2021-11-03 07:18:27

by Austin Kim

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

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 <[email protected]>
---
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

2021-11-03 12:15:46

by Mickaël Salaün

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

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 <[email protected]>
> ---
> 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));
>

2021-11-04 11:47:26

by Austin Kim

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

2021년 11월 3일 (수) 오후 9:14, Mickaël Salaün <[email protected]>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 <[email protected]>
> > ---
> > 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));
> >

2021-11-05 18:37:21

by Jay Freyensee

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

On 11/4/21 4:41 AM, Austin Kim wrote:
> 2021년 11월 3일 (수) 오후 9:14, Mickaël Salaün <[email protected]>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 <[email protected]>
>>> ---
>>> 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));
>>>