ecryptfs team mailing list archive

[Dustin Kirkland <dustin.kirkland@xxxxxxxxx>]

Okay, on the userspace side, we need to provide a way to "fix" affected
files, where kernel data has been leaked into the encrypted file
headers, once the user is running a fixed kernel.

I have created a small shell script, ecryptfs-rewrite-file, which will
do this, and a manpage with instructions.

You can view the latest source of this shell script in the source control at:
 * http://bazaar.launchpad.net/~ecryptfs/ecryptfs/ecryptfs-utils/annotate/head%3A/src/utils//ecryptfs-rewrite-file

And this manpage explains how the script is intended to run:
 * http://bazaar.launchpad.net/~ecryptfs/ecryptfs/ecryptfs-utils/annotate/head%3A/doc/manpage//ecryptfs-rewrite-file.1

Basically:
 $ cd $YOUR_MOUNT_POINT
 $ find . -xdev -print0 | xargs -r -0 /usr/bin/ecryptfs-rewrite-file
 $ ecryptfs-umount-private
 $ sync

This will mostly affect Ubuntu Jaunty Alpha/Beta users.  I will
coordinate with the Ubuntu Security Team for the best mechanism for
communicating these instructions.

This script will be in the ecryptfs-utils-73 release for merging by
other distros too.

:-Dustin

** Changed in: ecryptfs-utils (Ubuntu)
       Status: Confirmed => In Progress

** Also affects: linux (Ubuntu)
   Importance: Undecided
       Status: New

** Changed in: linux (Ubuntu)
   Importance: Undecided => Critical
     Assignee: (unassigned) => Tim Gardner (timg-tpi)
       Status: New => In Progress
       Target: None => ubuntu-9.04

-- 
ecryptfs stores ram contents in plaintext in the container as padding
https://bugs.launchpad.net/bugs/345544
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which is a direct subscriber.

Status in eCryptfs - Enterprise Cryptographic Filesystem: In Progress
Status in “ecryptfs-utils” source package in Ubuntu: In Progress
Status in “linux” source package in Ubuntu: In Progress
Status in ecryptfs-utils in Ubuntu Jaunty: In Progress
Status in linux in Ubuntu Jaunty: In Progress

Bug description:
Environment: 
Linux flst61nb 2.6.28-gentoo-r2 #4 SMP Tue Mar 17 12:38:43 CET 2009 x86_64 Intel(R) Core(TM)2 Duo CPU T8300 @ 2.40GHz GenuineIntel GNU/Linux

When looking at the contents of the encrypted files I see random content of my System RAM. 
Including the content of ~/.ssh/known_hosts, firefox Cache (html page headers) etc.

It seems ecryptfs fails in padding the files, it even seems that the padding is done after encryption.

To reproduce: 
# mkdir ecryptfs_base
# sudo mount -t ecryptfs ecryptfs_base ecryptfs_base
# cd ecryptfs_base/
# for ((i=0;i<10000;i++)); do dd if=/dev/zero of=$(date +"%s-$i") bs=1 count=1 >/dev/null 2>&1; done
# cd ..
# sudo umount ecryptfs_base/
# strings ecryptfs_base/*

Most of the files contain the String _CONSOLE, some contain just filenames, some the contents of random files.

An attacker with access to the underlying filesystem thus can find random data of the system using ecryptfs lying around in plain inside the files.

I also found the contents of /etc/mtab in some of the files...

/tmp/ecryptfs_base /tmp/ecryptfs_base ecryptfs rw,ecryptfs_sig=90fe7cccfdb1a0ba,ecryptfs_cipher=aes,ecryptfs_key_bytes=16 0 0

so one can find out which key was used to mount the fs

In addition I think there could also be private data of privileged processes run by root in some of the files, so an attacker could use ecryptfs to read (kernel?) memory and might find a password or similar.