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From: "Mickaël Salaün" <mic@digikod.net>
To: Kees Cook <keescook@chromium.org>,
	Stephen Smalley <stephen.smalley.work@gmail.com>
Cc: linux-kernel <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>,
	"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>,
	"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,
	"LSM List" <linux-security-module@vger.kernel.org>,
	"Linux FS Devel" <linux-fsdevel@vger.kernel.org>
Subject: Re: [PATCH v5 3/6] fs: Enable to enforce noexec mounts or file exec through O_MAYEXEC
Date: Thu, 14 May 2020 21:21:21 +0200
Message-ID: <0e654c90-bec5-6ba1-771e-648da94ef547@digikod.net> (raw)
In-Reply-To: <202005131525.D08BFB3@keescook>



On 14/05/2020 01:27, Kees Cook wrote:
> On Wed, May 13, 2020 at 11:37:16AM -0400, Stephen Smalley wrote:
>> On Tue, May 5, 2020 at 11:33 AM Mickaël Salaün <mic@digikod.net> wrote:
>>>
>>> Enable to forbid access to files open with O_MAYEXEC.  Thanks to the
>>> noexec option from the underlying VFS mount, or to the file execute
>>> permission, userspace can enforce these execution policies.  This may
>>> allow script interpreters to check execution permission before reading
>>> commands from a file, or dynamic linkers to allow shared object loading.
>>>
>>> Add a new sysctl fs.open_mayexec_enforce to enable system administrators
>>> to enforce two complementary security policies according to the
>>> installed system: enforce the noexec mount option, and enforce
>>> executable file permission.  Indeed, because of compatibility with
>>> installed systems, only system administrators are able to check that
>>> this new enforcement is in line with the system mount points and file
>>> permissions.  A following patch adds documentation.
>>>
>>> For tailored Linux distributions, it is possible to enforce such
>>> restriction at build time thanks to the CONFIG_OMAYEXEC_STATIC option.
>>> The policy can then be configured with CONFIG_OMAYEXEC_ENFORCE_MOUNT and
>>> CONFIG_OMAYEXEC_ENFORCE_FILE.
>>>
>>> Being able to restrict execution also enables to protect the kernel by
>>> restricting arbitrary syscalls that an attacker could perform with a
>>> crafted binary or certain script languages.  It also improves multilevel
>>> isolation by reducing the ability of an attacker to use side channels
>>> with specific code.  These restrictions can natively be enforced for ELF
>>> binaries (with the noexec mount option) but require this kernel
>>> extension to properly handle scripts (e.g., Python, Perl).  To get a
>>> consistent execution policy, additional memory restrictions should also
>>> be enforced (e.g. thanks to SELinux).
>>>
>>> Signed-off-by: Mickaël Salaün <mic@digikod.net>
>>> Reviewed-by: Thibaut Sautereau <thibaut.sautereau@ssi.gouv.fr>
>>> Cc: Aleksa Sarai <cyphar@cyphar.com>
>>> Cc: Al Viro <viro@zeniv.linux.org.uk>
>>> Cc: Kees Cook <keescook@chromium.org>
>>> ---
>>
>>> diff --git a/fs/namei.c b/fs/namei.c
>>> index 33b6d372e74a..70f179f6bc6c 100644
>>> --- a/fs/namei.c
>>> +++ b/fs/namei.c
>>> @@ -411,10 +412,90 @@ static int sb_permission(struct super_block *sb, struct inode *inode, int mask)
>> <snip>
>>> +#if defined(CONFIG_SYSCTL) && !defined(CONFIG_OMAYEXEC_STATIC)
>>> +int proc_omayexec(struct ctl_table *table, int write, void __user *buffer,
>>> +               size_t *lenp, loff_t *ppos)
>>> +{
>>> +       int error;
>>> +
>>> +       if (write) {
>>> +               struct ctl_table table_copy;
>>> +               int tmp_mayexec_enforce;
>>> +
>>> +               if (!capable(CAP_MAC_ADMIN))
>>> +                       return -EPERM;
>>
>> Not fond of using CAP_MAC_ADMIN here (or elsewhere outside of security
>> modules).  The ability to set this sysctl is not equivalent to being
>> able to load a MAC policy, set arbitrary MAC labels on
>> processes/files, etc.
> 
> That's fair. In that case, perhaps this could just use the existing
> _sysadmin helper? (Though I should note that these perm checks actually
> need to be in the open, not the read/write ... I thought there was a
> series to fix that, but I can't find it now. Regardless, that's
> orthogonal to this series.)

