linux-hardening - Re: [PATCH bpf-next v2 1/3] bpf/verifier: Fix potential memory leak in array reallocation

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Message-ID: <CAGG=3QXYVwQ5pwARdGTenm-mDQn4Tcz6U-=EZ8BDcwBkM5bFfg@mail.gmail.com>
Date:   Mon, 31 Oct 2022 13:16:09 -0700
From:   Bill Wendling <morbo@...gle.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        John Fastabend <john.fastabend@...il.com>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Song Liu <song@...nel.org>, Yonghong Song <yhs@...com>,
        KP Singh <kpsingh@...nel.org>,
        Stanislav Fomichev <sdf@...gle.com>,
        Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
        bpf@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-hardening@...r.kernel.org
Subject: Re: [PATCH bpf-next v2 1/3] bpf/verifier: Fix potential memory leak
 in array reallocation

On Fri, Oct 28, 2022 at 7:55 PM Kees Cook <keescook@...omium.org> wrote:
>
> If an error (NULL) is returned by krealloc(), callers of realloc_array()
> were setting their allocation pointers to NULL, but on error krealloc()
> does not touch the original allocation. This would result in a memory
> resource leak. Instead, free the old allocation on the error handling
> path.
>
> Cc: Alexei Starovoitov <ast@...nel.org>
> Cc: Daniel Borkmann <daniel@...earbox.net>
> Cc: John Fastabend <john.fastabend@...il.com>
> Cc: Andrii Nakryiko <andrii@...nel.org>
> Cc: Martin KaFai Lau <martin.lau@...ux.dev>
> Cc: Song Liu <song@...nel.org>
> Cc: Yonghong Song <yhs@...com>
> Cc: KP Singh <kpsingh@...nel.org>
> Cc: Stanislav Fomichev <sdf@...gle.com>
> Cc: Hao Luo <haoluo@...gle.com>
> Cc: Jiri Olsa <jolsa@...nel.org>
> Cc: bpf@...r.kernel.org
> Signed-off-by: Kees Cook <keescook@...omium.org>

Reviewed-by: Bill Wendling <morbo@...gle.com>

> ---
>  kernel/bpf/verifier.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 014ee0953dbd..eb8c34db74c7 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -1027,12 +1027,17 @@ static void *copy_array(void *dst, const void *src, size_t n, size_t size, gfp_t
>   */
>  static void *realloc_array(void *arr, size_t old_n, size_t new_n, size_t size)
>  {
> +       void *new_arr;
> +
>         if (!new_n || old_n == new_n)
>                 goto out;
>
> -       arr = krealloc_array(arr, new_n, size, GFP_KERNEL);
> -       if (!arr)
> +       new_arr = krealloc_array(arr, new_n, size, GFP_KERNEL);
> +       if (!new_arr) {
> +               kfree(arr);
>                 return NULL;
> +       }
> +       arr = new_arr;
>
>         if (new_n > old_n)
>                 memset(arr + old_n * size, 0, (new_n - old_n) * size);
> --
> 2.34.1
>