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References: <20211103071427.GA13854@raspberrypi> <7a71215c-58f4-081b-6a2e-030073f2737e@digikod.net>
In-Reply-To: <7a71215c-58f4-081b-6a2e-030073f2737e@digikod.net>
From:   Austin Kim <austindh.kim@gmail.com>
Date:   Thu, 4 Nov 2021 20:41:10 +0900
Message-ID: <CADLLry4zYn-NZBtC3pdQpb4c_3vvzNfc71rBrXc-oXqgSZNHaQ@mail.gmail.com>
Subject: Re: [PATCH] landlock: Initialize kernel stack variables properly
To:     =?UTF-8?B?TWlja2HDq2wgU2FsYcO8bg==?= <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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2021=EB=85=84 11=EC=9B=94 3=EC=9D=BC (=EC=88=98) =EC=98=A4=ED=9B=84 9:14, M=
icka=C3=ABl Sala=C3=BCn <mic@digikod.net>=EB=8B=98=EC=9D=B4 =EC=9E=91=EC=84=
=B1:
>
> Hi Austin,
>
> On 03/11/2021 08:14, Austin Kim wrote:
> > In case kernel stack variables are not initialized properly, there migh=
t
> > be a little chance of kernel information disclosure. So it is better fo=
r
> > 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 !=3D 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 =3D copy_from_user(&path_beneath_attr, rule_attr,
> >                       sizeof(path_beneath_attr));
> >