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/* Invoke popen, but avoid some glitches.
Copyright (C) 2009-2021 Free Software Foundation, Inc.
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3 of the License, or
(at your option) any later version.
This program 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 General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <https://www.gnu.org/licenses/>. */
/* Written by Eric Blake. */
#include <config.h>
#include "stdio-safer.h"
#include <errno.h>
#include <fcntl.h>
#include <unistd.h>
/* Like popen, but do not return stdin, stdout, or stderr. */
FILE *
popen_safer (char const *cmd, char const *mode)
{
/* Unfortunately, we cannot use the fopen_safer approach of using
fdopen (dup_safer (fileno (popen (cmd, mode)))), because stdio
libraries maintain hidden state tying the original fd to the pid
to wait on when using pclose (this hidden state is also used to
avoid fd leaks in subsequent popen calls). So, we instead
guarantee that all standard streams are open prior to the popen
call (even though this puts more pressure on open fds), so that
the original fd created by popen is safe. */
FILE *fp;
int fd = open ("/dev/null", O_RDONLY | O_CLOEXEC);
if (0 <= fd && fd <= STDERR_FILENO)
{
/* Maximum recursion depth is 3. */
int saved_errno;
fp = popen_safer (cmd, mode);
saved_errno = errno;
close (fd);
errno = saved_errno;
}
else
{
/* Either all fd's are tied up, or fd is safe and the real popen
will reuse it. */
close (fd);
fp = popen (cmd, mode);
}
return fp;
}
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