lib/string.c: allow searching for NUL with strnchr

Patch series "lib/string: search for NUL with strchr/strnchr". I noticed an inconsistency where strchr and strnchr do not behave the same with respect to the trailing NUL. strchr is standardised and the kernel function conforms, and the kernel relies on the behavior. So, naturally strchr stays as-is and strnchr is what I change. While writing a few tests to verify that my new strnchr loop was sane, I noticed that the tests for memset16/32/64 had a problem. Since it's all about the lib/string.c file I made a short series of it all... This patch (of 3): strchr considers the terminating NUL to be part of the string, and NUL can thus be searched for with that function. For consistency, do the same with strnchr. Link: http://lkml.kernel.org/r/[email protected] Signed-off-by: Peter Rosin <[email protected]> Cc: Matthew Wilcox <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]>
mrcsosa · Jul 17, 2019 · b097571 · b097571
1 parent 4c6080c
commit b097571
Showing 1 changed file with 10 additions and 1 deletion.
diff --git a/lib/string.c b/lib/string.c
@@ -400,6 +400,9 @@ EXPORT_SYMBOL(strncmp);
  * strchr - Find the first occurrence of a character in a string
  * @s: The string to be searched
  * @c: The character to search for
+ *
+ * Note that the %NUL-terminator is considered part of the string, and can
+ * be searched for.
  */
 char *strchr(const char *s, int c)
 {
@@ -453,12 +456,18 @@ EXPORT_SYMBOL(strrchr);
  * @s: The string to be searched
  * @count: The number of characters to be searched
  * @c: The character to search for
+ *
+ * Note that the %NUL-terminator is considered part of the string, and can
+ * be searched for.
  */
 char *strnchr(const char *s, size_t count, int c)
 {
-	for (; count-- && *s != '\0'; ++s)
+	while (count--) {
 		if (*s == (char)c)
 			return (char *)s;
+		if (*s++ == '\0')
+			break;
+	}
 	return NULL;
 }
 EXPORT_SYMBOL(strnchr);