vfs: define kernel_read_file_id enumeration

To differentiate between the kernel_read_file() callers, this patch
defines a new enumeration named kernel_read_file_id and includes the
caller identifier as an argument.

Subsequent patches define READING_KEXEC_IMAGE, READING_KEXEC_INITRAMFS,
READING_FIRMWARE, READING_MODULE, and READING_POLICY.

Changelog v3:
- Replace the IMA specific enumeration with a generic one.

Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com>
Acked-by: Kees Cook <keescook@chromium.org>
Acked-by: Luis R. Rodriguez <mcgrof@kernel.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>

security/security.c

@@ -910,9 +910,10 @@ int security_kernel_module_from_file(struct file *file)
 	return ima_module_check(file);
 }
 
-int security_kernel_post_read_file(struct file *file, char *buf, loff_t size)
+int security_kernel_post_read_file(struct file *file, char *buf, loff_t size,
+				   enum kernel_read_file_id id)
 {
-	return call_int_hook(kernel_post_read_file, 0, file, buf, size);
+	return call_int_hook(kernel_post_read_file, 0, file, buf, size, id);
 }
 EXPORT_SYMBOL_GPL(security_kernel_post_read_file);