larry@utecfa.UUCP (Larry Philps) (07/02/85)
Subject: chown(1) / chgrp(1) do not work on symbolic links
Index: /usr/src/bin/chgrp.c /usr/src/etc/chown.c 4.2BSD
Description:
The chown system call does not follow symbolic links in
namei so that it is possible to change the owner and group
of the link itself and not just what it points to. Also
chown(2) changes both the owner and group. Thus chown (1)
stat's the destination file in order to find its current group.
This value is then used in the call to chown (2). A similar
situtation exists for chgrp in which it needs to know the current
owner of the file before calling chown (2). However, both
chgrp and chown use the stat (2) system call, so that if you
try to chown/chgrp a symbolic link, the group/owner will end up
being set to the group/owner of the file the link points to.
Repeat-By:
Script started on Tue Jul 2 13:35:55 1985
# echo > junk
# chown 9998 junk
# chgrp 9999 junk
# ln -s junk symlink
# ls -lg symlink junk
-rw-r--r-- 1 9998 9999 0 Jul 2 13:36 junk
lrwxr-xr-x 1 0 0 4 Jul 2 13:36 symlink@ -> junk
# chown root symlink
# ls -lg junk symlink
-rw-r--r-- 1 9998 9999 0 Jul 2 13:36 junk
lrwxr-xr-x 1 0 9999 4 Jul 2 13:36 symlink@ -> junk
----
# rm symlink
# ln -s junk symlink
# ls -lg symlink junk
-rw-r--r-- 1 9998 9999 0 Jul 2 13:36 junk
lrwxr-xr-x 1 0 0 4 Jul 2 13:36 symlink@ -> junk
# chgrp daemon symlink
# lg -lg junk symlink
-rw-r--r-- 1 9998 9999 0 Jul 2 13:36 junk
lrwxr-xr-x 1 9998 1 4 Jul 2 13:37 symlink@ -> junk
----
Fix:
Change the call to stat (2) in both chgrp.c and chown.c to be
a call to lstat (2).
*** /tmp/,RCSt1001285 Tue Jul 2 13:43:07 1985
--- chown.c Tue Jul 2 11:29:46 1985
***************
*** 41,45
cho:
for(c=2; c<argc; c++) {
! stat(argv[c], &stbuf);
if(chown(argv[c], uid, stbuf.st_gid) < 0 && !fflag) {
perror(argv[c]);
--- 45,49 -----
cho:
for(c=2; c<argc; c++) {
! lstat(argv[c], &stbuf);
if(chown(argv[c], uid, stbuf.st_gid) < 0 && !fflag) {
perror(argv[c]);
*** /tmp/,RCSt1001291 Tue Jul 2 13:43:23 1985
--- chgrp.c Tue Jul 2 11:32:33 1985
***************
*** 71,75
ok:
for (c = 1; c < argc; c++) {
! if (stat(argv[c], &stbuf)) {
perror(argv[c]);
continue;
--- 72,76 -----
ok:
for (c = 1; c < argc; c++) {
! if (lstat(argv[c], &stbuf)) {
perror(argv[c]);
continue;
--
Larry Philps
Engineering Computing Facility
University of Toronto
{linus,ihnp4,uw-beaver,floyd,decvax,utzoo}!utcsri!utecfa!larry