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From: Aleksa Sarai <cyphar@cyphar.com>
To: "Mickaël Salaün" <mickael.salaun@ssi.gouv.fr>
Cc: "Florian Weimer" <fweimer@redhat.com>,
	"Mickaël Salaün" <mic@digikod.net>,
	linux-kernel@vger.kernel.org,
	"Alexei Starovoitov" <ast@kernel.org>,
	"Al Viro" <viro@zeniv.linux.org.uk>,
	"Andy Lutomirski" <luto@kernel.org>,
	"Christian Heimes" <christian@python.org>,
	"Daniel Borkmann" <daniel@iogearbox.net>,
	"Eric Chiang" <ericchiang@google.com>,
	"James Morris" <jmorris@namei.org>, "Jan Kara" <jack@suse.cz>,
	"Jann Horn" <jannh@google.com>,
	"Jonathan Corbet" <corbet@lwn.net>,
	"Kees Cook" <keescook@chromium.org>,
	"Matthew Garrett" <mjg59@google.com>,
	"Matthew Wilcox" <willy@infradead.org>,
	"Michael Kerrisk" <mtk.manpages@gmail.com>,
	"Mimi Zohar" <zohar@linux.ibm.com>,
	"Philippe Trébuchet" <philippe.trebuchet@ssi.gouv.fr>,
	"Scott Shell" <scottsh@microsoft.com>,
	"Sean Christopherson" <sean.j.christopherson@intel.com>,
	"Shuah Khan" <shuah@kernel.org>,
	"Song Liu" <songliubraving@fb.com>,
	"Steve Dower" <steve.dower@python.org>,
	"Steve Grubb" <sgrubb@redhat.com>,
	"Thibaut Sautereau" <thibaut.sautereau@ssi.gouv.fr>,
	"Vincent Strubel" <vincent.strubel@ssi.gouv.fr>,
	"Yves-Alexis Perez" <yves-alexis.perez@ssi.gouv.fr>,
	kernel-hardening@lists.openwall.com, linux-api@vger.kernel.org,
	linux-security-module@vger.kernel.org,
	linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH v2 1/5] fs: Add support for an O_MAYEXEC flag on sys_open()
Date: Sat, 7 Sep 2019 03:07:39 +1000	[thread overview]
Message-ID: <20190906170739.kk3opr2phidb7ilb@yavin.dot.cyphar.com> (raw)
In-Reply-To: <75442f3b-a3d8-12db-579a-2c5983426b4d@ssi.gouv.fr>

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On 2019-09-06, Mickaël Salaün <mickael.salaun@ssi.gouv.fr> wrote:
> 
> On 06/09/2019 17:56, Florian Weimer wrote:
> > Let's assume I want to add support for this to the glibc dynamic loader,
> > while still being able to run on older kernels.
> >
> > Is it safe to try the open call first, with O_MAYEXEC, and if that fails
> > with EINVAL, try again without O_MAYEXEC?
> 
> The kernel ignore unknown open(2) flags, so yes, it is safe even for
> older kernel to use O_MAYEXEC.

Depends on your definition of "safe" -- a security feature that you will
silently not enable on older kernels doesn't sound super safe to me.
Unfortunately this is a limitation of open(2) that we cannot change --
which is why the openat2(2) proposal I've been posting gives -EINVAL for
unknown O_* flags.

There is a way to probe for support (though unpleasant), by creating a
test O_MAYEXEC fd and then checking if the flag is present in
/proc/self/fdinfo/$n.

-- 
Aleksa Sarai
Senior Software Engineer (Containers)
SUSE Linux GmbH
<https://www.cyphar.com/>

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  parent reply	other threads:[~2019-09-06 17:08 UTC|newest]

Thread overview: 45+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-09-06 15:24 [PATCH v2 0/5] Add support for O_MAYEXEC Mickaël Salaün
2019-09-06 15:24 ` [PATCH v2 1/5] fs: Add support for an O_MAYEXEC flag on sys_open() Mickaël Salaün
2019-09-06 15:56   ` Florian Weimer
2019-09-06 16:06     ` Mickaël Salaün
2019-09-06 16:48       ` Jeff Layton
2019-09-06 17:13         ` Aleksa Sarai
2019-09-06 19:43           ` Jeff Layton
2019-09-06 20:06             ` Andy Lutomirski
2019-09-06 20:51               ` Jeff Layton
2019-09-06 21:27                 ` Andy Lutomirski
2019-09-06 22:12                 ` Aleksa Sarai
2019-09-09  9:33               ` Mickaël Salaün
2019-09-06 22:05             ` Aleksa Sarai
2019-09-06 22:18               ` Aleksa Sarai
2019-09-06 17:14         ` Mickaël Salaün
2019-09-06 18:38           ` Jeff Layton
2019-09-06 18:41             ` Andy Lutomirski
2019-09-09  9:18               ` Mickaël Salaün
2019-09-09 15:49                 ` Andy Lutomirski
2019-09-06 18:44             ` Florian Weimer
2019-09-06 19:03             ` James Morris
2019-09-09  9:25               ` Mickaël Salaün
2019-09-09 10:12                 ` James Morris
2019-09-09 10:54                   ` Mickaël Salaün
2019-09-09 12:28                     ` Aleksa Sarai
2019-09-09 12:33                       ` Mickaël Salaün
2019-09-09 11:54                 ` Aleksa Sarai
2019-09-09 12:28                   ` Mickaël Salaün
2019-09-06 17:07       ` Aleksa Sarai [this message]
2019-09-06 17:20         ` Christian Brauner
2019-09-06 17:24           ` Mickaël Salaün
2019-09-06 17:40           ` Tycho Andersen
2019-09-06 18:27             ` Florian Weimer
2019-09-06 18:46               ` Tycho Andersen
2019-09-06 15:24 ` [PATCH v2 2/5] fs: Add a MAY_EXECMOUNT flag to infer the noexec mount propertie Mickaël Salaün
2019-09-06 15:24 ` [PATCH v2 3/5] fs: Enable to enforce noexec mounts or file exec through O_MAYEXEC Mickaël Salaün
2019-09-06 15:24 ` [PATCH v2 4/5] selftest/exec: Add tests for O_MAYEXEC enforcing Mickaël Salaün
2019-09-06 15:24 ` [PATCH v2 5/5] doc: Add documentation for the fs.open_mayexec_enforce sysctl Mickaël Salaün
2019-09-06 18:50 ` [PATCH v2 0/5] Add support for O_MAYEXEC Steve Grubb
2019-09-06 18:57   ` Florian Weimer
2019-09-06 19:07     ` Steve Grubb
2019-09-06 19:26       ` Andy Lutomirski
2019-09-06 22:44         ` Aleksa Sarai
2019-09-09  9:09           ` Mickaël Salaün
2019-09-09  0:16 ` James Morris

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