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annotate lib/popen-safer.c @ 40196:e63f5d3edab5

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relocatable-prog: Update documentation. * doc/relocatable-maint.texi (Supporting Relocation): Update to match the recent changes.
author Bruno Haible <bruno@clisp.org>
date Sun, 24 Feb 2019 01:49:15 +0100
parents b06060465f09
children
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1 /* Invoke popen, but avoid some glitches.
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2
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b06060465f09 maint: Run 'make update-copyright'
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3 Copyright (C) 2009-2019 Free Software Foundation, Inc.
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4
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5 This program is free software: you can redistribute it and/or modify
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6 it under the terms of the GNU General Public License as published by
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7 the Free Software Foundation; either version 3 of the License, or
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8 (at your option) any later version.
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9
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10 This program is distributed in the hope that it will be useful,
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11 but WITHOUT ANY WARRANTY; without even the implied warranty of
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12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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13 GNU General Public License for more details.
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14
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15 You should have received a copy of the GNU General Public License
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16 along with this program. If not, see <https://www.gnu.org/licenses/>. */
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17
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18 /* Written by Eric Blake. */
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19
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20 #include <config.h>
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21
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22 #include "stdio-safer.h"
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23
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24 #include <errno.h>
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25 #include <fcntl.h>
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26 #include <unistd.h>
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27
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28 /* Like popen, but do not return stdin, stdout, or stderr. */
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29
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30 FILE *
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31 popen_safer (char const *cmd, char const *mode)
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32 {
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33 /* Unfortunately, we cannot use the fopen_safer approach of using
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34 fdopen (dup_safer (fileno (popen (cmd, mode)))), because stdio
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35 libraries maintain hidden state tying the original fd to the pid
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36 to wait on when using pclose (this hidden state is also used to
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37 avoid fd leaks in subsequent popen calls). So, we instead
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38 guarantee that all standard streams are open prior to the popen
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39 call (even though this puts more pressure on open fds), so that
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40 the original fd created by popen is safe. */
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41 FILE *fp;
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42 int fd = open ("/dev/null", O_RDONLY | O_CLOEXEC);
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43 if (0 <= fd && fd <= STDERR_FILENO)
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44 {
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45 /* Maximum recursion depth is 3. */
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46 int saved_errno;
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47 fp = popen_safer (cmd, mode);
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48 saved_errno = errno;
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49 close (fd);
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50 errno = saved_errno;
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51 }
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52 else
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53 {
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54 /* Either all fd's are tied up, or fd is safe and the real popen
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55 will reuse it. */
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56 close (fd);
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57 fp = popen (cmd, mode);
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58 }
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59 return fp;
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60 }