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Date: Tue, 22 Jul 2014 14:00:03 -0700 (PDT)
From: Raphael Geissert <geissert@...ian.org>
To: Open Source Security <oss-security@...ts.openwall.com>
Subject: ecryptfs-setup-private nitpick
Hi,
Taking a look at ecryptfs-utils 103's ecryptfs-setup-private, there is a bit
of code that writes the mount pass to a file in /dev/shm hoping to "keep it
from leaking to the hard-drive":
8<-------->8
# This will be wrapped by pam_ecryptfs's chauthtok as soon as the
user
# chooses a password. Until that happens (hopefully soon), standard
# file permissions (600) are all that's protecting it. Write it to
# ramdisk, to keep it from leaking to the hard-drive.
temp=`mktemp /dev/shm/.ecryptfs-XXXXXX`
printf "%s" "$MOUNTPASS" > "$temp"
mv -f -T "$temp" "/dev/shm/.ecryptfs-$USER" || error "Could not
create passphrase file"
8<-------->8
Fastforward to 2014 and /dev/shm is, well, not a ramfs/ramdisk:
/dev/shm -> /run/shm, which is a tmpfs at least on Debian.
And as clearly stated by Documentation/filesystems/tmpfs.txt:
"If you compare it to ramfs (which was the template to create tmpfs)
you gain swapping and limit checking."
So in the hope of avoiding a persistent storage the mount pass is written to
a file in a tmpfs that can be swapped to... disk.
The file is left on /dev/shm until pam_ecryptfs actually wraps it with the
login pass.
Cheers,
--
Raphael Geissert - Debian Developer
www.debian.org - get.debian.net
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