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=-3.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 99F1FC4363D for ; Wed, 23 Sep 2020 14:45:58 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [203.11.71.2]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id A1F72206FB for ; Wed, 23 Sep 2020 14:45:57 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A1F72206FB Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=zeniv.linux.org.uk Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Received: from bilbo.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 4BxLZp6rQjzDqHY for ; Thu, 24 Sep 2020 00:45:54 +1000 (AEST) Authentication-Results: lists.ozlabs.org; spf=none (no SPF record) smtp.mailfrom=ftp.linux.org.uk (client-ip=2002:c35c:fd02::1; helo=zeniv.linux.org.uk; envelope-from=viro@ftp.linux.org.uk; receiver=) Authentication-Results: lists.ozlabs.org; dmarc=none (p=none dis=none) header.from=zeniv.linux.org.uk Received: from ZenIV.linux.org.uk (zeniv.linux.org.uk [IPv6:2002:c35c:fd02::1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 4BxLSj17CWzDq9Z for ; Thu, 24 Sep 2020 00:40:37 +1000 (AEST) Received: from viro by ZenIV.linux.org.uk with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1kL5wX-004avv-5G; Wed, 23 Sep 2020 14:40:25 +0000 Date: Wed, 23 Sep 2020 15:40:25 +0100 From: Al Viro To: Christoph Hellwig Subject: Re: [PATCH 3/9] iov_iter: refactor rw_copy_check_uvector and import_iovec Message-ID: <20200923144025.GL3421308@ZenIV.linux.org.uk> References: <20200923060547.16903-1-hch@lst.de> <20200923060547.16903-4-hch@lst.de> <20200923141654.GJ3421308@ZenIV.linux.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200923141654.GJ3421308@ZenIV.linux.org.uk> X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-aio@kvack.org, linux-mips@vger.kernel.org, David Howells , linux-mm@kvack.org, keyrings@vger.kernel.org, sparclinux@vger.kernel.org, linux-arch@vger.kernel.org, linux-s390@vger.kernel.org, linux-scsi@vger.kernel.org, Linus Torvalds , Arnd Bergmann , linux-block@vger.kernel.org, io-uring@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Jens Axboe , linux-parisc@vger.kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, linux-security-module@vger.kernel.org, David Laight , linux-fsdevel@vger.kernel.org, Andrew Morton , linuxppc-dev@lists.ozlabs.org Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Wed, Sep 23, 2020 at 03:16:54PM +0100, Al Viro wrote: > On Wed, Sep 23, 2020 at 08:05:41AM +0200, Christoph Hellwig wrote: > > > +struct iovec *iovec_from_user(const struct iovec __user *uvec, > > + unsigned long nr_segs, unsigned long fast_segs, > > Hmm... For fast_segs unsigned long had always been ridiculous > (4G struct iovec on caller stack frame?), but that got me wondering about > nr_segs and I wish I'd thought of that when introducing import_iovec(). > > The thing is, import_iovec() takes unsigned int there. Which is fine > (hell, the maximal value that can be accepted in 1024), except that > we do pass unsigned long syscall argument to it in some places. > > E.g. vfs_readv() quietly truncates vlen to 32 bits, and vlen can > come unchanged through sys_readv() -> do_readv() -> vfs_readv(). > With unsigned long passed by syscall glue. > > AFAICS, passing 4G+1 as the third argument to readv(2) on 64bit box > will be quietly treated as 1 these days. Which would be fine, except > that before "switch {compat_,}do_readv_writev() to {compat_,}import_iovec()" > it used to fail with -EINVAL. > > Userland, BTW, describes readv(2) iovcnt as int; process_vm_readv(), > OTOH, has these counts unsigned long from the userland POV... > > I suppose we ought to switch import_iovec() to unsigned long for nr_segs ;-/ > Strictly speaking that had been a userland ABI change, even though nothing > except regression tests checking for expected errors would've been likely > to notice. And it looks like no regression tests covered that one... > > Linus, does that qualify for your "if no userland has noticed the change, > it's not a breakage"? Egads... We have sys_readv() with unsigned long for file descriptor, since 1.3.31 when it had been introduced. And originally it did comparison with NR_OPEN right in sys_readv(). Then in 2.1.60 it had been switched to fget(), which used to take unsigned long at that point. And in 2.1.90pre1 it went unsigned int, so non-zero upper 32 bits in readv(2) first argument ceased to cause EBADF... Of course, libc had it as int fd all along.