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From:   Joel Savitz <jsavitz@redhat.com>
Date:   Thu, 2 May 2019 17:46:08 -0400
Message-ID: <CAL1p7m6eC3-99oFEyp0F1xn7qN4Vx+s-kHQXh14cMUWoVFqbWw@mail.gmail.com>
Subject: Re: [PATCH v2 1/2] kernel/sys: add PR_GET_TASK_SIZE option to prctl(2)
To:     Cyrill Gorcunov <gorcunov@gmail.com>
Cc:     linux-kernel@vger.kernel.org, Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@kernel.org>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Waiman Long <longman@redhat.com>,
        Mauro Carvalho Chehab <mchehab+samsung@kernel.org>,
        Kristina Martsenko <kristina.martsenko@arm.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Kees Cook <keescook@chromium.org>,
        "Gustavo A. R. Silva" <gustavo@embeddedor.com>,
        YueHaibing <yuehaibing@huawei.com>,
        Micah Morton <mortonm@chromium.org>,
        Yang Shi <yang.shi@linux.alibaba.com>,
        Jann Horn <jannh@google.com>,
        Alexey Dobriyan <adobriyan@gmail.com>,
        Rafael Aquini <aquini@redhat.com>,
        Michael Kerrisk <mtk.manpages@gmail.com>,
        Yury Norov <norov.maillist@gmail.com>
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> 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?