linux-kernel - RE: [PATCH v2 1/2] kernel/sys: add PR_GET_TASK

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Date:   Fri, 3 May 2019 11:31:40 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Cyrill Gorcunov' <gorcunov@...il.com>,
        Joel Savitz <jsavitz@...hat.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Thomas Gleixner" <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        "Masami Hiramatsu" <mhiramat@...nel.org>,
        Waiman Long <longman@...hat.com>,
        "Mauro Carvalho Chehab" <mchehab+samsung@...nel.org>,
        Kristina Martsenko <kristina.martsenko@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Kees Cook <keescook@...omium.org>,
        "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
        YueHaibing <yuehaibing@...wei.com>,
        Micah Morton <mortonm@...omium.org>,
        Yang Shi <yang.shi@...ux.alibaba.com>,
        Jann Horn <jannh@...gle.com>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Rafael Aquini <aquini@...hat.com>,
        Michael Kerrisk <mtk.manpages@...il.com>,
        Yury Norov <norov.maillist@...il.com>
Subject: RE: [PATCH v2 1/2] kernel/sys: add PR_GET_TASK_SIZE option to
 prctl(2)

From: Cyrill Gorcunov
> Sent: 03 May 2019 09:32
> On Thu, May 02, 2019 at 05:46:08PM -0400, Joel Savitz wrote:
> > > Won't be possible to use put_user here? Something like
> > >
> > > static int prctl_get_tasksize(unsigned long __user *uaddr)
> > > {
> > >         return put_user(TASK_SIZE, uaddr) ? -EFAULT : 0;
> > > }
> >
> > What would be the benefit of using put_user() over copy_to_user() in
> > this context?
> 
> It is a common pattern to use put_user with native types, where
> copy_to_user more biased for composed types transfer.

It also removes all the crappy code that checks whether the
kernel buffer is valid.

	David

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