1 /* This function serves as replacement for a missing fchownat function,
2 as well as a workaround for the fchownat bug in glibc-2.4:
3 <https://lists.ubuntu.com/archives/ubuntu-users/2006-September/093218.html>
4 when the buggy fchownat-with-AT_SYMLINK_NOFOLLOW operates on a symlink, it
5 mistakenly affects the symlink referent, rather than the symlink itself.
6
7 Copyright (C) 2006-2007, 2009-2023 Free Software Foundation, Inc.
8
9 This program is free software: you can redistribute it and/or modify
10 it under the terms of the GNU General Public License as published by
11 the Free Software Foundation, either version 3 of the License, or
12 (at your option) any later version.
13
14 This program is distributed in the hope that it will be useful,
15 but WITHOUT ANY WARRANTY; without even the implied warranty of
16 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
17 GNU General Public License for more details.
18
19 You should have received a copy of the GNU General Public License
20 along with this program. If not, see <https://www.gnu.org/licenses/>. */
21
22 /* written by Jim Meyering */
23
24 #include <config.h>
25
26 /* Specification. */
27 #include <unistd.h>
28
29 #include <errno.h>
30 #include <stdlib.h>
31 #include <string.h>
32
33 #include "openat.h"
34
35 #if !HAVE_FCHOWNAT
36
37 /* Replacement for Solaris' function by the same name.
38 Invoke chown or lchown on file, FILE, using OWNER and GROUP, in the
39 directory open on descriptor FD. If FLAG is AT_SYMLINK_NOFOLLOW, then
40 use lchown, otherwise, use chown. If possible, do it without changing
41 the working directory. Otherwise, resort to using save_cwd/fchdir,
42 then (chown|lchown)/restore_cwd. If either the save_cwd or the
43 restore_cwd fails, then give a diagnostic and exit nonzero. */
44
45 # define AT_FUNC_NAME fchownat
46 # define AT_FUNC_F1 lchown
47 # define AT_FUNC_F2 chown
48 # define AT_FUNC_USE_F1_COND AT_SYMLINK_NOFOLLOW
49 # define AT_FUNC_POST_FILE_PARAM_DECLS , uid_t owner, gid_t group, int flag
50 # define AT_FUNC_POST_FILE_ARGS , owner, group
51 # include "at-func.c"
52 # undef AT_FUNC_NAME
53 # undef AT_FUNC_F1
54 # undef AT_FUNC_F2
55 # undef AT_FUNC_USE_F1_COND
56 # undef AT_FUNC_POST_FILE_PARAM_DECLS
57 # undef AT_FUNC_POST_FILE_ARGS
58
59 #else /* HAVE_FCHOWNAT */
60
61 # undef fchownat
62
63 # if FCHOWNAT_NOFOLLOW_BUG
64
65 /* Failure to handle AT_SYMLINK_NOFOLLOW requires the /proc/self/fd or
66 fchdir workaround to call lchown for lchownat, but there is no need
67 to penalize chownat. */
68 static int
69 local_lchownat (int fd, char const *file, uid_t owner, gid_t group);
70
71 # define AT_FUNC_NAME local_lchownat
72 # define AT_FUNC_F1 lchown
73 # define AT_FUNC_POST_FILE_PARAM_DECLS , uid_t owner, gid_t group
74 # define AT_FUNC_POST_FILE_ARGS , owner, group
75 # include "at-func.c"
76 # undef AT_FUNC_NAME
77 # undef AT_FUNC_F1
78 # undef AT_FUNC_POST_FILE_PARAM_DECLS
79 # undef AT_FUNC_POST_FILE_ARGS
80
81 # endif
82
83 /* Work around bugs with trailing slash, using the same workarounds as
84 chown and lchown. */
85
86 int
87 rpl_fchownat (int fd, char const *file, uid_t owner, gid_t group, int flag)
88 {
89 # if FCHOWNAT_NOFOLLOW_BUG
90 if (flag == AT_SYMLINK_NOFOLLOW)
91 return local_lchownat (fd, file, owner, group);
92 # endif
93 # if FCHOWNAT_EMPTY_FILENAME_BUG
94 if (file[0] == '\0')
95 {
96 errno = ENOENT;
97 return -1;
98 }
99 # endif
100 # if CHOWN_TRAILING_SLASH_BUG
101 {
102 size_t len = strlen (file);
103 struct stat st;
104 if (len && file[len - 1] == '/')
105 {
106 if (fstatat (fd, file, &st, 0))
107 return -1;
108 if (flag == AT_SYMLINK_NOFOLLOW)
109 return fchownat (fd, file, owner, group, 0);
110 }
111 }
112 # endif
113 return fchownat (fd, file, owner, group, flag);
114 }
115
116 #endif /* HAVE_FCHOWNAT */