From: Al Viro Subject: Re: [RFC] situation with csum_and_copy_... API Date: Tue, 18 Nov 2014 21:23:07 +0000 Message-ID: <20141118212307.GU7996@ZenIV.linux.org.uk> References: <20141118084745.GT7996@ZenIV.linux.org.uk> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Network Development , David Miller , Linux Kernel Mailing List To: Linus Torvalds Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Tue, Nov 18, 2014 at 12:49:13PM -0800, Linus Torvalds wrote: > On Tue, Nov 18, 2014 at 12:47 AM, Al Viro wrote: > > The minimal implementations would be > > > > __wsum csum_and_copy_from_user(const void __user *src, void *dst, int len, > > __wsum sum, int *err_ptr) > > { > > if (unlikely(copy_from_user(dst, src, len) < 0)) { > > No. That "< 0" should be "!= 0". The user copy functions return a > positive value of how many bytes they *failed* to copy. D'oh... Yes, indeed - sorry about the braino. > > IMO the calling conventions are atrocious. > > Yeah, not pretty. At the same time, the pain of changing what seems to > work might not be worth it. > > And quite frankly, I *detest* your patch 3/5. > > "access_ok()" isn't that expensive, and removing them as unnecessary > is fraught with errors. We've had several cases of "oops, we used > __get_user() in a loop, because it generates much better code, but > we'd forgotten to do access_ok(), so now people can read kernel data". OK... If netdev folks can live with that for now, I've no problem with dropping 3/5. However, I really think we need a variant of csum-and-copy that would _not_ bother with access_ok() longer term. That can wait, though...