Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754571AbbLKWS2 (ORCPT ); Fri, 11 Dec 2015 17:18:28 -0500 Received: from terminus.zytor.com ([198.137.202.10]:51482 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754162AbbLKWS0 (ORCPT ); Fri, 11 Dec 2015 17:18:26 -0500 Subject: Re: [PATCH] devpts: Sensible /dev/ptmx & force newinstance To: Andy Lutomirski , "Eric W. Biederman" References: <1CB621EF-1647-463B-A144-D611DB150E15@zytor.com> <20151208223135.GA8352@kroah.com> <87oae0h2bo.fsf@x220.int.ebiederm.org> <56677DE3.5040705@zytor.com> <20151209012311.GA11794@kroah.com> <84B136DF-55E4-476A-9CB2-062B15677EE5@zytor.com> <20151209013859.GA12442@kroah.com> <20151209083225.GA30452@1wt.eu> <87wpskyds7.fsf_-_@x220.int.ebiederm.org> <20151211210400.GL20997@ZenIV.linux.org.uk> <87h9jovgf7.fsf@x220.int.ebiederm.org> Cc: Al Viro , Greg KH , Jiri Slaby , Linus Torvalds , Aurelien Jarno , Florian Weimer , Serge Hallyn , Jann Horn , "security@kernel.org" , "security@ubuntu.com >> security" , security@debian.org, Willy Tarreau , "linux-kernel@vger.kernel.org" From: "H. Peter Anvin" X-Enigmail-Draft-Status: N1110 Message-ID: <566B4931.5080806@zytor.com> Date: Fri, 11 Dec 2015 14:07:45 -0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.3.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1376 Lines: 36 On 12/11/15 13:48, Andy Lutomirski wrote: > On Fri, Dec 11, 2015 at 1:11 PM, Eric W. Biederman > wrote: >> Al Viro writes: >> >>> On Fri, Dec 11, 2015 at 01:40:40PM -0600, Eric W. Biederman wrote: >>> >>>> + inode = path.dentry->d_inode; >>>> + filp->f_path = path; >>>> + filp->f_inode = inode; >>>> + filp->f_mapping = inode->i_mapping; >>>> + path_put(&old); >>> >>> Don't. You are creating a fairly subtle constraint on what the code in >>> fs/open.c and fs/namei.c can do, for no good reason. You can bloody >>> well maintain the information you need without that. >> >> There is a good reason. We can not write a race free version of ptsname >> without it. > > As long as this is for new userspace code, would it make sense to just > add a new ioctl to ask "does this ptmx fd match this /dev/pts fd?" > For the newinstance case st_dev should match between the master and the slave. Unfortunately this is not the case for a legacy ptmx, as a stat() on the master descriptor still returns the st_dev, st_rdev, and st_ino for the ptmx device node. -hpa -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/