1 /* Invoke freopen, but avoid some glitches.
3 Copyright (C) 2009-2013 Free Software Foundation, Inc.
5 This program is free software: you can redistribute it and/or modify
6 it under the terms of the GNU General Public License as published by
7 the Free Software Foundation; either version 3 of the License, or
8 (at your option) any later version.
10 This program is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13 GNU General Public License for more details.
15 You should have received a copy of the GNU General Public License
16 along with this program. If not, see <http://www.gnu.org/licenses/>. */
18 /* Written by Eric Blake. */
22 #include "stdio-safer.h"
29 /* Guarantee that FD is open; all smaller FDs must already be open.
30 Return true if successful. */
34 int value = open ("/dev/null", O_RDONLY);
40 errno = EBADF; /* Unexpected; this is as good as anything else. */
47 /* Like freopen, but guarantee that reopening stdin, stdout, or stderr
48 preserves the invariant that STDxxx_FILENO==fileno(stdxxx), and
49 that no other stream will interfere with the standard streams.
50 This is necessary because most freopen implementations will change
51 the associated fd of a stream to the lowest available slot. */
54 freopen_safer (char const *name, char const *mode, FILE *f)
56 /* Unfortunately, we cannot use the fopen_safer approach of using
57 fdopen (dup_safer (fileno (freopen (cmd, mode, f)))), because we
58 need to return f itself. The implementation of freopen(NULL,m,f)
59 is system-dependent, so the best we can do is guarantee that all
60 lower-valued standard fds are open prior to the freopen call,
61 even though this puts more pressure on open fds. */
62 bool protect_in = false;
63 bool protect_out = false;
64 bool protect_err = false;
69 default: /* -1 or not a standard stream. */
70 if (dup2 (STDERR_FILENO, STDERR_FILENO) != STDERR_FILENO)
74 if (dup2 (STDOUT_FILENO, STDOUT_FILENO) != STDOUT_FILENO)
78 if (dup2 (STDIN_FILENO, STDIN_FILENO) != STDIN_FILENO)
82 /* Nothing left to protect. */
85 if (protect_in && !protect_fd (STDIN_FILENO))
87 else if (protect_out && !protect_fd (STDOUT_FILENO))
89 else if (protect_err && !protect_fd (STDERR_FILENO))
92 f = freopen (name, mode, f);
95 close (STDERR_FILENO);
97 close (STDOUT_FILENO);