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mtime permission

To: linux-xfs@xxxxxxxxxxx
Subject: mtime permission
From: Ethan Benson <erbenson@xxxxxxxxxx>
Date: Fri, 5 Apr 2002 23:58:29 -0900
Sender: owner-linux-xfs@xxxxxxxxxxx
User-agent: Mutt/1.2.5i
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.

-- 
Ethan Benson
http://www.alaska.net/~erbenson/

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