Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Thu, 5 Sep 2019 13:29:59 +0200
From:   Christian Brauner <christian.brauner@ubuntu.com>
To:     Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc:     Aleksa Sarai <cyphar@cyphar.com>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Jeff Layton <jlayton@kernel.org>,
        "J. Bruce Fields" <bfields@fieldses.org>,
        Arnd Bergmann <arnd@arndb.de>,
        David Howells <dhowells@redhat.com>,
        Shuah Khan <shuah@kernel.org>,
        Shuah Khan <skhan@linuxfoundation.org>,
        Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Christian Brauner <christian@brauner.io>,
        Eric Biederman <ebiederm@xmission.com>,
        Andy Lutomirski <luto@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Alexei Starovoitov <ast@kernel.org>,
        Kees Cook <keescook@chromium.org>,
        Jann Horn <jannh@google.com>, Tycho Andersen <tycho@tycho.ws>,
        David Drysdale <drysdale@google.com>,
        Chanho Min <chanho.min@lge.com>,
        Oleg Nesterov <oleg@redhat.com>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Jiri Olsa <jolsa@redhat.com>,
        Namhyung Kim <namhyung@kernel.org>,
        Aleksa Sarai <asarai@suse.de>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        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: <20190905112958.ldzyzyuqn5akkhzy@wittgenstein>
References: <20190904201933.10736-1-cyphar@cyphar.com>
 <20190904201933.10736-2-cyphar@cyphar.com>
 <20190905110544.d6c5t7rx25kvywmi@wittgenstein>
 <ae415ea8-4442-d81c-3b46-2ae5fb35bbdf@rasmusvillemoes.dk>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
In-Reply-To: <ae415ea8-4442-d81c-3b46-2ae5fb35bbdf@rasmusvillemoes.dk>
User-Agent: NeoMutt/20180716
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Thu, Sep 05, 2019 at 01:17:38PM +0200, Rasmus Villemoes wrote:
> On 05/09/2019 13.05, Christian Brauner wrote:
> > On Thu, Sep 05, 2019 at 06:19:22AM +1000, Aleksa Sarai wrote:
> 
> >> +	if (unlikely(!access_ok(dst, usize)))
> >> +		return -EFAULT;
> >> +
> >> +	/* Deal with trailing bytes. */
> >> +	if (usize < ksize) {
> >> +		if (memchr_inv(src + size, 0, rest))
> >> +			return -EFBIG;
> >> +	} else if (usize > ksize) {
> >> +		if (__memzero_user(dst + size, rest))
> >> +			return -EFAULT;
> > 
> > Is zeroing that memory really our job? Seems to me we should just check
> > it is zeroed.
> 
> Of course it is, otherwise you'd require userspace to clear the output
> buffer it gives us, which in the majority of cases is wasted work. It's
> much easier to reason about if we just say "the kernel populates [uaddr,
> uaddr + usize)".

I don't really mind either way so sure. :)