ecryptfs: remove unnecessary decrypt when extending a file

Removes an unecessary page decrypt from ecryptfs_begin_write when the
page is beyond the current file size. Previously, the call to
ecryptfs_decrypt_page would result in a read of 0 bytes, but still
attempt to decrypt an entire page. This patch detects that case and
merely zeros the page before marking it up-to-date.

Signed-off-by: Frank Swiderski <fes@chromium.org>
Signed-off-by: Tyler Hicks <tyhicks@linux.vnet.ibm.com>

1 files changed, 14 insertions, 8 deletions

diff --git a/fs/ecryptfs/mmap.c b/fs/ecryptfs/mmap.c
index 4b901139273..cc64fca89f8 100644
--- a/fs/ecryptfs/mmap.c
+++ b/fs/ecryptfs/mmap.c
@@ -290,6 +290,7 @@ static int ecryptfs_write_begin(struct file *file,
                 return -ENOMEM;
         *pagep = page;
 
+        prev_page_end_size = ((loff_t)index << PAGE_CACHE_SHIFT);
         if (!PageUptodate(page)) {
                 struct ecryptfs_crypt_stat *crypt_stat =
                         &ecryptfs_inode_to_private(mapping->host)->crypt_stat;
@@ -335,18 +336,23 @@ static int ecryptfs_write_begin(struct file *file,
                                 SetPageUptodate(page);
                         }
                 } else {
-                        rc = ecryptfs_decrypt_page(page);
-                        if (rc) {
-                                printk(KERN_ERR "%s: Error decrypting page "
-                                       "at index [%ld]; rc = [%d]\n",
-                                       __func__, page->index, rc);
-                                ClearPageUptodate(page);
-                                goto out;
+                        if (prev_page_end_size
+                            >= i_size_read(page->mapping->host)) {
+                                zero_user(page, 0, PAGE_CACHE_SIZE);
+                        } else {
+                                rc = ecryptfs_decrypt_page(page);
+                                if (rc) {
+                                        printk(KERN_ERR "%s: Error decrypting "
+                                               "page at index [%ld]; "
+                                               "rc = [%d]\n",
+                                               __func__, page->index, rc);
+                                        ClearPageUptodate(page);
+                                        goto out;
+                                }
                         }
                         SetPageUptodate(page);
                 }
         }
-        prev_page_end_size = ((loff_t)index << PAGE_CACHE_SHIFT);
         /* If creating a page or more of holes, zero them out via truncate.
          * Note, this will increase i_size. */
         if (index != 0) {