1 /* Invoke popen, but avoid some glitches. 2 3 Copyright (C) 2009-2021 Free Software Foundation, Inc. 4 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. 9 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. 14 15 You should have received a copy of the GNU General Public License 16 along with this program. If not, see <https://www.gnu.org/licenses/>. */ 17 18 /* Written by Eric Blake. */ 19 20 #include <config.h> 21 22 #include "stdio-safer.h" 23 24 #include <errno.h> 25 #include <fcntl.h> 26 #include <unistd.h> 27 28 /* Like popen, but do not return stdin, stdout, or stderr. */ 29 30 FILE * 31 popen_safer (char const *cmd, char const *mode) /* */ 32 { 33 /* Unfortunately, we cannot use the fopen_safer approach of using 34 fdopen (dup_safer (fileno (popen (cmd, mode)))), because stdio 35 libraries maintain hidden state tying the original fd to the pid 36 to wait on when using pclose (this hidden state is also used to 37 avoid fd leaks in subsequent popen calls). So, we instead 38 guarantee that all standard streams are open prior to the popen 39 call (even though this puts more pressure on open fds), so that 40 the original fd created by popen is safe. */ 41 FILE *fp; 42 int fd = open ("/dev/null", O_RDONLY | O_CLOEXEC); 43 if (0 <= fd && fd <= STDERR_FILENO) 44 { 45 /* Maximum recursion depth is 3. */ 46 int saved_errno; 47 fp = popen_safer (cmd, mode); 48 saved_errno = errno; 49 close (fd); 50 errno = saved_errno; 51 } 52 else 53 { 54 /* Either all fd's are tied up, or fd is safe and the real popen 55 will reuse it. */ 56 close (fd); 57 fp = popen (cmd, mode); 58 } 59 return fp; 60 }