vsprintf: add simple_strntoul

cpio extraction currently does a memcpy to ensure that the archive hex
fields are null terminated for simple_strtoul(). simple_strntoul() will
allow us to avoid the memcpy.

Signed-off-by: David Disseldorp <ddiss@suse.de>
Link: https://lore.kernel.org/r/20250304061020.9815-4-ddiss@suse.de
Signed-off-by: Christian Brauner <brauner@kernel.org>

Author: ddiss

include/linux/kstrtox.h

@@ -143,6 +143,7 @@ static inline int __must_check kstrtos32_from_user(const char __user *s, size_t
  */
 
 extern unsigned long simple_strtoul(const char *,char **,unsigned int);
+extern unsigned long simple_strntoul(const char *,char **,unsigned int,size_t);
 extern long simple_strtol(const char *,char **,unsigned int);
 extern unsigned long long simple_strtoull(const char *,char **,unsigned int);
 extern long long simple_strtoll(const char *,char **,unsigned int);

lib/vsprintf.c

@@ -114,6 +114,13 @@ unsigned long simple_strtoul(const char *cp, char **endp, unsigned int base)
 }
 EXPORT_SYMBOL(simple_strtoul);
 
+unsigned long simple_strntoul(const char *cp, char **endp, unsigned int base,
+			      size_t max_chars)
+{
+	return simple_strntoull(cp, endp, base, max_chars);
+}
+EXPORT_SYMBOL(simple_strntoul);
+
 /**
  * simple_strtol - convert a string to a signed long
  * @cp: The start of the string