libio: Fix fmemopen 'w' mode with provided buffer

If 'w' mode is used with a provided buffer the fmemopen will try to find
the first null byte to set as maximum internal stream size.  It should be
done only for append mode ('a').

Kudos for Stefan Liebler for finding this error on s390-32.

	* libio/fmemopen.c (__fmemopen): Fix 'w' openmode with provided
	buffer.
	* stdio-common/tst-fmemopen2.c (do_test_with_buffer): Fix typo and
	fail output information.

ChangeLog

@@ -1,3 +1,10 @@
+2015-07-16  Adhemerval Zanella  <adhemerval.zanella@linaro.org>
+
+	* libio/fmemopen.c (__fmemopen): Fix 'w' openmode with provided
+	buffer.
+	* stdio-common/tst-fmemopen2.c (do_test_with_buffer): Fix typo and
+	fail output information.
+
 2015-07-16  Rajalakshmi Srinivasaraghavan  <raji@linux.vnet.ibm.com>
 
 	* sysdeps/powerpc/powerpc64/multiarch/Makefile: Add strstr-power7

libio/fmemopen.c

@@ -150,7 +150,7 @@ __fmemopen (void *buf, size_t len, const char *mode)
   cookie_io_functions_t iof;
   fmemopen_cookie_t *c;
 
-  c = (fmemopen_cookie_t *) malloc (sizeof (fmemopen_cookie_t));
+  c = (fmemopen_cookie_t *) calloc (sizeof (fmemopen_cookie_t), 1);
   if (c == NULL)
     return NULL;
 
@@ -165,7 +165,6 @@ __fmemopen (void *buf, size_t len, const char *mode)
 	  return NULL;
 	}
       c->buffer[0] = '\0';
-      c->maxpos = 0;
     }
   else
     {
@@ -182,7 +181,8 @@ __fmemopen (void *buf, size_t len, const char *mode)
       if (mode[0] == 'w' && mode[1] == '+')
 	c->buffer[0] = '\0';
 
-      c->maxpos = strnlen (c->buffer, len);
+      if (mode[0] == 'a')
+        c->maxpos = strnlen (c->buffer, len);
     }
 
 

stdio-common/tst-fmemopen2.c

@@ -34,7 +34,7 @@ do_test_with_buffer (void)
   FILE *fp = fmemopen (buf, nbuf, "w");
   if (fp == NULL)
     {
-      printf ("FAIL: fmemopen failedi (%s)\n", __FUNCTION__);
+      printf ("FAIL: fmemopen failed (%s)\n", __FUNCTION__);
       return 1;
     }
 
@@ -69,7 +69,7 @@ do_test_with_buffer (void)
   if (o != nstr)
     {
       printf ("FAIL: third ftello returned %jd, expected %zu\n",
-	      (intmax_t)o, nbuf);
+	      (intmax_t)o, nstr);
       result = 1;
     }