libio: Flush stream at freopen (BZ#21037)

As POSIX states [1] a freopen call should first flush the stream as if by a
call fflush.  C99 (n1256) and C11 (n1570) only states the function should
first close any file associated with the specific stream.  Although current
implementation only follow C specification, current BSD and other libc
implementation (musl) are in sync with POSIX and fflush the stream.

This patch change freopen{64} to fflush the stream before actually reopening
it (or returning if the stream does not support reopen).  It also changes the
Linux implementation to avoid a dynamic allocation on 'fd_to_filename'.

Checked on x86_64-linux-gnu.

	[BZ #21037]
	* libio/Makefile (tests): Add tst-memstream4 and tst-wmemstream4.
	* libio/freopen.c (freopen): Sync stream before reopen and adjust to
	new fd_to_filename interface.
	* libio/freopen64.c (freopen64): Likewise.
	* libio/tst-memstream.h: New file.
	* libio/tst-memstream4.c: Likewise.
	* libio/tst-wmemstream4.c: Likewise.
	* sysdeps/generic/fd_to_filename.h (fd_to_filename): Change signature.
	* sysdeps/unix/sysv/linux/fd_to_filename.h (fd_to_filename): Likewise
	and remove internal dynamic allocation.

[1] http://pubs.opengroup.org/onlinepubs/9699919799/

1 files changed, 16 insertions, 13 deletions

diff --git a/libio/freopen.c b/libio/freopen.c
index abf19e96f1..6ce74ae449 100644
--- a/libio/freopen.c
+++ b/libio/freopen.c
@@ -24,28 +24,34 @@
    This exception applies to code released by its copyright holders
    in files containing the exception.  */
 
-#include "libioP.h"
-#include "stdio.h"
+#include <stdio.h>
 #include <fcntl.h>
 #include <stdlib.h>
 #include <unistd.h>
 
-#include <shlib-compat.h>
+#include <libioP.h>
 #include <fd_to_filename.h>
-
-#include <kernel-features.h>
+#include <shlib-compat.h>
 
 FILE *
 freopen (const char *filename, const char *mode, FILE *fp)
 {
-  FILE *result;
+  FILE *result = NULL;
+  char fdfilename[FD_TO_FILENAME_SIZE];
+
   CHECK_FILE (fp, NULL);
-  if (!(fp->_flags & _IO_IS_FILEBUF))
-    return NULL;
+
   _IO_acquire_lock (fp);
+  /* First flush the stream (failure should be ignored).  */
+  _IO_SYNC (fp);
+
+  if (!(fp->_flags & _IO_IS_FILEBUF))
+    goto end;
+
   int fd = _IO_fileno (fp);
-  const char *gfilename = (filename == NULL && fd >= 0
-			   ? fd_to_filename (fd) : filename);
+  const char *gfilename
+    = filename != NULL ? filename : fd_to_filename (fd, fdfilename);
+
   fp->_flags2 |= _IO_FLAGS2_NOCLOSE;
 #if SHLIB_COMPAT (libc, GLIBC_2_0, GLIBC_2_1)
   if (&_IO_stdin_used == NULL)
@@ -101,9 +107,6 @@ freopen (const char *filename, const char *mode, FILE *fp)
     __close (fd);
 
 end:
-  if (filename == NULL)
-    free ((char *) gfilename);
-
   _IO_release_lock (fp);
   return result;
 }