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From: Steve Grubb <sgrubb@redhat.com>
To: Florian Weimer <fweimer@redhat.com>
Cc: "Mickaël Salaün" <mic@digikod.net>,
	linux-kernel@vger.kernel.org, "Aleksa Sarai" <cyphar@cyphar.com>,
	"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>,
	"Mickaël Salaün" <mickael.salaun@ssi.gouv.fr>,
	"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>,
	"Thibaut S autereau" <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 0/5] Add support for O_MAYEXEC
Date: Fri, 06 Sep 2019 15:07:19 -0400
Message-ID: <1802966.yheqmZt8Si@x2> (raw)
In-Reply-To: <87mufhckxv.fsf@oldenburg2.str.redhat.com>

On Friday, September 6, 2019 2:57:00 PM EDT Florian Weimer wrote:
> * Steve Grubb:
> > Now with LD_AUDIT
> > $ LD_AUDIT=/home/sgrubb/test/openflags/strip-flags.so.0 strace ./test
> > 2>&1 | grep passwd openat(3, "passwd", O_RDONLY)           = 4
> > 
> > No O_CLOEXEC flag.
> 
> I think you need to explain in detail why you consider this a problem.

Because you can strip the O_MAYEXEC flag from being passed into the kernel. 
Once you do that, you defeat the security mechanism because it never gets 
invoked. The issue is that the only thing that knows _why_ something is being 
opened is user space. With this mechanism, you can attempt to pass this 
reason to the kernel so that it may see if policy permits this. But you can 
just remove the flag.

-Steve

> With LD_PRELOAD and LD_AUDIT, you can already do anything, including
> scanning other loaded objects for a system call instruction and jumping
> to that (in case a security module in the kernel performs a PC check to
> confer additional privileges).
> 
> Thanks,
> Florian





  reply index

Thread overview: 45+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-09-06 15:24 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
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 [this message]
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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