return false instead of empty string when -length is greater than (len - offset)

diff --git a/ext/standard/string.c b/ext/standard/string.c
index 7e32ba33f53059d5f6eb28b0d9d003d8ce76ccad..86738ff4ac61f62983441c443615e1330fb4eead 100644 (file)
--- a/ext/standard/string.c
+++ b/ext/standard/string.c
@@ -2077,6 +2077,10 @@ PHP_FUNCTION(substr)
                RETURN_FALSE;
        }
 
+       if (l < 0 && (l + Z_STRLEN_PP(str) - f) < 0) {
+               RETURN_FALSE;
+       }
+
        /* if "from" position is negative, count start position from the end
         * of the string
         */