The patch protects from leaking sensitive data after resume from suspend.
During suspend a temporary key is created and this key is used to encrypt the
data written to disk.  When, during resume, the data was read back into memory
the temporary key is destroyed which simply means that all data written to
disk during suspend are then inaccessible so they can't be stolen lateron.

Think of the following: you suspend while an application is running that keeps
sensitive data in memory.  The application itself prevents the data from being
swapped out.  Suspend, however, must write these data to swap to be able to
resume lateron.  Without suspend encryption your sensitive data are then
stored in plaintext on disk.  This means that after resume your sensitive data
are accessible to all applications having direct access to the swap device
which was used for suspend.  If you don't need swap after resume these data
can remain on disk virtually forever.  Thus it can happen that your system
gets broken in weeks later and sensitive data which you thought were encrypted
and protected are retrieved and stolen from the swap device.
Signed-off-by: Andreas Steinmetz <ast@domdv.de>
Acked-by: Pavel Machek <pavel@suse.cz>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>