Re: [PATCH v30 08/12] landlock: Add syscall implementations

From: "Mickaël Salaün" <mic@digikod.net>
To: Kees Cook <keescook@chromium.org>
Cc: "James Morris" <jmorris@namei.org>,
	"Jann Horn" <jannh@google.com>,
	"Serge E . Hallyn" <serge@hallyn.com>,
	"Al Viro" <viro@zeniv.linux.org.uk>,
	"Andrew Morton" <akpm@linux-foundation.org>,
	"Andy Lutomirski" <luto@amacapital.net>,
	"Anton Ivanov" <anton.ivanov@cambridgegreys.com>,
	"Arnd Bergmann" <arnd@arndb.de>,
	"Casey Schaufler" <casey@schaufler-ca.com>,
	"David Howells" <dhowells@redhat.com>,
	"Jeff Dike" <jdike@addtoit.com>,
	"Jonathan Corbet" <corbet@lwn.net>,
	"Michael Kerrisk" <mtk.manpages@gmail.com>,
	"Richard Weinberger" <richard@nod.at>,
	"Shuah Khan" <shuah@kernel.org>,
	"Vincent Dagonneau" <vincent.dagonneau@ssi.gouv.fr>,
	kernel-hardening@lists.openwall.com, linux-api@vger.kernel.org,
	linux-arch@vger.kernel.org, linux-doc@vger.kernel.org,
	linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-kselftest@vger.kernel.org,
	linux-security-module@vger.kernel.org, x86@kernel.org,
	"Mickaël Salaün" <mic@linux.microsoft.com>
Subject: Re: [PATCH v30 08/12] landlock: Add syscall implementations
Date: Wed, 24 Mar 2021 16:03:36 +0100	[thread overview]
Message-ID: <9062d586-8fa7-a972-9615-ca3a5fe38cef@digikod.net> (raw)
In-Reply-To: <380d65b2-f515-f3f5-5d57-7f99c528e5c7@digikod.net>

On 19/03/2021 22:53, Mickaël Salaün wrote:
> 
> On 19/03/2021 20:06, Kees Cook wrote:
>> On Tue, Mar 16, 2021 at 09:42:48PM +0100, Mickaël Salaün wrote:
>>> From: Mickaël Salaün <mic@linux.microsoft.com>

[...]

>>> +/**
>>> + * sys_landlock_create_ruleset - Create a new ruleset
>>> + *
>>> + * @attr: Pointer to a &struct landlock_ruleset_attr identifying the scope of
>>> + *        the new ruleset.
>>> + * @size: Size of the pointed &struct landlock_ruleset_attr (needed for
>>> + *        backward and forward compatibility).
>>> + * @flags: Must be 0.
>>> + *
>>> + * This system call enables to create a new Landlock ruleset, and returns the
>>> + * related file descriptor on success.
>>> + *
>>> + * Possible returned errors are:
>>> + *
>>> + * - EOPNOTSUPP: Landlock is supported by the kernel but disabled at boot time;
>>> + * - EINVAL: @flags is not 0, or unknown access, or too small @size;
>>> + * - E2BIG or EFAULT: @attr or @size inconsistencies;
>>> + * - ENOMSG: empty &landlock_ruleset_attr.handled_access_fs.
>>> + */
>>> +SYSCALL_DEFINE3(landlock_create_ruleset,
>>> +		const struct landlock_ruleset_attr __user *const, attr,
>>> +		const size_t, size, const __u32, flags)
>>> +{
>>> +	struct landlock_ruleset_attr ruleset_attr;
>>> +	struct landlock_ruleset *ruleset;
>>> +	int err, ruleset_fd;
>>> +
>>> +	/* Build-time checks. */
>>> +	build_check_abi();
>>> +
>>> +	if (!landlock_initialized)
>>> +		return -EOPNOTSUPP;
>>> +
>>> +	/* No flag for now. */
>>> +	if (flags)
>>> +		return -EINVAL;
>>> +
>>> +	/* Copies raw user space buffer. */
>>> +	err = copy_min_struct_from_user(&ruleset_attr, sizeof(ruleset_attr),
>>> +			offsetofend(typeof(ruleset_attr), handled_access_fs),
>>
>> The use of offsetofend() here appears to be kind of the "V1", "V2", ...
>> sizes used in other extensible syscall implementations?
> 
> ruleset_attr is an extensible argument.

offsetofen() is used to set the minimum size of a valid argument. This
code will then not change with future extended ruleset_attr.