From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35070 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726156AbgIWOkc (ORCPT ); Wed, 23 Sep 2020 10:40:32 -0400 Date: Wed, 23 Sep 2020 15:40:25 +0100 From: Al Viro 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> Sender: Al Viro List-ID: To: Christoph Hellwig Cc: Andrew Morton , Jens Axboe , Arnd Bergmann , David Howells , David Laight , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mips@vger.kernel.org, linux-parisc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, sparclinux@vger.kernel.org, linux-block@vger.kernel.org, linux-scsi@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-aio@kvack.org, io-uring@vger.kernel.org, linux-arch@vger.kernel.org, linux-mm@kvack.org, netdev@vger.kernel.org, keyrings@vger.kernel.org, linux-security-module@vger.kernel.org, Linus Torvalds 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.