1/* provide consistent interface to chown for systems that don't interpret 2 an ID of -1 as meaning `don't change the corresponding ID'. 3 4 Copyright (C) 1997, 2004-2007, 2009-2010 Free Software Foundation, Inc. 5 6 This program is free software: you can redistribute it and/or modify 7 it under the terms of the GNU General Public License as published by 8 the Free Software Foundation; either version 3 of the License, or 9 (at your option) any later version. 10 11 This program is distributed in the hope that it will be useful, 12 but WITHOUT ANY WARRANTY; without even the implied warranty of 13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 14 GNU General Public License for more details. 15 16 You should have received a copy of the GNU General Public License 17 along with this program. If not, see <http://www.gnu.org/licenses/>. */ 18 19/* written by Jim Meyering */ 20 21#include <config.h> 22 23/* Specification. */ 24#include <unistd.h> 25 26#include <errno.h> 27#include <fcntl.h> 28#include <stdbool.h> 29#include <string.h> 30#include <sys/stat.h> 31 32#if !HAVE_CHOWN 33 34/* Simple stub that always fails with ENOSYS, for mingw. */ 35int 36chown (const char *file _GL_UNUSED, uid_t uid _GL_UNUSED, 37 gid_t gid _GL_UNUSED) 38{ 39 errno = ENOSYS; 40 return -1; 41} 42 43#else /* HAVE_CHOWN */ 44 45/* Below we refer to the system's chown(). */ 46# undef chown 47 48/* The results of open() in this file are not used with fchdir, 49 therefore save some unnecessary work in fchdir.c. */ 50# undef open 51# undef close 52 53/* Provide a more-closely POSIX-conforming version of chown on 54 systems with one or both of the following problems: 55 - chown doesn't treat an ID of -1 as meaning 56 `don't change the corresponding ID'. 57 - chown doesn't dereference symlinks. */ 58 59int 60rpl_chown (const char *file, uid_t uid, gid_t gid) 61{ 62 struct stat st; 63 bool stat_valid = false; 64 int result; 65 66# if CHOWN_CHANGE_TIME_BUG 67 if (gid != (gid_t) -1 || uid != (uid_t) -1) 68 { 69 if (stat (file, &st)) 70 return -1; 71 stat_valid = true; 72 } 73# endif 74 75# if CHOWN_FAILS_TO_HONOR_ID_OF_NEGATIVE_ONE 76 if (gid == (gid_t) -1 || uid == (uid_t) -1) 77 { 78 /* Stat file to get id(s) that should remain unchanged. */ 79 if (!stat_valid && stat (file, &st)) 80 return -1; 81 if (gid == (gid_t) -1) 82 gid = st.st_gid; 83 if (uid == (uid_t) -1) 84 uid = st.st_uid; 85 } 86# endif 87 88# if CHOWN_MODIFIES_SYMLINK 89 { 90 /* Handle the case in which the system-supplied chown function 91 does *not* follow symlinks. Instead, it changes permissions 92 on the symlink itself. To work around that, we open the 93 file (but this can fail due to lack of read or write permission) and 94 use fchown on the resulting descriptor. */ 95 int open_flags = O_NONBLOCK | O_NOCTTY; 96 int fd = open (file, O_RDONLY | open_flags); 97 if (0 <= fd 98 || (errno == EACCES 99 && 0 <= (fd = open (file, O_WRONLY | open_flags)))) 100 { 101 int saved_errno; 102 bool fchown_socket_failure; 103 104 result = fchown (fd, uid, gid); 105 saved_errno = errno; 106 107 /* POSIX says fchown can fail with errno == EINVAL on sockets 108 and pipes, so fall back on chown in that case. */ 109 fchown_socket_failure = 110 (result != 0 && saved_errno == EINVAL 111 && fstat (fd, &st) == 0 112 && (S_ISFIFO (st.st_mode) || S_ISSOCK (st.st_mode))); 113 114 close (fd); 115 116 if (! fchown_socket_failure) 117 { 118 errno = saved_errno; 119 return result; 120 } 121 } 122 else if (errno != EACCES) 123 return -1; 124 } 125# endif 126 127# if CHOWN_TRAILING_SLASH_BUG 128 if (!stat_valid) 129 { 130 size_t len = strlen (file); 131 if (len && file[len - 1] == '/' && stat (file, &st)) 132 return -1; 133 } 134# endif 135 136 result = chown (file, uid, gid); 137 138# if CHOWN_CHANGE_TIME_BUG 139 if (result == 0 && stat_valid 140 && (uid == st.st_uid || uid == (uid_t) -1) 141 && (gid == st.st_gid || gid == (gid_t) -1)) 142 { 143 /* No change in ownership, but at least one argument was not -1, 144 so we are required to update ctime. Since chown succeeded, 145 we assume that chmod will do likewise. Fortunately, on all 146 known systems where a 'no-op' chown skips the ctime update, a 147 'no-op' chmod still does the trick. */ 148 result = chmod (file, st.st_mode & (S_IRWXU | S_IRWXG | S_IRWXO 149 | S_ISUID | S_ISGID | S_ISVTX)); 150 } 151# endif 152 153 return result; 154} 155 156#endif /* HAVE_CHOWN */ 157