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Date:   Fri, 5 Nov 2021 09:58:47 -0700
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Subject: Re: [PATCH] landlock: Initialize kernel stack variables properly
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To:     Austin Kim <austindh.kim@gmail.com>,
        =?UTF-8?Q?Micka=c3=abl_Sala=c3=bcn?= <mic@digikod.net>
Cc:     "Serge E. Hallyn" <serge@hallyn.com>,
        linux-security-module <linux-security-module@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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 <CADLLry4zYn-NZBtC3pdQpb4c_3vvzNfc71rBrXc-oXqgSZNHaQ@mail.gmail.com>
From:   J Freyensee <why2jjj.linux@gmail.com>
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On 11/4/21 4:41 AM, Austin Kim wrote:
> 2021년 11월 3일 (수) 오후 9:14, Mickaël Salaün <mic@digikod.net>님이 작성:
>> Hi Austin,
>>
>> On 03/11/2021 08:14, Austin Kim wrote:
>>> In case kernel stack variables are not initialized properly, there might
>>> be a little chance of kernel information disclosure. So it is better for
>>> kernel stack variables to be initialized with null characters.
>>>
>>> Signed-off-by: Austin Kim <austindh.kim@gmail.com>
>>> ---
>>>   security/landlock/syscalls.c | 2 ++
>>>   1 file changed, 2 insertions(+)
>>>
>>> diff --git a/security/landlock/syscalls.c b/security/landlock/syscalls.c
>>> index 32396962f04d..50a6f7091428 100644
>>> --- a/security/landlock/syscalls.c
>>> +++ b/security/landlock/syscalls.c
>>> @@ -320,6 +320,8 @@ SYSCALL_DEFINE4(landlock_add_rule,
>>>        if (rule_type != LANDLOCK_RULE_PATH_BENEATH)
>>>                return -EINVAL;
>>>
>>> +     memset(&path_beneath_attr, 0, sizeof(path_beneath_attr));
>>> +
>> This memset is already done with the copy_from_user() call just below.
>>
> It seems that memset() is done inside copy_from_user().
> Thanks for feedback.

If you are really sensitive of what information may be disclosed in this 
case you can consider memzero_explicit() to use instead:

https://www.kernel.org/doc/htmldocs/kernel-api/API-memzero-explicit.html

Jay

>
> BR,
> Austin Kim
>
>>>        /* Copies raw user space buffer, only one type for now. */
>>>        res = copy_from_user(&path_beneath_attr, rule_attr,
>>>                        sizeof(path_beneath_attr));
>>>