[PATCH] landlock: Initialize kernel stack variables properly

[PATCH] landlock: Initialize kernel stack variables properly

[Austin Kim]

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));
+
 	/* Copies raw user space buffer, only one type for now. */
 	res = copy_from_user(&path_beneath_attr, rule_attr,
 			sizeof(path_beneath_attr));
-- 
2.20.1

Re: [PATCH] landlock: Initialize kernel stack variables properly

[Mickaël Salaün]

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.

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

Re: [PATCH] landlock: Initialize kernel stack variables properly

[Austin Kim]

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.

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));
> >

Re: [PATCH] landlock: Initialize kernel stack variables properly

[J Freyensee]

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));
>>>