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 <jeffv@google.com>
[PM: fixed return value of selinux_kernel_read_file()]
Signed-off-by: Paul Moore <paul@paul-moore.com>
diff --git a/security/selinux/include/classmap.h b/security/selinux/include/classmap.h
index ef83c4b..8fbd138 100644
--- a/security/selinux/include/classmap.h
+++ b/security/selinux/include/classmap.h
@@ -32,7 +32,7 @@
 	    "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",