1 /* Open a descriptor to a file.
2 Copyright (C) 2007-2023 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 2.1 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 Bruno Haible <bruno@clisp.org>, 2007. */
18
19 /* If the user's config.h happens to include <fcntl.h>, let it include only
20 the system's <fcntl.h> here, so that orig_open doesn't recurse to
21 rpl_open. */
22 #define __need_system_fcntl_h
23 #include <config.h>
24
25 /* Get the original definition of open. It might be defined as a macro. */
26 #include <fcntl.h>
27 #include <sys/types.h>
28 #undef __need_system_fcntl_h
29
30 static int
31 orig_open (const char *filename, int flags, mode_t mode)
32 {
33 #if defined _WIN32 && !defined __CYGWIN__
34 return _open (filename, flags, mode);
35 #else
36 return open (filename, flags, mode);
37 #endif
38 }
39
40 /* Specification. */
41 /* Write "fcntl.h" here, not <fcntl.h>, otherwise OSF/1 5.1 DTK cc eliminates
42 this include because of the preliminary #include <fcntl.h> above. */
43 #include "fcntl.h"
44
45 #include "cloexec.h"
46
47 #include <errno.h>
48 #include <stdarg.h>
49 #include <string.h>
50 #include <sys/types.h>
51 #include <sys/stat.h>
52 #include <unistd.h>
53
54 #ifndef REPLACE_OPEN_DIRECTORY
55 # define REPLACE_OPEN_DIRECTORY 0
56 #endif
57
58 int
59 open (const char *filename, int flags, ...)
60 {
61 /* 0 = unknown, 1 = yes, -1 = no. */
62 #if GNULIB_defined_O_CLOEXEC
63 int have_cloexec = -1;
64 #else
65 static int have_cloexec;
66 #endif
67
68 mode_t mode;
69 int fd;
70
71 mode = 0;
72 if (flags & O_CREAT)
73 {
74 va_list arg;
75 va_start (arg, flags);
76
77 /* We have to use PROMOTED_MODE_T instead of mode_t, otherwise GCC 4
78 creates crashing code when 'mode_t' is smaller than 'int'. */
79 mode = va_arg (arg, PROMOTED_MODE_T);
80
81 va_end (arg);
82 }
83
84 #if GNULIB_defined_O_NONBLOCK
85 /* The only known platform that lacks O_NONBLOCK is mingw, but it
86 also lacks named pipes and Unix sockets, which are the only two
87 file types that require non-blocking handling in open().
88 Therefore, it is safe to ignore O_NONBLOCK here. It is handy
89 that mingw also lacks openat(), so that is also covered here. */
90 flags &= ~O_NONBLOCK;
91 #endif
92
93 #if defined _WIN32 && ! defined __CYGWIN__
94 if (strcmp (filename, "/dev/null") == 0)
95 filename = "NUL";
96 #endif
97
98 #if OPEN_TRAILING_SLASH_BUG
99 /* Fail if one of O_CREAT, O_WRONLY, O_RDWR is specified and the filename
100 ends in a slash, as POSIX says such a filename must name a directory
101 <https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap04.html#tag_04_13>:
102 "A pathname that contains at least one non-<slash> character and that
103 ends with one or more trailing <slash> characters shall not be resolved
104 successfully unless the last pathname component before the trailing
105 <slash> characters names an existing directory"
106 If the named file already exists as a directory, then
107 - if O_CREAT is specified, open() must fail because of the semantics
108 of O_CREAT,
109 - if O_WRONLY or O_RDWR is specified, open() must fail because POSIX
110 <https://pubs.opengroup.org/onlinepubs/9699919799/functions/open.html>
111 says that it fails with errno = EISDIR in this case.
112 If the named file does not exist or does not name a directory, then
113 - if O_CREAT is specified, open() must fail since open() cannot create
114 directories,
115 - if O_WRONLY or O_RDWR is specified, open() must fail because the
116 file does not contain a '.' directory. */
117 if ((flags & O_CREAT)
118 || (flags & O_ACCMODE) == O_RDWR
119 || (flags & O_ACCMODE) == O_WRONLY)
120 {
121 size_t len = strlen (filename);
122 if (len > 0 && filename[len - 1] == '/')
123 {
124 errno = EISDIR;
125 return -1;
126 }
127 }
128 #endif
129
130 fd = orig_open (filename,
131 flags & ~(have_cloexec < 0 ? O_CLOEXEC : 0), mode);
132
133 if (flags & O_CLOEXEC)
134 {
135 if (! have_cloexec)
136 {
137 if (0 <= fd)
138 have_cloexec = 1;
139 else if (errno == EINVAL)
140 {
141 fd = orig_open (filename, flags & ~O_CLOEXEC, mode);
142 have_cloexec = -1;
143 }
144 }
145 if (have_cloexec < 0 && 0 <= fd)
146 set_cloexec_flag (fd, true);
147 }
148
149
150 #if REPLACE_FCHDIR
151 /* Implementing fchdir and fdopendir requires the ability to open a
152 directory file descriptor. If open doesn't support that (as on
153 mingw), we use a dummy file that behaves the same as directories
154 on Linux (ie. always reports EOF on attempts to read()), and
155 override fstat() in fchdir.c to hide the fact that we have a
156 dummy. */
157 if (REPLACE_OPEN_DIRECTORY && fd < 0 && errno == EACCES
158 && ((flags & O_ACCMODE) == O_RDONLY
159 || (O_SEARCH != O_RDONLY && (flags & O_ACCMODE) == O_SEARCH)))
160 {
161 struct stat statbuf;
162 if (stat (filename, &statbuf) == 0 && S_ISDIR (statbuf.st_mode))
163 {
164 /* Maximum recursion depth of 1. */
165 fd = open ("/dev/null", flags, mode);
166 if (0 <= fd)
167 fd = _gl_register_fd (fd, filename);
168 }
169 else
170 errno = EACCES;
171 }
172 #endif
173
174 #if OPEN_TRAILING_SLASH_BUG
175 /* If the filename ends in a slash and fd does not refer to a directory,
176 then fail.
177 Rationale: POSIX says such a filename must name a directory
178 <https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap04.html#tag_04_13>:
179 "A pathname that contains at least one non-<slash> character and that
180 ends with one or more trailing <slash> characters shall not be resolved
181 successfully unless the last pathname component before the trailing
182 <slash> characters names an existing directory"
183 If the named file without the slash is not a directory, open() must fail
184 with ENOTDIR. */
185 if (fd >= 0)
186 {
187 /* We know len is positive, since open did not fail with ENOENT. */
188 size_t len = strlen (filename);
189 if (filename[len - 1] == '/')
190 {
191 struct stat statbuf;
192
193 if (fstat (fd, &statbuf) >= 0 && !S_ISDIR (statbuf.st_mode))
194 {
195 close (fd);
196 errno = ENOTDIR;
197 return -1;
198 }
199 }
200 }
201 #endif
202
203 #if REPLACE_FCHDIR
204 if (!REPLACE_OPEN_DIRECTORY && 0 <= fd)
205 fd = _gl_register_fd (fd, filename);
206 #endif
207
208 return fd;
209 }