after more thought regarding xattrs, i looked at the sementecs
regarding users changing traditional attributes on world writable
files they don't own, in this case mtime and noticed a bug in XFS.
on ext2 filesystems if i attempt to set the mtime of a file i don't
own (but do have write permission to) to anything but the current time
i get -EPERM, but on XFS im allowed to do whatever i want:
eb@dogbert ~$ mount | grep -w /
/dev/hda3 on / type xfs (rw)
eb@dogbert ~$ mount | grep /mnt
/dev/hda4 on /mnt type ext2 (rw)
eb@dogbert ~$ ls -l /dev/null /mnt/null
crw-rw-rw- 1 root root 1, 3 Jun 28 2001 /dev/null
crw-rw-rw- 1 root root 1, 3 Apr 5 23:47 /mnt/null
eb@dogbert ~$ touch -r /etc/passwd /mnt/null
touch: setting times of `/mnt/null': Operation not permitted
eb@dogbert ~$ touch -r /etc/passwd /dev/null
eb@dogbert ~$ ls -l /etc/passwd /dev/null
crw-rw-rw- 1 root root 1, 3 Feb 16 06:00 /dev/null
-rw-r--r-- 1 root root 1408 Feb 16 06:00 /etc/passwd
eb@dogbert ~$ ls -l /dev/null /mnt/null
crw-rw-rw- 1 root root 1, 3 Feb 16 06:00 /dev/null
crw-rw-rw- 1 root root 1, 3 Apr 5 23:47 /mnt/null
eb@dogbert ~$
the same is true for setting time in the future, also the same applies
to normal files as opposed to regular files.