selinux: restrict kernel module loading

Utilize existing kernel_read_file hook on kernel module load.
Add module_load permission to the system class.

Enforces restrictions on kernel module origin when calling the
finit_module syscall. The hook checks that source type has
permission module_load for the target type.
Example for finit_module:

allow foo bar_file:system module_load;

Similarly restrictions are enforced on kernel module loading when
calling the init_module syscall. The hook checks that source
type has permission module_load with itself as the target object
because the kernel module is sourced from the calling process.
Example for init_module:

allow foo foo:system module_load;

Signed-off-by: Jeff Vander Stoep <[e-mail]>
[PM: fixed return value of selinux_kernel_read_file()]
Signed-off-by: Paul Moore <[e-mail]>

security/selinux/hooks.c

···
 			    SYSTEM__MODULE_REQUEST, &ad);
 }
 
+static int selinux_kernel_module_from_file(struct file *file)
+{
+	struct common_audit_data ad;
+	struct inode_security_struct *isec;
+	struct file_security_struct *fsec;
+	u32 sid = current_sid();
+	int rc;
+
+	/* init_module */
+	if (file == NULL)
+		return avc_has_perm(sid, sid, SECCLASS_SYSTEM,
+					SYSTEM__MODULE_LOAD, NULL);
+
+	/* finit_module */
+	ad.type = LSM_AUDIT_DATA_PATH;
+	ad.u.path = file->f_path;
+
+	isec = inode_security(file_inode(file));
+	fsec = file->f_security;
+
+	if (sid != fsec->sid) {
+		rc = avc_has_perm(sid, fsec->sid, SECCLASS_FD, FD__USE, &ad);
+		if (rc)
+			return rc;
+	}
+
+	return avc_has_perm(sid, isec->sid, SECCLASS_SYSTEM,
+				SYSTEM__MODULE_LOAD, &ad);
+}
+
+static int selinux_kernel_read_file(struct file *file,
+				    enum kernel_read_file_id id)
+{
+	int rc = 0;
+
+	switch (id) {
+	case READING_MODULE:
+		rc = selinux_kernel_module_from_file(file);
+		break;
+	default:
+		break;
+	}
+
+	return rc;
+}
+
 static int selinux_task_setpgid(struct task_struct *p, pid_t pgid)
 {
 	return current_has_perm(p, PROCESS__SETPGID);
···
 	LSM_HOOK_INIT(kernel_act_as, selinux_kernel_act_as),
 	LSM_HOOK_INIT(kernel_create_files_as, selinux_kernel_create_files_as),
 	LSM_HOOK_INIT(kernel_module_request, selinux_kernel_module_request),
+	LSM_HOOK_INIT(kernel_read_file, selinux_kernel_read_file),
 	LSM_HOOK_INIT(task_setpgid, selinux_task_setpgid),
 	LSM_HOOK_INIT(task_getpgid, selinux_task_getpgid),
 	LSM_HOOK_INIT(task_getsid, selinux_task_getsid),

security/selinux/include/classmap.h

···
 	    "setsockcreate", NULL } },
 	{ "system",
 	  { "ipc_info", "syslog_read", "syslog_mod",
-	    "syslog_console", "module_request", NULL } },
+	    "syslog_console", "module_request", "module_load", NULL } },
 	{ "capability",
 	  { "chown", "dac_override", "dac_read_search",
 	    "fowner", "fsetid", "kill", "setgid", "setuid", "setpcap",