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, 2005, 2006, 2007 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 2, or (at your option) 9 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, write to the Free Software Foundation, 18 Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. */ 19 20/* written by Jim Meyering */ 21 22#include <config.h> 23 24/* Specification. */ 25#include <unistd.h> 26 27#include <stdbool.h> 28#include <sys/types.h> 29#include <sys/stat.h> 30#include <fcntl.h> 31#include <errno.h> 32 33/* Below we refer to the system's chown(). */ 34#undef chown 35 36/* The results of open() in this file are not used with fchdir, 37 therefore save some unnecessary work in fchdir.c. */ 38#undef open 39#undef close 40 41/* Provide a more-closely POSIX-conforming version of chown on 42 systems with one or both of the following problems: 43 - chown doesn't treat an ID of -1 as meaning 44 `don't change the corresponding ID'. 45 - chown doesn't dereference symlinks. */ 46 47int 48rpl_chown (const char *file, uid_t uid, gid_t gid) 49{ 50#if CHOWN_FAILS_TO_HONOR_ID_OF_NEGATIVE_ONE 51 if (gid == (gid_t) -1 || uid == (uid_t) -1) 52 { 53 struct stat file_stats; 54 55 /* Stat file to get id(s) that should remain unchanged. */ 56 if (stat (file, &file_stats)) 57 return -1; 58 59 if (gid == (gid_t) -1) 60 gid = file_stats.st_gid; 61 62 if (uid == (uid_t) -1) 63 uid = file_stats.st_uid; 64 } 65#endif 66 67#if CHOWN_MODIFIES_SYMLINK 68 { 69 /* Handle the case in which the system-supplied chown function 70 does *not* follow symlinks. Instead, it changes permissions 71 on the symlink itself. To work around that, we open the 72 file (but this can fail due to lack of read or write permission) and 73 use fchown on the resulting descriptor. */ 74 int open_flags = O_NONBLOCK | O_NOCTTY; 75 int fd = open (file, O_RDONLY | open_flags); 76 if (0 <= fd 77 || (errno == EACCES 78 && 0 <= (fd = open (file, O_WRONLY | open_flags)))) 79 { 80 int result = fchown (fd, uid, gid); 81 int saved_errno = errno; 82 83 /* POSIX says fchown can fail with errno == EINVAL on sockets, 84 so fall back on chown in that case. */ 85 struct stat sb; 86 bool fchown_socket_failure = 87 (result != 0 && saved_errno == EINVAL 88 && fstat (fd, &sb) == 0 && S_ISFIFO (sb.st_mode)); 89 90 close (fd); 91 92 if (! fchown_socket_failure) 93 { 94 errno = saved_errno; 95 return result; 96 } 97 } 98 else if (errno != EACCES) 99 return -1; 100 } 101#endif 102 103 return chown (file, uid, gid); 104} 105