1 /* Invoke opendir, 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 "dirent-safer.h" 23 24 #include <errno.h> 25 #include <fcntl.h> 26 #include <unistd.h> 27 28 /* Like opendir, but do not clobber stdin, stdout, or stderr. */ 29 30 DIR * 31 opendir_safer (char const *name) /* */ 32 { 33 DIR *dp = opendir (name); 34 35 if (dp) 36 { 37 int fd = dirfd (dp); 38 39 if (0 <= fd && fd <= STDERR_FILENO) 40 { 41 /* If fdopendir is native (as on Linux), then it is safe to 42 assume dirfd(fdopendir(n))==n. If we are using the 43 gnulib module fdopendir, then this guarantee is not met, 44 but fdopendir recursively calls opendir_safer up to 3 45 times to at least get a safe fd. If fdopendir is not 46 present but dirfd is accurate (as on cygwin 1.5.x), then 47 we recurse up to 3 times ourselves. Finally, if dirfd 48 always fails (as on mingw), then we are already safe. */ 49 DIR *newdp; 50 int e; 51 #if HAVE_FDOPENDIR || GNULIB_FDOPENDIR 52 int f = fcntl (fd, F_DUPFD_CLOEXEC, STDERR_FILENO + 1); 53 if (f < 0) 54 { 55 e = errno; 56 newdp = NULL; 57 } 58 else 59 { 60 newdp = fdopendir (f); 61 e = errno; 62 if (! newdp) 63 close (f); 64 } 65 #else /* !FDOPENDIR */ 66 newdp = opendir_safer (name); 67 e = errno; 68 #endif 69 closedir (dp); 70 errno = e; 71 dp = newdp; 72 } 73 } 74 75 return dp; 76 }