[Lucid][SRU][PATCH 0/1] eCryptfs: Use notify_change for truncating lower inodes

[Colin King]

From: Colin Ian King <colin.king at canonical.com>

SRU Justification:

When truncating inodes in the lower filesystem, eCryptfs directly
invoked vmtruncate(). As Christoph Hellwig pointed out, vmtruncate() is
a filesystem helper function, but filesystems may need to do more than
just a call to vmtruncate().  eCryptfs needs to go through 
notify_change()->setattr to ensure truncate works reliable without
corruption or leaking blocks on a variety of filesystems.

See: http://thread.gmane.org/gmane.linux.file-systems/36105

Fix: With this patch , lower inode truncation is moved out of
ecryptfs_truncate() and the function is renamed to truncate_upper().
truncate_upper() updates an iattr for the lower inode to indicate
if the lower inode needs to be truncated upon return.
ecryptfs_setattr() then calls notify_change(), using the updated iattr
for the lower inode, to complete the truncation.

Without the patch we risk corrupting or leaking blocks on the lower
filesystem.

Has been soak tested with a variety of ftruncate() soak tests and also
running a full kernel build on ecryptfs with a lower ext4 filesystem.

https://bugs.launchpad.net/bugs/451368

This is a backport of commit 5f3ef64f4da1c587cdcfaaac72311225b7df094c

Colin Ian King (1):
  eCryptfs: Use notify_change for truncating lower inodes

 fs/ecryptfs/inode.c |   99 ++++++++++++++++++++++++++++++++++----------------
 1 files changed, 67 insertions(+), 32 deletions(-)