linux-kernel - Re: [PATCH bpf v3 4/6] selftest/bpf: Fix memory leak in kprobe_multi

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Date:   Mon, 10 Oct 2022 18:34:58 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Xu Kuohai <xukuohai@...wei.com>
Cc:     bpf@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-kselftest@...r.kernel.org, netdev@...r.kernel.org,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Song Liu <song@...nel.org>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Stanislav Fomichev <sdf@...gle.com>,
        Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
        Mykola Lysenko <mykolal@...com>, Shuah Khan <shuah@...nel.org>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        Kumar Kartikeya Dwivedi <memxor@...il.com>,
        Alan Maguire <alan.maguire@...cle.com>,
        Delyan Kratunov <delyank@...com>,
        Lorenzo Bianconi <lorenzo@...nel.org>
Subject: Re: [PATCH bpf v3 4/6] selftest/bpf: Fix memory leak in kprobe_multi_test

On Mon, Oct 10, 2022 at 7:08 AM Xu Kuohai <xukuohai@...wei.com> wrote:
>
> The get_syms() function in kprobe_multi_test.c does not free the string
> memory allocated by sscanf correctly. Fix it.
>
> Fixes: 5b6c7e5c4434 ("selftests/bpf: Add attach bench test")
> Signed-off-by: Xu Kuohai <xukuohai@...wei.com>
> Acked-by: Jiri Olsa <jolsa@...nel.org>
> ---
>  .../bpf/prog_tests/kprobe_multi_test.c          | 17 ++++++++---------
>  1 file changed, 8 insertions(+), 9 deletions(-)
>
> 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 d457a55ff408..07dd2c5b7f98 100644
> --- a/tools/testing/selftests/bpf/prog_tests/kprobe_multi_test.c
> +++ b/tools/testing/selftests/bpf/prog_tests/kprobe_multi_test.c
> @@ -360,15 +360,14 @@ static int get_syms(char ***symsp, size_t *cntp)
>                  * to them. Filter out the current culprits - arch_cpu_idle
>                  * and rcu_* functions.
>                  */
> -               if (!strcmp(name, "arch_cpu_idle"))
> -                       continue;
> -               if (!strncmp(name, "rcu_", 4))
> -                       continue;
> -               if (!strcmp(name, "bpf_dispatcher_xdp_func"))
> -                       continue;
> -               if (!strncmp(name, "__ftrace_invalid_address__",
> -                            sizeof("__ftrace_invalid_address__") - 1))
> +               if (!strcmp(name, "arch_cpu_idle") ||
> +                       !strncmp(name, "rcu_", 4) ||
> +                       !strcmp(name, "bpf_dispatcher_xdp_func") ||
> +                       !strncmp(name, "__ftrace_invalid_address__",
> +                                sizeof("__ftrace_invalid_address__") - 1)) {
> +                       free(name);
>                         continue;
> +               }

it seems cleaner if we add if (name) free(name) under error: goto
label. And in the success case when we assign name to syms[cnt] we can
reset name to NULL to avoid double-free. WDYT?


>                 err = hashmap__add(map, name, NULL);
>                 if (err) {
>                         free(name);
> @@ -394,7 +393,7 @@ static int get_syms(char ***symsp, size_t *cntp)
>         hashmap__free(map);
>         if (err) {
>                 for (i = 0; i < cnt; i++)
> -                       free(syms[cnt]);
> +                       free(syms[i]);
>                 free(syms);
>         }
>         return err;
> --
> 2.30.2
>