s390: fix strrchr() implementation

commit 8e0ab8e26b72a80e991c66a8abc16e6c856abe3d upstream.

Fix two problems found in the strrchr() implementation for s390
architectures: evaluate empty strings (return the string address instead of
NULL, if '\0' is passed as second argument); evaluate the first character
of non-empty strings (the current implementation stops at the second).

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Cc: stable@vger.kernel.org
Reported-by: Heiko Carstens <hca@linux.ibm.com> (incorrect behavior with empty strings)
Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
Link: https://lore.kernel.org/r/20211005120836.60630-1-roberto.sassu@huawei.com
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/s390/lib/string.c b/arch/s390/lib/string.c
index 0e30e6e43b0c51dfd1a1adf1fc7a6d45bd022dd1..18fbbb679851df8406f0059804f888042d001ef2 100644 (file)
--- a/arch/s390/lib/string.c
+++ b/arch/s390/lib/string.c
@@ -246,14 +246,13 @@ EXPORT_SYMBOL(strcmp);
 #ifdef __HAVE_ARCH_STRRCHR
 char *strrchr(const char *s, int c)
 {
-       size_t len = __strend(s) - s;
-
-       if (len)
-              do {
-                      if (s[len] == (char) c)
-                              return (char *) s + len;
-              } while (--len > 0);
-       return NULL;
+       ssize_t len = __strend(s) - s;
+
+       do {
+               if (s[len] == (char)c)
+                       return (char *)s + len;
+       } while (--len >= 0);
+       return NULL;
 }
 EXPORT_SYMBOL(strrchr);
 #endif