| 1 | /* provide a replacement fdopendir function |
| 2 | Copyright (C) 2004-2019 Free Software Foundation, Inc. |
| 3 | |
| 4 | This program is free software: you can redistribute it and/or modify |
| 5 | it under the terms of the GNU General Public License as published by |
| 6 | the Free Software Foundation; either version 3 of the License, or |
| 7 | (at your option) any later version. |
| 8 | |
| 9 | This program 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 General Public License for more details. |
| 13 | |
| 14 | You should have received a copy of the GNU General Public License |
| 15 | along with this program. If not, see <https://www.gnu.org/licenses/>. */ |
| 16 | |
| 17 | /* written by Jim Meyering */ |
| 18 | |
| 19 | #include <config.h> |
| 20 | |
| 21 | #include <dirent.h> |
| 22 | |
| 23 | #include <stdlib.h> |
| 24 | #include <unistd.h> |
| 25 | |
| 26 | #if !HAVE_FDOPENDIR |
| 27 | |
| 28 | # include "openat.h" |
| 29 | # include "openat-priv.h" |
| 30 | # include "save-cwd.h" |
| 31 | |
| 32 | # if GNULIB_DIRENT_SAFER |
| 33 | # include "dirent--.h" |
| 34 | # endif |
| 35 | |
| 36 | # ifndef REPLACE_FCHDIR |
| 37 | # define REPLACE_FCHDIR 0 |
| 38 | # endif |
| 39 | |
| 40 | static DIR *fdopendir_with_dup (int, int, struct saved_cwd const *); |
| 41 | static DIR *fd_clone_opendir (int, struct saved_cwd const *); |
| 42 | |
| 43 | /* Replacement for POSIX fdopendir. |
| 44 | |
| 45 | First, try to simulate it via opendir ("/proc/self/fd/..."). Failing |
| 46 | that, simulate it by using fchdir metadata, or by doing |
| 47 | save_cwd/fchdir/opendir(".")/restore_cwd. |
| 48 | If either the save_cwd or the restore_cwd fails (relatively unlikely), |
| 49 | then give a diagnostic and exit nonzero. |
| 50 | |
| 51 | If successful, the resulting stream is based on FD in |
| 52 | implementations where streams are based on file descriptors and in |
| 53 | applications where no other thread or signal handler allocates or |
| 54 | frees file descriptors. In other cases, consult dirfd on the result |
| 55 | to find out whether FD is still being used. |
| 56 | |
| 57 | Otherwise, this function works just like POSIX fdopendir. |
| 58 | |
| 59 | W A R N I N G: |
| 60 | |
| 61 | Unlike other fd-related functions, this one places constraints on FD. |
| 62 | If this function returns successfully, FD is under control of the |
| 63 | dirent.h system, and the caller should not close or modify the state of |
| 64 | FD other than by the dirent.h functions. */ |
| 65 | # ifdef __KLIBC__ |
| 66 | # include <InnoTekLIBC/backend.h> |
| 67 | |
| 68 | DIR * |
| 69 | fdopendir (int fd) |
| 70 | { |
| 71 | char path[_MAX_PATH]; |
| 72 | DIR *dirp; |
| 73 | |
| 74 | /* Get a path from fd */ |
| 75 | if (__libc_Back_ioFHToPath (fd, path, sizeof (path))) |
| 76 | return NULL; |
| 77 | |
| 78 | dirp = opendir (path); |
| 79 | if (!dirp) |
| 80 | return NULL; |
| 81 | |
| 82 | /* Unregister fd registered by opendir() */ |
| 83 | _gl_unregister_dirp_fd (dirfd (dirp)); |
| 84 | |
| 85 | /* Register our fd */ |
| 86 | if (_gl_register_dirp_fd (fd, dirp)) |
| 87 | { |
| 88 | int saved_errno = errno; |
| 89 | |
| 90 | closedir (dirp); |
| 91 | |
| 92 | errno = saved_errno; |
| 93 | |
| 94 | dirp = NULL; |
| 95 | } |
| 96 | |
| 97 | return dirp; |
| 98 | } |
| 99 | # else |
| 100 | DIR * |
| 101 | fdopendir (int fd) |
| 102 | { |
| 103 | DIR *dir = fdopendir_with_dup (fd, -1, NULL); |
| 104 | |
| 105 | if (! REPLACE_FCHDIR && ! dir) |
| 106 | { |
| 107 | int saved_errno = errno; |
| 108 | if (EXPECTED_ERRNO (saved_errno)) |
| 109 | { |
| 110 | struct saved_cwd cwd; |
| 111 | if (save_cwd (&cwd) != 0) |
| 112 | openat_save_fail (errno); |
| 113 | dir = fdopendir_with_dup (fd, -1, &cwd); |
| 114 | saved_errno = errno; |
| 115 | free_cwd (&cwd); |
| 116 | errno = saved_errno; |
| 117 | } |
| 118 | } |
| 119 | |
| 120 | return dir; |
| 121 | } |
| 122 | # endif |
| 123 | |
| 124 | /* Like fdopendir, except that if OLDER_DUPFD is not -1, it is known |
