1 /* Open a stream to a sub-process. 2 Copyright (C) 2009-2021 Free Software Foundation, Inc. 3 4 This file is free software: you can redistribute it and/or modify 5 it under the terms of the GNU Lesser General Public License as 6 published by the Free Software Foundation; either version 3 of the 7 License, or (at your option) any later version. 8 9 This file is distributed in the hope that it will be useful, 10 but WITHOUT ANY WARRANTY; without even the implied warranty of 11 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 12 GNU Lesser General Public License for more details. 13 14 You should have received a copy of the GNU Lesser General Public License 15 along with this program. If not, see <https://www.gnu.org/licenses/>. */ 16 17 /* Written by Eric Blake <ebb9@byu.net>, 2009. */ 18 19 #include <config.h> 20 21 /* Specification. */ 22 #include <stdio.h> 23 24 #if defined _WIN32 && ! defined __CYGWIN__ 25 /* Native Windows API. */ 26 27 # include <string.h> 28 29 FILE * 30 popen (const char *filename, const char *mode) /* */ 31 { 32 /* Use binary mode by default. */ 33 if (strcmp (mode, "r") == 0) 34 mode = "rb"; 35 else if (strcmp (mode, "w") == 0) 36 mode = "wb"; 37 38 return _popen (filename, mode); 39 } 40 41 #else 42 43 # include <errno.h> 44 # include <fcntl.h> 45 # include <stdlib.h> 46 # include <unistd.h> 47 48 # undef popen 49 50 FILE * 51 rpl_popen (const char *filename, const char *mode) /* */ 52 { 53 /* All other platforms have popen and fcntl. 54 The bug of the child clobbering its own file descriptors if stdin 55 or stdout was closed in the parent can be worked around by 56 opening those two fds as close-on-exec to begin with. */ 57 /* Cygwin 1.5.x also has a bug where the popen fd is improperly 58 marked close-on-exec, and if the application undoes this, then 59 the fd leaks into subsequent popen calls. We could work around 60 this by maintaining a list of all fd's opened by popen, and 61 temporarily marking them cloexec around the real popen call, but 62 we would also have to override pclose, and the bookkeeping seems 63 extreme given that cygwin 1.7 no longer has the bug. */ 64 FILE *result; 65 int cloexec0 = fcntl (STDIN_FILENO, F_GETFD); 66 int cloexec1 = fcntl (STDOUT_FILENO, F_GETFD); 67 int saved_errno; 68 69 /* If either stdin or stdout was closed (that is, fcntl failed), 70 then we open a dummy close-on-exec fd to occupy that slot. That 71 way, popen's internal use of pipe() will not contain either fd 0 72 or 1, overcoming the fact that the child process blindly calls 73 close() on the parent's end of the pipe without first checking 74 whether it is clobbering the fd just placed there via dup2(); the 75 exec will get rid of the dummy fd's in the child. Fortunately, 76 closed stderr in the parent does not cause problems in the 77 child. */ 78 if (cloexec0 < 0) 79 { 80 if (open ("/dev/null", O_RDONLY) != STDIN_FILENO 81 || fcntl (STDIN_FILENO, F_SETFD, 82 fcntl (STDIN_FILENO, F_GETFD) | FD_CLOEXEC) == -1) 83 abort (); 84 } 85 if (cloexec1 < 0) 86 { 87 if (open ("/dev/null", O_RDONLY) != STDOUT_FILENO 88 || fcntl (STDOUT_FILENO, F_SETFD, 89 fcntl (STDOUT_FILENO, F_GETFD) | FD_CLOEXEC) == -1) 90 abort (); 91 } 92 result = popen (filename, mode); 93 /* Now, close any dummy fd's created in the parent. */ 94 saved_errno = errno; 95 if (cloexec0 < 0) 96 close (STDIN_FILENO); 97 if (cloexec1 < 0) 98 close (STDOUT_FILENO); 99 errno = saved_errno; 100 return result; 101 } 102 103 #endif