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

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Message-ID: <2c6203ac-de2a-607e-0589-0a69f91e0479@iogearbox.net>
Date:   Tue, 1 Nov 2022 14:46:54 +0100
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Bill Wendling <morbo@...gle.com>, Kees Cook <keescook@...omium.org>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        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,
        Zhengchao Shao <shaozhengchao@...wei.com>,
        Lorenz Bauer <oss@....io>
Subject: Re: [PATCH bpf-next v2 1/3] bpf/verifier: Fix potential memory leak
 in array reallocation

[ +Lorenz ]

On 10/31/22 9:16 PM, Bill Wendling wrote:
> 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;

Fyi, I took this fix into bpf tree and improved commit log a bit with the
one from Zhengchao [0] given yours came in first. Fixes tag would have been
nice, I added the c69431aab67a to the commit message while applying.

   [0] https://patchwork.kernel.org/project/netdevbpf/patch/20221031070812.339883-1-shaozhengchao@huawei.com/

>>          if (new_n > old_n)
>>                  memset(arr + old_n * size, 0, (new_n - old_n) * size);
>> --
>> 2.34.1
>>