| 125 | to be a dup of FD which is less than FD - 1 and which will be |
| 126 | closed by the caller and not otherwise used by the caller. This |
| 127 | function makes sure that FD is closed and all file descriptors less |
| 128 | than FD are open, and then calls fd_clone_opendir on a dup of FD. |
| 129 | That way, barring race conditions, fd_clone_opendir returns a |
| 130 | stream whose file descriptor is FD. |
| 131 | |
| 132 | If REPLACE_FCHDIR or CWD is null, use opendir ("/proc/self/fd/...", |
| 133 | falling back on fchdir metadata. Otherwise, CWD is a saved version |
| 134 | of the working directory; use fchdir/opendir(".")/restore_cwd(CWD). */ |
| 135 | static DIR * |
| 136 | fdopendir_with_dup (int fd, int older_dupfd, struct saved_cwd const *cwd) |
| 137 | { |
| 138 | int dupfd = dup (fd); |
| 139 | if (dupfd < 0 && errno == EMFILE) |
| 140 | dupfd = older_dupfd; |
| 141 | if (dupfd < 0) |
| 142 | return NULL; |
| 143 | else |
| 144 | { |
| 145 | DIR *dir; |
| 146 | int saved_errno; |
| 147 | if (dupfd < fd - 1 && dupfd != older_dupfd) |
| 148 | { |
| 149 | dir = fdopendir_with_dup (fd, dupfd, cwd); |
| 150 | saved_errno = errno; |
| 151 | } |
| 152 | else |
| 153 | { |
| 154 | close (fd); |
| 155 | dir = fd_clone_opendir (dupfd, cwd); |
| 156 | saved_errno = errno; |
| 157 | if (! dir) |
| 158 | { |
| 159 | int fd1 = dup (dupfd); |
| 160 | if (fd1 != fd) |
| 161 | openat_save_fail (fd1 < 0 ? errno : EBADF); |
| 162 | } |
| 163 | } |
| 164 | |
| 165 | if (dupfd != older_dupfd) |
| 166 | close (dupfd); |
| 167 | errno = saved_errno; |
| 168 | return dir; |
| 169 | } |
| 170 | } |
| 171 | |
| 172 | /* Like fdopendir, except the result controls a clone of FD. It is |
| 173 | the caller's responsibility both to close FD and (if the result is |
| 174 | not null) to closedir the result. */ |
| 175 | static DIR * |
| 176 | fd_clone_opendir (int fd, struct saved_cwd const *cwd) |
| 177 | { |
| 178 | if (REPLACE_FCHDIR || ! cwd) |
| 179 | { |
| 180 | DIR *dir = NULL; |
| 181 | int saved_errno = EOPNOTSUPP; |
| 182 | char buf[OPENAT_BUFFER_SIZE]; |
| 183 | char *proc_file = openat_proc_name (buf, fd, "."); |
| 184 | if (proc_file) |
| 185 | { |
| 186 | dir = opendir (proc_file); |
| 187 | saved_errno = errno; |
| 188 | if (proc_file != buf) |
| 189 | free (proc_file); |
| 190 | } |
| 191 | # if REPLACE_FCHDIR |
| 192 | if (! dir && EXPECTED_ERRNO (saved_errno)) |
| 193 | { |
| 194 | char const *name = _gl_directory_name (fd); |
| 195 | DIR *dp = name ? opendir (name) : NULL; |
| 196 | |
| 197 | /* The caller has done an elaborate dance to arrange for opendir to |
| 198 | consume just the right file descriptor. If dirfd returns -1, |
| 199 | though, we're on a system like mingw where opendir does not |
| 200 | consume a file descriptor. Consume it via 'dup' instead. */ |
| 201 | if (dp && dirfd (dp) < 0) |
| 202 | dup (fd); |
| 203 | |
| 204 | return dp; |
| 205 | } |
| 206 | # endif |
| 207 | errno = saved_errno; |
| 208 | return dir; |
| 209 | } |
| 210 | else |
| 211 | { |
| 212 | if (fchdir (fd) != 0) |
| 213 | return NULL; |
| 214 | else |
| 215 | { |
| 216 | DIR *dir = opendir ("."); |
| 217 | int saved_errno = errno; |
| 218 | if (restore_cwd (cwd) != 0) |
| 219 | openat_restore_fail (errno); |
| 220 | errno = saved_errno; |
| 221 | return dir; |
| 222 | } |
| 223 | } |
| 224 | } |
| 225 | |
| 226 | #else /* HAVE_FDOPENDIR */ |
| 227 | |
| 228 | # include <errno.h> |
| 229 | # include <sys/stat.h> |
| 230 | |
| 231 | # undef fdopendir |
| 232 | |
| 233 | /* Like fdopendir, but work around GNU/Hurd bug by validating FD. */ |
| 234 | |
| 235 | DIR * |
| 236 | rpl_fdopendir (int fd) |
| 237 | { |
| 238 | struct stat st; |
| 239 | if (fstat (fd, &st)) |
| 240 | return NULL; |
| 241 | if (!S_ISDIR (st.st_mode)) |
| 242 | { |
| 243 | errno = ENOTDIR; |
| 244 | return NULL; |
| 245 | } |
| 246 | return fdopendir (fd); |
| 247 | } |
| 248 | |
| 249 | #endif /* HAVE_FDOPENDIR */ |