xen: introduce xenbus_read_unsigned()

jira VULN-1439
cve-prereq CVE-2022-33741
commit-author Juergen Gross <[email protected]>
commit 9c53a17

There are multiple instances of code reading an optional unsigned
parameter from Xenstore via xenbus_scanf(). Instead of repeating the
same code over and over add a service function doing the job.

	Signed-off-by: Juergen Gross <[email protected]>
	Reviewed-by: David Vrabel <[email protected]>
(cherry picked from commit 9c53a17)
	Signed-off-by: Brett Mastbergen <[email protected]>

Author: bmastbergen

drivers/xen/xenbus/xenbus_xs.c

@@ -526,6 +526,21 @@ int xenbus_scanf(struct xenbus_transaction t,
 }
 EXPORT_SYMBOL_GPL(xenbus_scanf);
 
+/* Read an (optional) unsigned value. */
+unsigned int xenbus_read_unsigned(const char *dir, const char *node,
+				  unsigned int default_val)
+{
+	unsigned int val;
+	int ret;
+
+	ret = xenbus_scanf(XBT_NIL, dir, node, "%u", &val);
+	if (ret <= 0)
+		val = default_val;
+
+	return val;
+}
+EXPORT_SYMBOL_GPL(xenbus_read_unsigned);
+
 /* Single printf and write: returns -errno or 0. */
 int xenbus_printf(struct xenbus_transaction t,
 		  const char *dir, const char *node, const char *fmt, ...)

include/xen/xenbus.h

@@ -144,6 +144,10 @@ __scanf(4, 5)
 int xenbus_scanf(struct xenbus_transaction t,
 		 const char *dir, const char *node, const char *fmt, ...);
 
+/* Read an (optional) unsigned value. */
+unsigned int xenbus_read_unsigned(const char *dir, const char *node,
+				  unsigned int default_val);
+
 /* Single printf and write: returns -errno or 0. */
 __printf(4, 5)
 int xenbus_printf(struct xenbus_transaction t,