linux-kernel - RE: [RFC v3 7/8] binder: use __kernel_pid_t and __kernel_uid

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Date:   Tue, 15 Mar 2022 07:56:26 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     "'T.J. Mercier'" <tjmercier@...gle.com>,
        Todd Kjos <tkjos@...gle.com>
CC:     Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Jonathan Corbet <corbet@....net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Arve Hjønnevåg <arve@...roid.com>,
        Todd Kjos <tkjos@...roid.com>,
        Martijn Coenen <maco@...roid.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Christian Brauner <brauner@...nel.org>,
        "Hridya Valsaraju" <hridya@...gle.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        "Sumit Semwal" <sumit.semwal@...aro.org>,
        Christian König <christian.koenig@....com>,
        Benjamin Gaignard <benjamin.gaignard@...aro.org>,
        Liam Mark <lmark@...eaurora.org>,
        Laura Abbott <labbott@...hat.com>,
        "Brian Starkey" <Brian.Starkey@....com>,
        John Stultz <john.stultz@...aro.org>,
        "Tejun Heo" <tj@...nel.org>, Zefan Li <lizefan.x@...edance.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Shuah Khan <shuah@...nel.org>,
        Kalesh Singh <kaleshsingh@...gle.com>,
        "Kenny.Ho@....com" <Kenny.Ho@....com>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-media@...r.kernel.org" <linux-media@...r.kernel.org>,
        "linaro-mm-sig@...ts.linaro.org" <linaro-mm-sig@...ts.linaro.org>,
        "cgroups@...r.kernel.org" <cgroups@...r.kernel.org>,
        "linux-kselftest@...r.kernel.org" <linux-kselftest@...r.kernel.org>
Subject: RE: [RFC v3 7/8] binder: use __kernel_pid_t and __kernel_uid_t for
 userspace

From: T.J. Mercier
> Sent: 14 March 2022 23:45
> 
> On Thu, Mar 10, 2022 at 11:33 AM Todd Kjos <tkjos@...gle.com> wrote:
> >
> > On Wed, Mar 9, 2022 at 8:52 AM T.J. Mercier <tjmercier@...gle.com> wrote:
> > >
> > > The kernel interface should use types that the kernel defines instead of
> > > pid_t and uid_t, whose definiton is owned by libc. This fixes the header
> > > so that it can be included without first including sys/types.h.
> > >
> > > Signed-off-by: T.J. Mercier <tjmercier@...gle.com>
> > > ---
> > >  include/uapi/linux/android/binder.h | 4 ++--
> > >  1 file changed, 2 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/include/uapi/linux/android/binder.h b/include/uapi/linux/android/binder.h
> > > index 169fd5069a1a..aa28454dbca3 100644
> > > --- a/include/uapi/linux/android/binder.h
> > > +++ b/include/uapi/linux/android/binder.h
> > > @@ -289,8 +289,8 @@ struct binder_transaction_data {
> > >
> > >         /* General information about the transaction. */
> > >         __u32           flags;
> > > -       pid_t           sender_pid;
> > > -       uid_t           sender_euid;
> > > +       __kernel_pid_t  sender_pid;
> > > +       __kernel_uid_t  sender_euid;
> >
> > Are we guaranteed that this does not affect the UAPI at all? Userspace
> > code using this definition will have to run with kernels using the old
> > definition and visa-versa.
> 
> A standards compliant userspace should be expecting a signed integer
> type here. So the only way I can think userspace would be affected is
> if:
> 1) pid_t is a long AND
> 2) sizeof(long) > sizeof(int) AND
> 3) Consumers of the pid_t definition actually attempt to mutate the
> result to make use of extra bits in the variable (which are not there)

Or the userspace headers have a 16bit pid_t.

I can't help feeling that uapi headers should only use explicit
fixed sized types.
There is no point indirecting the type names - the sizes still
can't be changes.

	David

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