use strnlen() in vfprintf.c

[Todd C. Miller]

This is what strnlen(3) is for, let's use it...

Alternately, we could unify things like:

        len = prec >= 0 ? strnlen(cp, prec) : strlen(cp);
        if (len > INT_MAX)
                goto overflow;
        size = (int)len;

but that means declaring "size_t len" at the top of the for(;;) loop.

 - todd

Index: lib/libc/stdio/vfprintf.c
===================================================================
RCS file: /cvs/src/lib/libc/stdio/vfprintf.c,v
retrieving revision 1.75
diff -u -p -u -r1.75 vfprintf.c
--- lib/libc/stdio/vfprintf.c   17 Aug 2016 22:15:08 -0000      1.75
+++ lib/libc/stdio/vfprintf.c   25 Aug 2016 18:12:42 -0000
@@ -887,14 +887,11 @@ fp_common:
                                cp = "(null)";
                        }
                        if (prec >= 0) {
-                               /*
-                                * can't use strlen; can only look for the
-                                * NUL in the first `prec' characters, and
-                                * strlen() will go further.
-                                */
-                               char *p = memchr(cp, 0, prec);
+                               size_t len;
 
-                               size = p ? (p - cp) : prec;
+                               if ((len = strnlen(cp, prec)) > INT_MAX)
+                                       goto overflow;
+                               size = (int)len;
                        } else {
                                size_t len;