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@xxxxxxxxxxx>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@xxxxxxxxx>
> > > ---
> > >   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));