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From:   Arnd Bergmann <arnd@arndb.de>
Date:   Fri, 26 Jul 2019 10:19:55 +0200
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Subject: Re: [PATCH 2/5] pidfd: add pidfd_wait()
To:     Christian Brauner <christian@brauner.io>
Cc:     Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Oleg Nesterov <oleg@redhat.com>,
        "Eric W . Biederman" <ebiederm@xmission.com>,
        Kees Cook <keescook@chromium.org>,
        Joel Fernandes <joel@joelfernandes.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Tejun Heo <tj@kernel.org>, David Howells <dhowells@redhat.com>,
        Jann Horn <jannh@google.com>,
        Andy Lutomirski <luto@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Aleksa Sarai <cyphar@cyphar.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Android Kernel Team <kernel-team@android.com>,
        Linux API <linux-api@vger.kernel.org>
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On Wed, Jul 24, 2019 at 4:47 PM Christian Brauner <christian@brauner.io> wrote:

> +
> +static int copy_rusage_to_user_any(struct rusage *kru, struct rusage __user *ru)
> +{
> +#ifdef CONFIG_COMPAT
> +       if (in_compat_syscall())
> +               return put_compat_rusage(kru, (struct compat_rusage __user *)ru);
> +#endif
> +       return copy_to_user(ru, kru, sizeof(*kru));
> +}

I think this code needs a check for COMPAT_USE_64BIT_TIME in order
to handle x32 correctly.

It would be nice to introduce it in a separate patch, and then use it
to kill off
compat_sys_getrusage() and compat_sys_wait4(), and possibly even
compat_sys_waitid() in combination with your copy_siginfo_to_user_any().
That could be done as a cleanup patch afterwards, or as part of your series.

        Arnd