1 /* Change the protections of file relative to an open directory.
2 Copyright (C) 2006, 2009-2023 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 and Paul Eggert */
18
19 /* If the user's config.h happens to include <sys/stat.h>, let it include only
20 the system's <sys/stat.h> here, so that orig_fchmodat doesn't recurse to
21 rpl_fchmodat. */
22 #define __need_system_sys_stat_h
23 #include <config.h>
24
25 /* Specification. */
26 #include <sys/stat.h>
27 #undef __need_system_sys_stat_h
28
29 #if HAVE_FCHMODAT
30 static int
31 orig_fchmodat (int dir, char const *file, mode_t mode, int flags)
32 {
33 return fchmodat (dir, file, mode, flags);
34 }
35 #endif
36
37 #include <errno.h>
38 #include <fcntl.h>
39 #include <stdio.h>
40 #include <stdlib.h>
41 #include <string.h>
42 #include <unistd.h>
43
44 #ifdef __osf__
45 /* Write "sys/stat.h" here, not <sys/stat.h>, otherwise OSF/1 5.1 DTK cc
46 eliminates this include because of the preliminary #include <sys/stat.h>
47 above. */
48 # include "sys/stat.h"
49 #else
50 # include <sys/stat.h>
51 #endif
52
53 #include <intprops.h>
54
55 /* Invoke chmod or lchmod on FILE, using mode MODE, in the directory
56 open on descriptor FD. If possible, do it without changing the
57 working directory. Otherwise, resort to using save_cwd/fchdir,
58 then (chmod|lchmod)/restore_cwd. If either the save_cwd or the
59 restore_cwd fails, then give a diagnostic and exit nonzero.
60 Note that an attempt to use a FLAG value of AT_SYMLINK_NOFOLLOW
61 on a system without lchmod support causes this function to fail. */
62
63 #if HAVE_FCHMODAT
64 int
65 fchmodat (int dir, char const *file, mode_t mode, int flags)
66 {
67 # if HAVE_NEARLY_WORKING_FCHMODAT
68 /* Correct the trailing slash handling. */
69 size_t len = strlen (file);
70 if (len && file[len - 1] == '/')
71 {
72 struct stat st;
73 if (fstatat (dir, file, &st, flags & AT_SYMLINK_NOFOLLOW) < 0)
74 return -1;
75 if (!S_ISDIR (st.st_mode))
76 {
77 errno = ENOTDIR;
78 return -1;
79 }
80 }
81 # endif
82
83 # if NEED_FCHMODAT_NONSYMLINK_FIX
84 if (flags == AT_SYMLINK_NOFOLLOW)
85 {
86 # if HAVE_READLINKAT
87 char readlink_buf[1];
88
89 # ifdef O_PATH
90 /* Open a file descriptor with O_NOFOLLOW, to make sure we don't
91 follow symbolic links, if /proc is mounted. O_PATH is used to
92 avoid a failure if the file is not readable.
93 Cf. <https://sourceware.org/bugzilla/show_bug.cgi?id=14578> */
94 int fd = openat (dir, file, O_PATH | O_NOFOLLOW | O_CLOEXEC);
95 if (fd < 0)
96 return fd;
97
98 int err;
99 if (0 <= readlinkat (fd, "", readlink_buf, sizeof readlink_buf))
100 err = EOPNOTSUPP;
101 else if (errno == EINVAL)
102 {
103 static char const fmt[] = "/proc/self/fd/%d";
104 char buf[sizeof fmt - sizeof "%d" + INT_BUFSIZE_BOUND (int)];
105 sprintf (buf, fmt, fd);
106 err = chmod (buf, mode) == 0 ? 0 : errno == ENOENT ? -1 : errno;
107 }
108 else
109 err = errno == ENOENT ? -1 : errno;
110
111 close (fd);
112
113 errno = err;
114 if (0 <= err)
115 return err == 0 ? 0 : -1;
116 # endif
117
118 /* O_PATH + /proc is not supported. */
119
120 if (0 <= readlinkat (dir, file, readlink_buf, sizeof readlink_buf))
121 {
122 errno = EOPNOTSUPP;
123 return -1;
124 }
125 # endif
126
127 /* Fall back on orig_fchmodat with no flags, despite a possible race. */
128 flags = 0;
129 }
130 # endif
131
132 return orig_fchmodat (dir, file, mode, flags);
133 }
134 #else
135 # define AT_FUNC_NAME fchmodat
136 # define AT_FUNC_F1 lchmod
137 # define AT_FUNC_F2 chmod
138 # define AT_FUNC_USE_F1_COND AT_SYMLINK_NOFOLLOW
139 # define AT_FUNC_POST_FILE_PARAM_DECLS , mode_t mode, int flag
140 # define AT_FUNC_POST_FILE_ARGS , mode
141 # include "at-func.c"
142 #endif