eCryptfs: fix write zeros behavior

This patch fixes the processes involved in wiping regions of the data during
truncate and write events, fixing a kernel hang in 2.6.22-rc4 while assuring
that zero values are written out to the appropriate locations during events in
which the i_size will change.

The range passed to ecryptfs_truncate() from ecryptfs_prepare_write() includes
the page that is the object of ecryptfs_prepare_write().  This leads to a
kernel hang as read_cache_page() is executed on the same page in the
ecryptfs_truncate() execution path.  This patch remedies this by limiting the
range passed to ecryptfs_truncate() so as to exclude the page that is the
object of ecryptfs_prepare_write(); it also adds code to
ecryptfs_prepare_write() to zero out the region of its own page when writing
past the i_size position.  This patch also modifies ecryptfs_truncate() so
that when a file is truncated to a smaller size, eCryptfs will zero out the
contents of the new last page from the new size through to the end of the last
page.

Signed-off-by: Michael Halcrow <mhalcrow@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 2 insertions, 0 deletions

diff --git a/fs/ecryptfs/ecryptfs_kernel.h b/fs/ecryptfs/ecryptfs_kernel.h
index 403e3bad1455..1b9dd9a96f19 100644
--- a/fs/ecryptfs/ecryptfs_kernel.h
+++ b/fs/ecryptfs/ecryptfs_kernel.h
@@ -580,5 +580,7 @@ void
 ecryptfs_write_header_metadata(char *virt,
 			       struct ecryptfs_crypt_stat *crypt_stat,
 			       size_t *written);
+int ecryptfs_write_zeros(struct file *file, pgoff_t index, int start,
+			 int num_zeros);
 
 #endif /* #ifndef ECRYPTFS_KERNEL_H */