BACKPORT: selinux: restrict kernel module loading

Backport notes:
Backport uses kernel_module_from_file not kernel_read_file hook.
kernel_read_file replaced kernel_module_from_file in the 4.6 kernel.
There are no inode_security_() helper functions (also introduced in
4.6) so the inode lookup is done using the file_inode() helper which
is standard for kernel version < 4.6.

(Cherry picked from commit 61d612e)

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;

Bug: 27824855
Change-Id: I64bf3bd1ab2dc735321160642dc6bbfa996f8068
Signed-off-by: Jeff Vander Stoep <jeffv@google.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>

security/selinux/hooks.c

@@ -3660,6 +3660,38 @@ static int selinux_kernel_module_request(char *kmod_name)
 			    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;
+	struct inode *inode;
+	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;
+
+	inode = file_inode(file);
+	isec = inode->i_security;
+	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_task_setpgid(struct task_struct *p, pid_t pgid)
 {
 	return current_has_perm(p, PROCESS__SETPGID);
@@ -5950,6 +5982,7 @@ static struct security_hook_list selinux_hooks[] = {
 	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_module_from_file, selinux_kernel_module_from_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

@@ -32,7 +32,7 @@ struct security_class_mapping secclass_map[] = {
 	    "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",