Re: [PATCH v5 3/6] fs: Enable to enforce noexec mounts or file exec through O_MAYEXEC

From: Randy Dunlap <rdunlap@infradead.org>
To: "Mickaël Salaün" <mic@digikod.net>, linux-kernel@vger.kernel.org
Cc: "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>,
	"Deven Bowers" <deven.desai@linux.microsoft.com>,
	"Eric Chiang" <ericchiang@google.com>,
	"Florian Weimer" <fweimer@redhat.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>,
	"Lakshmi Ramasubramanian" <nramas@linux.microsoft.com>,
	"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>,
	"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>,
	kernel-hardening@lists.openwall.com, linux-api@vger.kernel.org,
	linux-integrity@vger.kernel.org,
	linux-security-module@vger.kernel.org,
	linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH v5 3/6] fs: Enable to enforce noexec mounts or file exec through O_MAYEXEC
Date: Tue, 5 May 2020 10:40:31 -0700	[thread overview]
Message-ID: <9e3ec812-128d-cc46-5206-ab72b737b274@infradead.org> (raw)
In-Reply-To: <3555aab7-f4e0-80eb-0dfc-a87cfcba5e68@digikod.net>

On 5/5/20 9:55 AM, Mickaël Salaün wrote:
> 
> 
> On 05/05/2020 17:44, Randy Dunlap wrote:
>> On 5/5/20 8:31 AM, Mickaël Salaün wrote:
>>> diff --git a/security/Kconfig b/security/Kconfig
>>> index cd3cc7da3a55..d8fac9240d14 100644
>>> --- a/security/Kconfig
>>> +++ b/security/Kconfig
>>> @@ -230,6 +230,32 @@ config STATIC_USERMODEHELPER_PATH
>>>  	  If you wish for all usermode helper programs to be disabled,
>>>  	  specify an empty string here (i.e. "").
>>>  
>>> +menuconfig OMAYEXEC_STATIC
>>> +	tristate "Configure O_MAYEXEC behavior at build time"
>>> +	---help---
>>> +	  Enable to enforce O_MAYEXEC at build time, and disable the dedicated
>>> +	  fs.open_mayexec_enforce sysctl.
>>
>> That help message is a bit confusing IMO.  Does setting/enabling OMAYEXEC_STATIC
>> both enforce O_MAYEXEC at build time and also disable the dedicated sysctl?
> 
> Yes. What about this?
> "Define the O_MAYEXEC policy at build time only. As a side effect, this
> also disables the fs.open_mayexec_enforce sysctl."
> 

Yes, much better. Thanks.

>>
>> Or are these meant to be alternatives, one for what Enabling this kconfig symbol
>> does and the other for what Disabling this symbol does?  If so, it doesn't
>> say that.
>>
>>> +
>>> +	  See Documentation/admin-guide/sysctl/fs.rst for more details.
>>> +
>>> +if OMAYEXEC_STATIC
>>> +
>>> +config OMAYEXEC_ENFORCE_MOUNT
>>> +	bool "Mount restriction"
>>> +	default y
>>> +	---help---
>>> +	  Forbid opening files with the O_MAYEXEC option if their underlying VFS is
>>> +	  mounted with the noexec option or if their superblock forbids execution
>>> +	  of its content (e.g., /proc).
>>> +
>>> +config OMAYEXEC_ENFORCE_FILE
>>> +	bool "File permission restriction"
>>> +	---help---
>>> +	  Forbid opening files with the O_MAYEXEC option if they are not marked as
>>> +	  executable for the current process (e.g., POSIX permissions).
>>> +
>>> +endif # OMAYEXEC_STATIC
>>> +
>>>  source "security/selinux/Kconfig"
>>>  source "security/smack/Kconfig"
>>>  source "security/tomoyo/Kconfig"
>>
>>

-- 
~Randy