61 lines
2.0 KiB
C
61 lines
2.0 KiB
C
/* Invoke popen, but avoid some glitches.
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Copyright (C) 2009-2024 Free Software Foundation, Inc.
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This program is free software: you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation, either version 3 of the License, or
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(at your option) any later version.
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This program 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
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <https://www.gnu.org/licenses/>. */
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/* Written by Eric Blake. */
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#include <config.h>
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#include "stdio-safer.h"
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#include <errno.h>
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#include <fcntl.h>
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#include <unistd.h>
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/* Like popen, but do not return stdin, stdout, or stderr. */
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FILE *
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popen_safer (char const *cmd, char const *mode)
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{
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/* Unfortunately, we cannot use the fopen_safer approach of using
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fdopen (dup_safer (fileno (popen (cmd, mode)))), because stdio
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libraries maintain hidden state tying the original fd to the pid
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to wait on when using pclose (this hidden state is also used to
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avoid fd leaks in subsequent popen calls). So, we instead
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guarantee that all standard streams are open prior to the popen
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call (even though this puts more pressure on open fds), so that
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the original fd created by popen is safe. */
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FILE *fp;
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int fd = open ("/dev/null", O_RDONLY | O_CLOEXEC);
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if (0 <= fd && fd <= STDERR_FILENO)
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{
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/* Maximum recursion depth is 3. */
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int saved_errno;
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fp = popen_safer (cmd, mode);
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saved_errno = errno;
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close (fd);
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errno = saved_errno;
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}
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else
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{
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/* Either all fd's are tied up, or fd is safe and the real popen
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will reuse it. */
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close (fd);
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fp = popen (cmd, mode);
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}
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return fp;
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}
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