libio: Update internal fmemopen position after write (BZ #20005)

Current GLIBC fmemopen fails with a simple testcase:

  char buffer[500] = "x";
  FILE *stream;
  stream = fmemopen(buffer, 500, "r+");
  fwrite("fish",sizeof(char),5,stream);
  printf("pos-1:%ld\n",ftell(stream));
  fflush(stream);
  printf("pos-2:%ld\n",ftell(stream));

It returns:

  pos-1:5
  pos-2:0

Where it should return:

  pos-1:5
  pos-2:5

This is due the internal write function does not correctly update the internal
object position state and then the seek operation returns a wrong value.  This
patch fixes it.

It fixes both BZ #20005 and BZ #19230 (marked as duplicated). A new test is
added to check for such case.

Tested on x86_64 and i686.

This is a backport of f9123b5003e62b6e54996076e860f23aee9a0593.

	* libio/fmemopen.c (fmemopen_write): Update internal position after
	write.
	* stdio-common/Makefile (tests): Add tst-fmemopen4.c.
	* stdio-common/tst-fmemopen4.c: New file..

(cherry picked from commit c2fba3b047c2fac50985a47ff96075b5d9078432)

3 files changed, 75 insertions, 4 deletions

diff --git a/libio/fmemopen.c b/libio/fmemopen.c
index 23b5c5fea8..9264b724ee 100644
--- a/libio/fmemopen.c
+++ b/libio/fmemopen.c
@@ -86,10 +86,10 @@ fmemopen_write (void *cookie, const char *b, size_t s)
 
   memcpy (&(c->buffer[pos]), b, s);
 
-  pos += s;
-  if ((size_t) pos > c->maxpos)
+  c->pos += s;
+  if ((size_t) c->pos > c->maxpos)
     {
-      c->maxpos = pos;
+      c->maxpos = c->pos;
       if (addnullc)
 	c->buffer[c->maxpos] = '\0';
     }
diff --git a/stdio-common/Makefile b/stdio-common/Makefile
index cc79d347bc..83ff00a482 100644
--- a/stdio-common/Makefile
+++ b/stdio-common/Makefile
@@ -58,7 +58,7 @@ tests := tstscanf test_rdwr test-popen tstgetln test-fseek \
 	 scanf16 scanf17 tst-setvbuf1 tst-grouping bug23 bug24 \
 	 bug-vfprintf-nargs tst-long-dbl-fphex tst-fphex-wide tst-sprintf3 \
 	 bug25 tst-printf-round bug23-2 bug23-3 bug23-4 bug26 tst-fmemopen3 \
-	 tst-printf-bz18872
+	 tst-printf-bz18872 tst-fmemopen4
 
 test-srcs = tst-unbputc tst-printf
 
diff --git a/stdio-common/tst-fmemopen4.c b/stdio-common/tst-fmemopen4.c
new file mode 100644
index 0000000000..e24f1cacd9
--- /dev/null
+++ b/stdio-common/tst-fmemopen4.c
@@ -0,0 +1,71 @@
+/* fmemopen tests for BZ#1930 and BZ#20005.
+   Copyright (C) 2016 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include <assert.h>
+#include <stdio.h>
+#include <string.h>
+#include <sys/types.h>
+
+
+/* Check if fflush does not reset the file position.  */
+static int
+do_test (void)
+{
+  char buffer[500] = "x";
+
+  FILE *stream = fmemopen (buffer, sizeof (buffer), "r+");
+  if (stream == NULL)
+    {
+      printf ("error: fmemopen could not open stream\n");
+      return 1;
+    }
+
+  const char test[] = "test";
+
+  size_t r = fwrite (test, sizeof (char), sizeof (test), stream);
+  if (r != sizeof (test))
+    {
+      printf ("error: fwrite returned %zu, expected %zu\n", r, sizeof(test));
+      return 1;
+    }
+
+  r = ftell (stream);
+  if (r != sizeof (test))
+    {
+      printf ("error: ftell return %zu, expected %zu\n", r, sizeof(test));
+      return 1;
+    }
+
+  if (fflush (stream) != 0)
+    {
+      printf ("error: fflush failed\n");
+      return 1;
+    }
+
+  r = ftell (stream);
+  if (r != sizeof (test))
+    {
+      printf ("error: ftell return %zu, expected %zu\n", r, sizeof(test));
+      return 1;
+    }
+
+  return 0;
+}
+
+#define TEST_FUNCTION do_test ()
+#include "../test-skeleton.c"