linux-kernel - Re: [PATCH] binder: use cred instead of task for selinux checks

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Date:   Fri, 1 Oct 2021 10:44:51 -0400
From:   Paul Moore <paul@...l-moore.com>
To:     Todd Kjos <tkjos@...gle.com>
Cc:     gregkh@...uxfoundation.org, arve@...roid.com, tkjos@...roid.com,
        maco@...roid.com, christian@...uner.io,
        James Morris <jmorris@...ei.org>,
        Serge Hallyn <serge@...lyn.com>,
        Stephen Smalley <stephen.smalley.work@...il.com>,
        Eric Paris <eparis@...isplace.org>, keescook@...omium.org,
        jannh@...gle.com, Jeffrey Vander Stoep <jeffv@...gle.com>,
        zohar@...ux.ibm.com, linux-security-module@...r.kernel.org,
        selinux@...r.kernel.org, devel@...verdev.osuosl.org,
        linux-kernel@...r.kernel.org, joel@...lfernandes.org,
        kernel-team@...roid.com, stable@...r.kernel.org
Subject: Re: [PATCH] binder: use cred instead of task for selinux checks

On Fri, Oct 1, 2021 at 10:38 AM Paul Moore <paul@...l-moore.com> wrote:
> On Thu, Sep 30, 2021 at 10:45 PM Todd Kjos <tkjos@...gle.com> wrote:
> >
> > Save the struct cred associated with a binder process
> > at initial open to avoid potential race conditions
> > when converting to a security ID.
> >
> > Since binder was integrated with selinux, it has passed
> > 'struct task_struct' associated with the binder_proc
> > to represent the source and target of transactions.
> > The conversion of task to SID was then done in the hook
> > implementations. It turns out that there are race conditions
> > which can result in an incorrect security context being used.
> >
> > Fix by saving the 'struct cred' during binder_open and pass
> > it to the selinux subsystem.
> >
> > Fixes: 79af73079d75 ("Add security hooks to binder and implement the
> > hooks for SELinux.")
> > Signed-off-by: Todd Kjos <tkjos@...gle.com>
> > Cc: stable@...r.kernel.org # 5.14 (need backport for earlier stables)
> > ---
> >  drivers/android/binder.c          | 14 +++++----
> >  drivers/android/binder_internal.h |  3 ++
> >  include/linux/lsm_hook_defs.h     | 14 ++++-----
> >  include/linux/security.h          | 28 +++++++++---------
> >  security/security.c               | 14 ++++-----
> >  security/selinux/hooks.c          | 48 +++++++++----------------------
> >  6 files changed, 52 insertions(+), 69 deletions(-)
>
> Thanks Todd, I'm happy to see someone with a better understanding of
> binder than me pitch in to clean this up :)  A couple of quick
> comments/questions below ...

Ooops, I was a little over zealous when trimming my response and I
accidentally cut off my comment that the associated comment blocks in
include/linux/lsm_hooks.h should also be updated to reflect the binder
LSM hook changes.

-- 
paul moore
www.paul-moore.com