security: introduce kernel_fw_from_file hook

In order to validate the contents of firmware being loaded, there must be
a hook to evaluate any loaded firmware that wasn't built into the kernel
itself. Without this, there is a risk that a root user could load malicious
firmware designed to mount an attack against kernel memory (e.g. via DMA).

Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Takashi Iwai <tiwai@suse.de>

security/capability.c

@@ -401,6 +401,11 @@ static int cap_kernel_create_files_as(struct cred *new, struct inode *inode)
 	return 0;
 }
 
+static int cap_kernel_fw_from_file(struct file *file, char *buf, size_t size)
+{
+	return 0;
+}
+
 static int cap_kernel_module_request(char *kmod_name)
 {
 	return 0;
@@ -1015,6 +1020,7 @@ void __init security_fixup_ops(struct security_operations *ops)
 	set_to_cap_if_null(ops, cred_transfer);
 	set_to_cap_if_null(ops, kernel_act_as);
 	set_to_cap_if_null(ops, kernel_create_files_as);
+	set_to_cap_if_null(ops, kernel_fw_from_file);
 	set_to_cap_if_null(ops, kernel_module_request);
 	set_to_cap_if_null(ops, kernel_module_from_file);
 	set_to_cap_if_null(ops, task_fix_setuid);

security/security.c

@@ -845,6 +845,12 @@ int security_kernel_create_files_as(struct cred *new, struct inode *inode)
 	return security_ops->kernel_create_files_as(new, inode);
 }
 
+int security_kernel_fw_from_file(struct file *file, char *buf, size_t size)
+{
+	return security_ops->kernel_fw_from_file(file, buf, size);
+}
+EXPORT_SYMBOL_GPL(security_kernel_fw_from_file);
+
 int security_kernel_module_request(char *kmod_name)
 {
 	return security_ops->kernel_module_request(kmod_name);