1 /* Open a descriptor to a file.
2    Copyright (C) 2007-2020 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 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
orig_open(const char * filename,int flags,mode_t mode)31 orig_open (const char *filename, int flags, mode_t mode)
32 {
33   return open (filename, flags, mode);
34 }
35 
36 /* Specification.  */
37 /* Write "fcntl.h" here, not <fcntl.h>, otherwise OSF/1 5.1 DTK cc eliminates
38    this include because of the preliminary #include <fcntl.h> above.  */
39 #include "fcntl.h"
40 
41 #include "cloexec.h"
42 
43 #include <errno.h>
44 #include <stdarg.h>
45 #include <string.h>
46 #include <sys/types.h>
47 #include <sys/stat.h>
48 #include <unistd.h>
49 
50 #ifndef REPLACE_OPEN_DIRECTORY
51 # define REPLACE_OPEN_DIRECTORY 0
52 #endif
53 
54 int
open(const char * filename,int flags,...)55 open (const char *filename, int flags, ...)
56 {
57   /* 0 = unknown, 1 = yes, -1 = no.  */
58 #if GNULIB_defined_O_CLOEXEC
59   int have_cloexec = -1;
60 #else
61   static int have_cloexec;
62 #endif
63 
64   mode_t mode;
65   int fd;
66 
67   mode = 0;
68   if (flags & O_CREAT)
69     {
70       va_list arg;
71       va_start (arg, flags);
72 
73       /* We have to use PROMOTED_MODE_T instead of mode_t, otherwise GCC 4
74          creates crashing code when 'mode_t' is smaller than 'int'.  */
75       mode = va_arg (arg, PROMOTED_MODE_T);
76 
77       va_end (arg);
78     }
79 
80 #if GNULIB_defined_O_NONBLOCK
81   /* The only known platform that lacks O_NONBLOCK is mingw, but it
82      also lacks named pipes and Unix sockets, which are the only two
83      file types that require non-blocking handling in open().
84      Therefore, it is safe to ignore O_NONBLOCK here.  It is handy
85      that mingw also lacks openat(), so that is also covered here.  */
86   flags &= ~O_NONBLOCK;
87 #endif
88 
89 #if defined _WIN32 && ! defined __CYGWIN__
90   if (strcmp (filename, "/dev/null") == 0)
91     filename = "NUL";
92 #endif
93 
94 #if OPEN_TRAILING_SLASH_BUG
95   /* Fail if one of O_CREAT, O_WRONLY, O_RDWR is specified and the filename
96      ends in a slash, as POSIX says such a filename must name a directory
97      <https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap04.html#tag_04_13>:
98        "A pathname that contains at least one non-<slash> character and that
99         ends with one or more trailing <slash> characters shall not be resolved
100         successfully unless the last pathname component before the trailing
101         <slash> characters names an existing directory"
102      If the named file already exists as a directory, then
103        - if O_CREAT is specified, open() must fail because of the semantics
104          of O_CREAT,
105        - if O_WRONLY or O_RDWR is specified, open() must fail because POSIX
106          <https://pubs.opengroup.org/onlinepubs/9699919799/functions/open.html>
107          says that it fails with errno = EISDIR in this case.
108      If the named file does not exist or does not name a directory, then
109        - if O_CREAT is specified, open() must fail since open() cannot create
110          directories,
111        - if O_WRONLY or O_RDWR is specified, open() must fail because the
112          file does not contain a '.' directory.  */
113   if ((flags & O_CREAT)
114       || (flags & O_ACCMODE) == O_RDWR
115       || (flags & O_ACCMODE) == O_WRONLY)
116     {
117       size_t len = strlen (filename);
118       if (len > 0 && filename[len - 1] == '/')
119         {
120           errno = EISDIR;
121           return -1;
122         }
123     }
124 #endif
125 
126   fd = orig_open (filename,
127                   flags & ~(have_cloexec < 0 ? O_CLOEXEC : 0), mode);
128 
129   if (flags & O_CLOEXEC)
130     {
131       if (! have_cloexec)
132         {
133           if (0 <= fd)
134             have_cloexec = 1;
135           else if (errno == EINVAL)
136             {
137               fd = orig_open (filename, flags & ~O_CLOEXEC, mode);
138               have_cloexec = -1;
139             }
140         }
141       if (have_cloexec < 0 && 0 <= fd)
142         set_cloexec_flag (fd, true);
143     }
144 
145 
146 #if REPLACE_FCHDIR
147   /* Implementing fchdir and fdopendir requires the ability to open a
148      directory file descriptor.  If open doesn't support that (as on
149      mingw), we use a dummy file that behaves the same as directories
150      on Linux (ie. always reports EOF on attempts to read()), and
151      override fstat() in fchdir.c to hide the fact that we have a
152      dummy.  */
153   if (REPLACE_OPEN_DIRECTORY && fd < 0 && errno == EACCES
154       && ((flags & O_ACCMODE) == O_RDONLY
155           || (O_SEARCH != O_RDONLY && (flags & O_ACCMODE) == O_SEARCH)))
156     {
157       struct stat statbuf;
158       if (stat (filename, &statbuf) == 0 && S_ISDIR (statbuf.st_mode))
159         {
160           /* Maximum recursion depth of 1.  */
161           fd = open ("/dev/null", flags, mode);
162           if (0 <= fd)
163             fd = _gl_register_fd (fd, filename);
164         }
165       else
166         errno = EACCES;
167     }
168 #endif
169 
170 #if OPEN_TRAILING_SLASH_BUG
171   /* If the filename ends in a slash and fd does not refer to a directory,
172      then fail.
173      Rationale: POSIX says such a filename must name a directory
174      <https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap04.html#tag_04_13>:
175        "A pathname that contains at least one non-<slash> character and that
176         ends with one or more trailing <slash> characters shall not be resolved
177         successfully unless the last pathname component before the trailing
178         <slash> characters names an existing directory"
179      If the named file without the slash is not a directory, open() must fail
180      with ENOTDIR.  */
181   if (fd >= 0)
182     {
183       /* We know len is positive, since open did not fail with ENOENT.  */
184       size_t len = strlen (filename);
185       if (filename[len - 1] == '/')
186         {
187           struct stat statbuf;
188 
189           if (fstat (fd, &statbuf) >= 0 && !S_ISDIR (statbuf.st_mode))
190             {
191               close (fd);
192               errno = ENOTDIR;
193               return -1;
194             }
195         }
196     }
197 #endif
198 
199 #if REPLACE_FCHDIR
200   if (!REPLACE_OPEN_DIRECTORY && 0 <= fd)
201     fd = _gl_register_fd (fd, filename);
202 #endif
203 
204   return fd;
205 }
206