Date: Wed, 23 Jul 2014 22:37:08 +1000 From: Michael Samuel <mik@...net.net> To: oss-security@...ts.openwall.com Subject: Re: ecryptfs-setup-private nitpick Perhaps I'm wrong, but it appears that at-least on my system encrypted swap comes up very early in boot - maybe even before the urandom rcS.d script. Should urandom be an upstart script which any crypto daemons depend on (including cryptdisks-udev), rather than rcS.d? On 23 July 2014 17:23, Dustin Kirkland <kirkland@...ntu.com> wrote: > On Tue, Jul 22, 2014 at 3:35 PM, Tyler Hicks <tyhicks@...onical.com> wrote: >> Hi Raphael! >> >> On 2014-07-22 14:00:03, Raphael Geissert wrote: >>> 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. >> >> I consider encrypted swap to be a prerequisite to enabling any >> disk/file encryption solution. Ubuntu sets up encrypted swap when the >> user selects to encrypt their home directory from the installer. >> >> Unfortunately, the ecryptfs-setup-private man page doesn't recommend >> encrypting your swap but ecryptfs-utils ships a script called >> ecryptfs-setup-swap that enables encrypted swap. > > +1, always encrypt your swap, if you have any respect or concern for > the privacy of the data on your computer. We've tried to make it as > easy as possible to encrypt your swap in Ubuntu and ecryptfs. The > documentation could be updated to make this more clear. > >> Ignoring the encrypted swap argument, ecryptfs-setup-private shouldn't >> be storing the plaintext mount passphrase in a manner that is swappable. >> I think POSIX shared memory segments should provide the persistence and >> pinnable memory (SHM_LOCKED) needed. >> >> Either Dustin (cc'ed) or I will make this improvement. Thanks for the >> feedback! > > Indeed, thanks! > >> Tyler >> >>> >>> 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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