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

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Message-ID: <CAHRSSEwYrqFum7gS0XOYG0p3F+0Hv8qvaZbWLUyXUm0oCWpX9w@mail.gmail.com>
Date:   Mon, 11 Oct 2021 16:39:45 -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 Mon, Oct 11, 2021 at 2:39 PM Paul Moore <paul@...l-moore.com> wrote:
>
> On Fri, Oct 8, 2021 at 5:24 PM Todd Kjos <tkjos@...gle.com> wrote:
> >
> > 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.
>
> Yep, thanks.  My eyes kinda skipped over that part when looking at the
> patchset but that would have fallen out as soon as I merged them.
>
> Unfortunately that pretty much defeats the purpose of splitting this
> into three patches.  While I suppose one could backport patches 2/3
> and 3/3 individually, both of them have a very small footprint
> especially considering their patch 1/3 dependency.  At the very least
> it looks like patch 2/3 needs to be respun to address the
> !CONFIG_SECURITY case and seeing the split patches now I think the
> smart thing is to just combine them into a single patch.  I apologize
> for the bad recommendation earlier, I should have followed that thread
> a bit closer after the discussion with Casey and Stephen.

I'm happy to submit a single patch for all of this. Another part of
the rationale
for splitting it into 3 patches was correctly identify the patch that introduced
the patch that introduced the issue -- so each of the 3 had a different
"Fixes:" tag. Should I cite the oldest (binder introduction) with the "Fixes"
tag and perhaps mention the other two in the commit message?

-Todd

>
> --
> paul moore
> www.paul-moore.com