OK, I'll switch to CAP_SYS_ADMIN with proc_dointvec_minmax_sysadmin().

  parent reply index

Thread overview: 59+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-05 15:31 [PATCH v5 0/6] Add support for O_MAYEXEC Mickaël Salaün
2020-05-05 15:31 ` [PATCH v5 1/6] fs: Add support for an O_MAYEXEC flag on openat2(2) Mickaël Salaün
2020-05-12 21:05   ` Kees Cook
2020-05-12 21:40     ` Christian Heimes
2020-05-12 22:56       ` Kees Cook
2020-05-13 10:13     ` Mickaël Salaün
2020-05-05 15:31 ` [PATCH v5 2/6] fs: Add a MAY_EXECMOUNT flag to infer the noexec mount property Mickaël Salaün
2020-05-12 21:09   ` Kees Cook
2020-05-14  8:14     ` Lev R. Oshvang .
2020-05-14 15:48       ` Kees Cook
2020-05-17 16:57         ` Lev R. Oshvang .
2020-05-05 15:31 ` [PATCH v5 3/6] fs: Enable to enforce noexec mounts or file exec through O_MAYEXEC Mickaël Salaün
2020-05-05 15:44   ` Randy Dunlap
2020-05-05 16:55     ` Mickaël Salaün
2020-05-05 17:40       ` Randy Dunlap
2020-05-12 21:48   ` Kees Cook
2020-05-13 11:09     ` Mickaël Salaün
2020-05-13 15:37   ` Stephen Smalley
2020-05-13 23:27     ` Kees Cook
2020-05-14  3:05       ` Kees Cook
2020-05-14 10:12         ` David Laight
2020-05-14 12:22         ` Stephen Smalley
2020-05-14 14:41           ` Kees Cook
2020-05-14 15:52             ` Stephen Smalley
2020-05-14 15:45           ` Kees Cook
2020-05-14 16:10             ` Stephen Smalley
2020-05-14 19:16               ` Mickaël Salaün
2020-05-15  0:58                 ` Tetsuo Handa
2020-05-15  8:01                 ` How about just O_EXEC? (was Re: [PATCH v5 3/6] fs: Enable to enforce noexec mounts or file exec through O_MAYEXEC) Kees Cook
2020-05-15  8:43                   ` Florian Weimer
2020-05-15 14:37                     ` Kees Cook
2020-05-15 14:43                       ` Florian Weimer
2020-05-15 15:50                         ` Kees Cook
2020-05-18  7:26                           ` Florian Weimer
2020-05-19  2:23                           ` Aleksa Sarai
2020-05-19 10:13                             ` Mickaël Salaün
2020-05-15 11:04                   ` Mickaël Salaün
2020-05-15 15:46                     ` Kees Cook
2020-05-15 18:24                       ` Mickaël Salaün
2020-05-14 19:21       ` Mickaël Salaün [this message]
2020-05-05 15:31 ` [PATCH v5 4/6] selftest/openat2: Add tests for O_MAYEXEC enforcing Mickaël Salaün
2020-05-12 21:57   ` Kees Cook
2020-05-13 11:18     ` Mickaël Salaün
2020-05-05 15:31 ` [PATCH v5 5/6] doc: Add documentation for the fs.open_mayexec_enforce sysctl Mickaël Salaün
2020-05-12 22:00   ` Kees Cook
2020-05-13 11:20     ` Mickaël Salaün
2020-05-05 15:31 ` [PATCH v5 6/6] ima: add policy support for the new file open MAY_OPENEXEC flag Mickaël Salaün
2020-05-05 15:36 ` [PATCH v5 0/6] Add support for O_MAYEXEC Mickaël Salaün
2020-05-06 13:58   ` Lev R. Oshvang .
2020-05-06 15:41     ` Aleksa Sarai
2020-05-07  8:30     ` Mickaël Salaün
2020-05-07  8:05 ` David Laight
2020-05-07  8:36   ` Mickaël Salaün
2020-05-07  9:00     ` David Laight
2020-05-07  9:30       ` Mickaël Salaün
2020-05-07  9:44         ` David Laight
2020-05-07 13:38           ` Mickaël Salaün
2020-05-08  7:15             ` Lev R. Oshvang .
2020-05-08 14:01               ` Mimi Zohar

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