++------
>  tools/testing/selftests/bpf/trace_helpers.c   | 23 ++++++++++---------
>  tools/testing/selftests/bpf/trace_helpers.h   | 11 +++++++--
>  4 files changed, 30 insertions(+), 25 deletions(-)
> 
> diff --git a/tools/testing/selftests/bpf/benchs/bench_trigger.c b/tools/testing/selftests/bpf/benchs/bench_trigger.c
> index aeec9edd3851..7231b88cf21a 100644
> --- a/tools/testing/selftests/bpf/benchs/bench_trigger.c
> +++ b/tools/testing/selftests/bpf/benchs/bench_trigger.c
> @@ -230,8 +230,7 @@ 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 ksyms *ksyms = NULL;
>  
>  	/* Some recursive functions will be skipped in
>  	 * bpf_get_ksyms -> skip_entry, as they can introduce sufficient
> @@ -241,13 +240,13 @@ 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)) {

hi,

missing free_kallsyms_local call in here ?


> diff --git a/tools/testing/selftests/bpf/prog_tests/kprobe_multi_test.c b/tools/testing/selftests/bpf/prog_tests/kprobe_multi_test.c
> index 9caef222e528..f81dcd609ee9 100644
> --- a/tools/testing/selftests/bpf/prog_tests/kprobe_multi_test.c
> +++ b/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)
> diff --git a/tools/testing/selftests/bpf/trace_helpers.c b/tools/testing/selftests/bpf/trace_helpers.c
> index eeaab7013ca2..0e63daf83ed5 100644
> --- a/tools/testing/selftests/bpf/trace_helpers.c
> +++ b/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);
> +	}

I think we could just call free_kallsyms_local unconditionally in here
and fix callers to free syms pointer? seems easier than adding filtered*
fields to ksyms

thanks,
jirak


>  	return err;
>  }
>  
> diff --git a/tools/testing/selftests/bpf/trace_helpers.h b/tools/testing/selftests/bpf/trace_helpers.h
> index a5576b2dfc26..d5bf1433675d 100644
> --- a/tools/testing/selftests/bpf/trace_helpers.h
> +++ b/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
> -- 
> 2.53.0
> 
>