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f1a67a2c78
As described in BZ#21398 (close as dup of 21393) report current freopen implementation fails when one tries to freopen STDIN_FILENO, STDOUT_FILENO, or STDERR_FILENO. Although on bug report the discussion leads to argue if a close followed by a freopen on the standard file is a valid operation, the underlying issue is not really the check for dup3 returned value, but rather calling it if the returned file descriptor is equal as the input one. So for a quality of implementation this patch avoid calling dup3 for the aforementioned case. It also adds a dup3 error case check for the two possible failures, with one being Linux only: EINTR and EBUSY. The EBUSY issue is better explained on this stackoverflow thread [1], but in a short it is due the internal Linux implementation which allows a race condition window for dup2 due the logic dissociation of file descriptor allocation and actual VFS 'install' operation. For both outliers failures all allocated memory is freed and a NULL FILE* is returned. With this patch the example on BZ#21398 is now actually possible (I used as the testcase for the bug report). Checked on x86_64-linux-gnu. [BZ #21393] * libio/freopen.c (freopen): Avoid dup already opened file descriptor and add a check for dup3 failure. * libio/freopen64.c (freopen64): Likewise. * libio/tst-freopen.c (do_test): Rename to do_test_basic and use libsupport. (do_test_bz21398): New test. * manual/stdio.texi (freopen): Add documentation of EBUSY failure. [1] http://stackoverflow.com/questions/23440216/race-condition-when-using-dup2
92 lines
3.1 KiB
C
92 lines
3.1 KiB
C
/* Copyright (C) 1993-2017 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<http://www.gnu.org/licenses/>.
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As a special exception, if you link the code in this file with
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files compiled with a GNU compiler to produce an executable,
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that does not cause the resulting executable to be covered by
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the GNU Lesser General Public License. This exception does not
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however invalidate any other reasons why the executable file
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might be covered by the GNU Lesser General Public License.
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This exception applies to code released by its copyright holders
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in files containing the exception. */
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#include "libioP.h"
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#include "stdio.h"
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#include <fcntl.h>
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#include <stdlib.h>
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#include <unistd.h>
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#include <fd_to_filename.h>
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#include <kernel-features.h>
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FILE *
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freopen64 (const char *filename, const char *mode, FILE *fp)
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{
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FILE *result;
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CHECK_FILE (fp, NULL);
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if (!(fp->_flags & _IO_IS_FILEBUF))
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return NULL;
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_IO_acquire_lock (fp);
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int fd = _IO_fileno (fp);
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const char *gfilename = (filename == NULL && fd >= 0
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? fd_to_filename (fd) : filename);
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fp->_flags2 |= _IO_FLAGS2_NOCLOSE;
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_IO_file_close_it (fp);
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_IO_JUMPS_FILE_plus (fp) = &_IO_file_jumps;
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if (_IO_vtable_offset (fp) == 0 && fp->_wide_data != NULL)
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fp->_wide_data->_wide_vtable = &_IO_wfile_jumps;
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result = _IO_file_fopen (fp, gfilename, mode, 0);
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fp->_flags2 &= ~_IO_FLAGS2_NOCLOSE;
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if (result != NULL)
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result = __fopen_maybe_mmap (result);
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if (result != NULL)
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{
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/* unbound stream orientation */
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result->_mode = 0;
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if (fd != -1 && _IO_fileno (result) != fd)
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{
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/* At this point we have both file descriptors already allocated,
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so __dup3 will not fail with EBADF, EINVAL, or EMFILE. But
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we still need to check for EINVAL and, due Linux internal
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implementation, EBUSY. It is because on how it internally opens
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the file by splitting the buffer allocation operation and VFS
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opening (a dup operation may run when a file is still pending
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'install' on VFS). */
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if (__dup3 (_IO_fileno (result), fd,
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(result->_flags2 & _IO_FLAGS2_CLOEXEC) != 0
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? O_CLOEXEC : 0) == -1)
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{
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_IO_file_close_it (result);
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result = NULL;
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goto end;
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}
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__close (_IO_fileno (result));
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_IO_fileno (result) = fd;
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}
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}
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else if (fd != -1)
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__close (fd);
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end:
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if (filename == NULL)
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free ((char *) gfilename);
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_IO_release_lock (fp);
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return result;
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}
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