From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 72A37C43331 for ; Thu, 5 Sep 2019 18:23:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6F62520825 for ; Thu, 5 Sep 2019 18:23:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389368AbfIESXm (ORCPT ); Thu, 5 Sep 2019 14:23:42 -0400 Received: from youngberry.canonical.com ([91.189.89.112]:43028 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727764AbfIESXl (ORCPT ); Thu, 5 Sep 2019 14:23:41 -0400 Received: from [213.220.153.21] (helo=wittgenstein) by youngberry.canonical.com with esmtpsa (TLS1.0:RSA_AES_256_CBC_SHA1:32) (Exim 4.76) (envelope-from ) id 1i5wPR-00053t-Nn; Thu, 05 Sep 2019 18:23:05 +0000 Date: Thu, 5 Sep 2019 20:23:03 +0200 From: Christian Brauner To: Al Viro Cc: Aleksa Sarai , Jeff Layton , "J. Bruce Fields" , Arnd Bergmann , David Howells , Shuah Khan , Shuah Khan , Ingo Molnar , Peter Zijlstra , Christian Brauner , Rasmus Villemoes , Eric Biederman , Andy Lutomirski , Andrew Morton , Alexei Starovoitov , Kees Cook , Jann Horn , Tycho Andersen , David Drysdale , Chanho Min , Oleg Nesterov , Alexander Shishkin , Jiri Olsa , Namhyung Kim , Aleksa Sarai , Linus Torvalds , containers@lists.linux-foundation.org, linux-alpha@vger.kernel.org, linux-api@vger.kernel.org, linux-arch@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-fsdevel@vger.kernel.org, linux-ia64@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-m68k@lists.linux-m68k.org, linux-mips@vger.kernel.org, linux-parisc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, linux-sh@vger.kernel.org, linux-xtensa@linux-xtensa.org, sparclinux@vger.kernel.org Subject: Re: [PATCH v12 01/12] lib: introduce copy_struct_{to,from}_user helpers Message-ID: <20190905182303.7f6bxpa2enbgcegv@wittgenstein> References: <20190904201933.10736-1-cyphar@cyphar.com> <20190904201933.10736-2-cyphar@cyphar.com> <20190905180750.GQ1131@ZenIV.linux.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20190905180750.GQ1131@ZenIV.linux.org.uk> User-Agent: NeoMutt/20180716 Sender: linux-kselftest-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kselftest@vger.kernel.org On Thu, Sep 05, 2019 at 07:07:50PM +0100, Al Viro wrote: > On Thu, Sep 05, 2019 at 06:19:22AM +1000, Aleksa Sarai wrote: > > +/* > > + * "memset(p, 0, size)" but for user space buffers. Caller must have already > > + * checked access_ok(p, size). > > + */ > > +static int __memzero_user(void __user *p, size_t s) > > +{ > > + const char zeros[BUFFER_SIZE] = {}; > > + while (s > 0) { > > + size_t n = min(s, sizeof(zeros)); > > + > > + if (__copy_to_user(p, zeros, n)) > > + return -EFAULT; > > + > > + p += n; > > + s -= n; > > + } > > + return 0; > > +} > > That's called clear_user(). > > > +int copy_struct_to_user(void __user *dst, size_t usize, > > + const void *src, size_t ksize) > > +{ > > + size_t size = min(ksize, usize); > > + size_t rest = abs(ksize - usize); > > + > > + if (unlikely(usize > PAGE_SIZE)) > > + return -EFAULT; > > Why? Because every caller of that function right now has that limit set anyway iirc. So we can either remove it from here and place it back for the individual callers or leave it in the helper. Also, I'm really asking, why not? Is it unreasonable to have an upper bound on the size (for a long time probably) or are you disagreeing with PAGE_SIZE being used? PAGE_SIZE limit is currently used by sched, perf, bpf, and clone3 and in a few other places.