eCryptfs: Use entire helper page during page crypto operations

When encrypting eCryptfs pages and decrypting pages from the lower
filesystem, utilize the entire helper page rather than only the first
4096 bytes.

This only affects architectures where PAGE_CACHE_SIZE is larger than
4096 bytes.
Signed-off-by: Tyler Hicks <tyhicks@canonical.com>

fs/ecryptfs/crypto.c

@@ -450,9 +450,10 @@ static int ecryptfs_encrypt_extent(struct page *enc_extent_page,
 			(unsigned long long)(extent_base + extent_offset), rc);
 		goto out;
 	}
-	rc = ecryptfs_encrypt_page_offset(crypt_stat, enc_extent_page, 0,
-					  page, (extent_offset
-						 * crypt_stat->extent_size),
+	rc = ecryptfs_encrypt_page_offset(crypt_stat, enc_extent_page,
+					extent_offset * crypt_stat->extent_size,
+					page,
+					extent_offset * crypt_stat->extent_size,
 					crypt_stat->extent_size, extent_iv);
 	if (rc < 0) {
 		printk(KERN_ERR "%s: Error attempting to encrypt page with "
@@ -520,7 +521,8 @@ int ecryptfs_encrypt_page(struct page *page)
 				   * (PAGE_CACHE_SIZE
 				      / crypt_stat->extent_size))
 				  + extent_offset), crypt_stat);
-		rc = ecryptfs_write_lower(ecryptfs_inode, enc_extent_virt,
+		rc = ecryptfs_write_lower(ecryptfs_inode, (enc_extent_virt +
+				extent_offset * crypt_stat->extent_size),
 				offset, crypt_stat->extent_size);
 		if (rc < 0) {
 			ecryptfs_printk(KERN_ERR, "Error attempting "
@@ -558,9 +560,9 @@ static int ecryptfs_decrypt_extent(struct page *page,
 		goto out;
 	}
 	rc = ecryptfs_decrypt_page_offset(crypt_stat, page,
-					  (extent_offset
-					   * crypt_stat->extent_size),
-					  enc_extent_page, 0,
+					extent_offset * crypt_stat->extent_size,
+					enc_extent_page,
+					extent_offset * crypt_stat->extent_size,
 					crypt_stat->extent_size, extent_iv);
 	if (rc < 0) {
 		printk(KERN_ERR "%s: Error attempting to decrypt to page with "
@@ -620,8 +622,9 @@ int ecryptfs_decrypt_page(struct page *page)
 			&offset, ((page->index * (PAGE_CACHE_SIZE
 						  / crypt_stat->extent_size))
 				  + extent_offset), crypt_stat);
-		rc = ecryptfs_read_lower(enc_extent_virt, offset,
-					 crypt_stat->extent_size,
+		rc = ecryptfs_read_lower((enc_extent_virt +
+				extent_offset * crypt_stat->extent_size),
+				offset, crypt_stat->extent_size,
 				ecryptfs_inode);
 		if (rc < 0) {
 			ecryptfs_printk(KERN_ERR, "Error attempting "