Date: Mon, 9 Sep 2019 03:12:38 -0700 (PDT) From: James Morris <jmorris@...ei.org> To: Mickaël Salaün <mickael.salaun@....gouv.fr> cc: Jeff Layton <jlayton@...nel.org>, Florian Weimer <fweimer@...hat.com>, Mickaël Salaün <mic@...ikod.net>, linux-kernel@...r.kernel.org, Aleksa Sarai <cyphar@...har.com>, Alexei Starovoitov <ast@...nel.org>, Al Viro <viro@...iv.linux.org.uk>, Andy Lutomirski <luto@...nel.org>, Christian Heimes <christian@...hon.org>, Daniel Borkmann <daniel@...earbox.net>, Eric Chiang <ericchiang@...gle.com>, Jan Kara <jack@...e.cz>, Jann Horn <jannh@...gle.com>, Jonathan Corbet <corbet@....net>, Kees Cook <keescook@...omium.org>, Matthew Garrett <mjg59@...gle.com>, Matthew Wilcox <willy@...radead.org>, Michael Kerrisk <mtk.manpages@...il.com>, Mimi Zohar <zohar@...ux.ibm.com>, Philippe Trébuchet <philippe.trebuchet@....gouv.fr>, Scott Shell <scottsh@...rosoft.com>, Sean Christopherson <sean.j.christopherson@...el.com>, Shuah Khan <shuah@...nel.org>, Song Liu <songliubraving@...com>, Steve Dower <steve.dower@...hon.org>, Steve Grubb <sgrubb@...hat.com>, Thibaut Sautereau <thibaut.sautereau@....gouv.fr>, Vincent Strubel <vincent.strubel@....gouv.fr>, Yves-Alexis Perez <yves-alexis.perez@....gouv.fr>, kernel-hardening@...ts.openwall.com, linux-api@...r.kernel.org, linux-security-module@...r.kernel.org, linux-fsdevel@...r.kernel.org Subject: Re: [PATCH v2 1/5] fs: Add support for an O_MAYEXEC flag on sys_open() On Mon, 9 Sep 2019, Mickaël Salaün wrote: > > On 06/09/2019 21:03, James Morris wrote: > > On Fri, 6 Sep 2019, Jeff Layton wrote: > > > >> The fact that open and openat didn't vet unknown flags is really a bug. > >> > >> Too late to fix it now, of course, and as Aleksa points out, we've > >> worked around that in the past. Now though, we have a new openat2 > >> syscall on the horizon. There's little need to continue these sorts of > >> hacks. > >> > >> New open flags really have no place in the old syscalls, IMO. > > > > Agree here. It's unfortunate but a reality and Linus will reject any such > > changes which break existing userspace. > > Do you mean that adding new flags to open(2) is not possible? > > Does it means that unspecified behaviors are definitely part of the > Linux specification and can't be fixed? This is my understanding. > > As I said, O_MAYEXEC should be ignored if it is not supported by the > kernel, which perfectly fit with the current open(2) flags behavior, and > should also behave the same with openat2(2). The problem here is programs which are already using the value of O_MAYEXEC, which will break. Hence, openat2(2). -- James Morris <jmorris@...ei.org>
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