On 10/7/11 1:35 PM, Darrick J. Wong wrote:

On Fri, Oct 07, 2011 at 12:11:05AM -0700, Allison Henderson wrote:

quoted

This patch modifies both ext4 and jbd2 such that the journal
blocks which may contain file data, are securely deleted
after the files data blocks are deleted.

Because old journal blocks may contain file data, we need
a way to find those blocks again when it comes time to secure
delete the file.  This patch adds a new list to the journal
structure to keep track of which vfs blocks the journal blocks
contain.

After a truncate or a punch hole operation has completed, a
new function ext4_secure_delete_jblks is called that flushes
the journal, and then searches the list for any journal blocks
that were used to journal the blocks that were just removed.
The found journal blocks are then secure deleted.

And what about directory data?  Those would appear to remain in the
journal at least...  And xattrs?

#!/bin/bash

rm -f testsecdel
truncate --size 256m  testsecdel
mkfs.ext4 -F testsecdel &>/dev/null
mount -o loop testsecdel mnt/
echo securedata > mnt/securefilename
setfattr -n user.securexattrname -v securexattrvalue mnt/securefilename 
LONGATTR=`for I in 1 2 3 4 5 6 7 8 9 0; do echo -n veryveryveryveryveryveryverylongsecurexattrvalue; done`
setfattr -n user.longsecurexattrname -v $LONGATTR mnt/securefilename 
sync

rm -f mnt/securefilename
umount mnt
strings testsecdel 

yields:

/mnt/test2/mnt
lost+found
securexattrname
Ylongsecurexattrname
mselinux
veryveryveryveryveryveryverylongsecurexattrvalueveryveryveryveryveryveryverylongsecurexattrvalueveryveryveryveryveryveryverylongsecurexattrvalueveryveryveryveryveryveryverylongsecurexattrvalueveryveryveryveryveryveryverylongsecurexattrvalueveryveryveryveryveryveryverylongsecurexattrvalueveryveryveryveryveryveryverylongsecurexattrvalueveryveryveryveryveryveryverylongsecurexattrvalueveryveryveryveryveryveryverylongsecurexattrvalueveryveryveryveryveryveryverylongsecurexattrvaluesecurexattrvalueunconfined_u:object_r:file_t:s0
lost+found
securefilename
/mnt/test2/mnt

(this was with ext4.ko hacked to always enable secure delete)

-Eric