linux-kernel - Re: [PATCH v4 3/3] binder: use euid from cred instead of using task

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Message-ID: <CAHRSSEy=eC0rbHUzDmCo6Na7Ya=uCq7zJ6_cXysi0oWQB=19YQ@mail.gmail.com>
Date:   Fri, 8 Oct 2021 14:24:15 -0700
From:   Todd Kjos <tkjos@...gle.com>
To:     Paul Moore <paul@...l-moore.com>
Cc:     casey@...aufler-ca.com, 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 v4 3/3] binder: use euid from cred instead of using task

On Fri, Oct 8, 2021 at 2:12 PM Paul Moore <paul@...l-moore.com> wrote:
>
> On Wed, Oct 6, 2021 at 8:46 PM Todd Kjos <tkjos@...gle.com> wrote:
> >
> > Set a transaction's sender_euid from the 'struct cred'
> > saved at binder_open() instead of looking up the euid
> > from the binder proc's 'struct task'. This ensures
> > the euid is associated with the security context that
> > of the task that opened binder.
> >
> > Fixes: 457b9a6f09f0 ("Staging: android: add binder driver")
> > Signed-off-by: Todd Kjos <tkjos@...gle.com>
> > Suggested-by: Stephen Smalley <stephen.smalley.work@...il.com>
> > Cc: stable@...r.kernel.org # 4.4+
> > ---
> > v3: added this patch to series
> >
> >  drivers/android/binder.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
>
> This is an interesting ordering of the patches.  Unless I'm missing
> something I would have expected patch 3/3 to come first, followed by
> 2/3, with patch 1/3 at the end; basically the reverse of what was
> posted here.

2/3 and 3/3 both depend on 1/3 (add "cred" member of struct
binder_proc). I kept that in 1/3 to keep that patch the same as what
had already been reviewed. I didn't think much about the ordering
between 2/3 and 3/3 -- but I agree that it would have been sensible to
reverse their order.

>
> My reading of the previous thread was that Casey has made his peace
> with these changes so unless anyone has any objections I'll plan on
> merging 2/3 and 3/3 into selinux/stable-5.15 and merging 1/3 into
> selinux/next.

Thanks Paul. I'm not familiar with the branch structure, but you need
1/3 in selinux/stable-5.15 to resolve the dependency on proc->cred.

>
> > diff --git a/drivers/android/binder.c b/drivers/android/binder.c
> > index 989afd0804ca..26382e982c5e 100644
> > --- a/drivers/android/binder.c
> > +++ b/drivers/android/binder.c
> > @@ -2711,7 +2711,7 @@ static void binder_transaction(struct binder_proc *proc,
> >                 t->from = thread;
> >         else
> >                 t->from = NULL;
> > -       t->sender_euid = task_euid(proc->tsk);
> > +       t->sender_euid = proc->cred->euid;
> >         t->to_proc = target_proc;
> >         t->to_thread = target_thread;
> >         t->code = tr->code;
> > --
> > 2.33.0.800.g4c38ced690-goog
>
> --
> paul moore
> www.paul-moore.com