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Subject: Re: [PATCH v5 3/6] fs: Enable to enforce noexec mounts or file exec
 through O_MAYEXEC
To:     Randy Dunlap <rdunlap@infradead.org>, 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>,
        =?UTF-8?Q?Micka=c3=abl_Sala=c3=bcn?= <mickael.salaun@ssi.gouv.fr>,
        Mimi Zohar <zohar@linux.ibm.com>,
        =?UTF-8?Q?Philippe_Tr=c3=a9buchet?= 
        <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
References: <20200505153156.925111-1-mic@digikod.net>
 <20200505153156.925111-4-mic@digikod.net>
 <fb6e2d7d-a372-3e79-214d-3ac9a451cd0a@infradead.org>
From:   =?UTF-8?Q?Micka=c3=abl_Sala=c3=bcn?= <mic@digikod.net>
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Date:   Tue, 5 May 2020 18:55:59 +0200
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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."

> 
> 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"
> 
>