On 19/03/2021 22:53, Mickaël Salaün wrote:

On 19/03/2021 20:06, Kees Cook wrote:

quoted

On Tue, Mar 16, 2021 at 09:42:48PM +0100, Mickaël Salaün wrote:

quoted

From: Mickaël Salaün <redacted>

[...]

quoted

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+/**
+ * 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.