Re: [PATCH][BZ #16398] Fix infinite loop in ftell when writing wide char data

[Siddhesh Poyarekar <siddhesh at redhat dot com>]

On Fri, Jan 31, 2014 at 11:26:06AM -0800, Roland McGrath wrote:
> Most test cases are pretty small such that either copyright doesn't apply
> (if really tiny) or it's simple enough to rewrite the case from scratch
> once you roughly grok the bug.  

OK, I just rewrote the test case.  Tested on x86_64 and ppc64.  OK to
commit?

Siddhesh

	[BZ #16398]
	* libio/wfileops.c (_IO_wfile_seekoff): Break out form
	conversion when destination buffer does not have enough space.
	* libio/tst-ftell-partial-wide.c: New test case.
	* libio/Makefile (tests): Add tst-ftell-partial-wide.


commit 6be430aa57633d9a4c383e0bb72806eb81243d79
Author: Siddhesh Poyarekar <siddhesh@redhat.com>
Date:   Mon Feb 3 15:20:44 2014 +0530

    Fix infinite loop in ftell when writing wide char data (BZ #16398)
    
    ftell tries to avoid flushing the buffer when it is in write mode by
    converting the wide char data and placing it into the binary buffer.
    If the output buffer space is full and there is data to write, the
    code reverts to flushing the buffer.  This breaks when there is space
    in the buffer but it is not enough to convert the next character in
    the wide data buffer, due to which __codecvt_do_out returns a
    __codecvt_partial status.  In this case, ftell keeps running in an
    infinite loop.
    
    The fix here is to detect the __codecvt_partial status in addition to
    checking if the buffer is full.  I have also added a test case
    (written by Arjun Shankar) that demonstrates the infinite loop.

diff --git a/libio/Makefile b/libio/Makefile
index 05432f4..747a779 100644
--- a/libio/Makefile
+++ b/libio/Makefile
@@ -60,7 +60,7 @@ tests = tst_swprintf tst_wprintf tst_swscanf tst_wscanf tst_getwc tst_putwc   \
 	tst-wmemstream1 tst-wmemstream2 \
 	bug-memstream1 bug-wmemstream1 \
 	tst-setvbuf1 tst-popen1 tst-fgetwc bug-wsetpos tst-fseek \
-	tst-fwrite-error
+	tst-fwrite-error tst-ftell-partial-wide
 ifeq (yes,$(build-shared))
 # Add test-fopenloc only if shared library is enabled since it depends on
 # shared localedata objects.
diff --git a/libio/tst-ftell-partial-wide.c b/libio/tst-ftell-partial-wide.c
new file mode 100644
index 0000000..0c4dede
--- /dev/null
+++ b/libio/tst-ftell-partial-wide.c
@@ -0,0 +1,104 @@
+/* Verify that ftell does not go into an infinite loop when a conversion fails
+   due to insufficient space in the buffer.
+   Copyright (C) 2014 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 <wchar.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <locale.h>
+#include <errno.h>
+#include <unistd.h>
+
+/* Defined in test-skeleton.c.  */
+static int create_temp_file (const char *base, char **filename);
+
+/* Large enough that the target buffer during conversion is not large
+   enough.  I found this by just tinkering with the numbers till I found a
+   small enough number.  */
+#define STRING_SIZE (1400)
+#define NSTRINGS (2)
+
+int
+do_test (void)
+{
+  FILE *fp = NULL;
+  wchar_t *inputs[NSTRINGS] = {NULL};
+  int ret = 1;
+
+  if (setlocale (LC_ALL, "en_US.UTF-8") == NULL)
+    {
+      printf ("Cannot set en_US.UTF-8 locale.\n");
+      goto out;
+    }
+
+
+  /* Generate input from one character.  */
+  wchar_t seed = L'ã';
+  for (int i = 0; i < NSTRINGS; i++)
+    {
+      inputs[i] = malloc (STRING_SIZE * sizeof (wchar_t));
+      if (inputs[i] == NULL)
+	{
+	  printf ("Failed to allocate memory for inputs: %m\n");
+	  goto out;
+	}
+      wmemset (inputs[i], seed, STRING_SIZE - 1);
+      inputs[i][STRING_SIZE - 1] = L'\0';
+    }
+
+  char *filename;
+  int fd = create_temp_file ("tst-fseek-wide-partial.out", &filename);
+
+  if (fd == -1)
+    {
+      printf ("create_temp_file: %m\n");
+      goto out;
+    }
+
+  fp = fdopen (fd, "w+");
+  if (fp == NULL)
+    {
+      printf ("fopen: %m\n");
+      close (fd);
+      goto out;
+    }
+
+  for (int i = 0; i < NSTRINGS; i++)
+    {
+      printf ("offset: %ld\n", ftell (fp));
+      if (fputws (inputs[i], fp) == -1)
+        {
+          perror ("fputws");
+	  goto out;
+        }
+    }
+  ret = 0;
+
+out:
+  if (fp != NULL)
+    fclose (fp);
+  for (int i = 0; i < NSTRINGS; i++)
+    free (inputs[i]);
+
+  return ret;
+}
+
+
+#define TEST_FUNCTION do_test ()
+#include "../test-skeleton.c"
diff --git a/libio/wfileops.c b/libio/wfileops.c
index 87d3cdc..877fc1f 100644
--- a/libio/wfileops.c
+++ b/libio/wfileops.c
@@ -715,7 +715,7 @@ _IO_wfile_seekoff (fp, offset, dir, mode)
 		       - fp->_wide_data->_IO_write_base) / clen;
 	  else
 	    {
-	      enum __codecvt_result status;
+	      enum __codecvt_result status = __codecvt_ok;
 	      delta = (fp->_wide_data->_IO_write_ptr
 		       - fp->_wide_data->_IO_write_base);
 	      const wchar_t *write_base = fp->_wide_data->_IO_write_base;
@@ -728,9 +728,12 @@ _IO_wfile_seekoff (fp, offset, dir, mode)
 		 flush buffers for every ftell.  */
 	      do
 		{
-		  /* Ugh, no point trying to avoid the flush.  Just do it
-		     and go back to how it was with the read mode.  */
-		  if (delta > 0 && new_write_ptr == fp->_IO_buf_end)
+		  /* There is not enough space in the buffer to do the entire
+		     conversion, so there is no point trying to avoid the
+		     buffer flush.  Just do it and go back to how it was with
+		     the read mode.  */
+		  if (status == __codecvt_partial
+		      || (delta > 0 && new_write_ptr == fp->_IO_buf_end))
 		    {
 		      if (_IO_switch_to_wget_mode (fp))
 			return WEOF;