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, 29 insertions, 24 deletions

diff --git a/fs/ecryptfs/mmap.c b/fs/ecryptfs/mmap.c
index 55cec98a84e7..6df410c77264 100644
--- a/fs/ecryptfs/mmap.c
+++ b/fs/ecryptfs/mmap.c
@@ -56,9 +56,6 @@ static struct page *ecryptfs_get1page(struct file *file, int index)
         return read_mapping_page(mapping, index, (void *)file);
 }
 
-static
-int write_zeros(struct file *file, pgoff_t index, int start, int num_zeros);
-
 /**
  * ecryptfs_fill_zeros
  * @file: The ecryptfs file
@@ -101,10 +98,13 @@ int ecryptfs_fill_zeros(struct file *file, loff_t new_length)
         if (old_end_page_index == new_end_page_index) {
                 /* Start and end are in the same page; we just need to
                  * set a portion of the existing page to zero's */
-                rc = write_zeros(file, index, (old_end_pos_in_page + 1),
-                                 (new_end_pos_in_page - old_end_pos_in_page));
+                rc = ecryptfs_write_zeros(file, index,
+                                          (old_end_pos_in_page + 1),
+                                          (new_end_pos_in_page
+                                           - old_end_pos_in_page));
                 if (rc)
-                        ecryptfs_printk(KERN_ERR, "write_zeros(file=[%p], "
+                        ecryptfs_printk(KERN_ERR, "ecryptfs_write_zeros("
+                                        "file=[%p], "
                                         "index=[0x%.16x], "
                                         "old_end_pos_in_page=[d], "
                                         "(PAGE_CACHE_SIZE - new_end_pos_in_page"
@@ -117,10 +117,10 @@ int ecryptfs_fill_zeros(struct file *file, loff_t new_length)
                 goto out;
         }
         /* Fill the remainder of the previous last page with zeros */
-        rc = write_zeros(file, index, (old_end_pos_in_page + 1),
+        rc = ecryptfs_write_zeros(file, index, (old_end_pos_in_page + 1),
                          ((PAGE_CACHE_SIZE - 1) - old_end_pos_in_page));
         if (rc) {
-                ecryptfs_printk(KERN_ERR, "write_zeros(file=[%p], "
+                ecryptfs_printk(KERN_ERR, "ecryptfs_write_zeros(file=[%p], "
                                 "index=[0x%.16x], old_end_pos_in_page=[d], "
                                 "(PAGE_CACHE_SIZE - old_end_pos_in_page)=[d]) "
                                 "returned [%d]\n", file, index,
@@ -131,9 +131,10 @@ int ecryptfs_fill_zeros(struct file *file, loff_t new_length)
         index++;
         while (index < new_end_page_index) {
                 /* Fill all intermediate pages with zeros */
-                rc = write_zeros(file, index, 0, PAGE_CACHE_SIZE);
+                rc = ecryptfs_write_zeros(file, index, 0, PAGE_CACHE_SIZE);
                 if (rc) {
-                        ecryptfs_printk(KERN_ERR, "write_zeros(file=[%p], "
+                        ecryptfs_printk(KERN_ERR, "ecryptfs_write_zeros("
+                                        "file=[%p], "
                                         "index=[0x%.16x], "
                                         "old_end_pos_in_page=[d], "
                                         "(PAGE_CACHE_SIZE - new_end_pos_in_page"
@@ -149,9 +150,9 @@ int ecryptfs_fill_zeros(struct file *file, loff_t new_length)
         }
         /* Fill the portion at the beginning of the last new page with
          * zero's */
-        rc = write_zeros(file, index, 0, (new_end_pos_in_page + 1));
+        rc = ecryptfs_write_zeros(file, index, 0, (new_end_pos_in_page + 1));
         if (rc) {
-                ecryptfs_printk(KERN_ERR, "write_zeros(file="
+                ecryptfs_printk(KERN_ERR, "ecryptfs_write_zeros(file="
                                 "[%p], index=[0x%.16x], 0, "
                                 "new_end_pos_in_page=[%d]"
                                 "returned [%d]\n", file, index,
@@ -400,7 +401,6 @@ out:
 static int ecryptfs_prepare_write(struct file *file, struct page *page,
                                   unsigned from, unsigned to)
 {
-        loff_t pos;
         int rc = 0;
 
         if (from == 0 && to == PAGE_CACHE_SIZE)
@@ -408,14 +408,19 @@ static int ecryptfs_prepare_write(struct file *file, struct page *page,
                                    up to date. */
         if (!PageUptodate(page))
                 rc = ecryptfs_do_readpage(file, page, page->index);
-        pos = ((loff_t)page->index << PAGE_CACHE_SHIFT) + to;
-        if (pos > i_size_read(page->mapping->host)) {
-                rc = ecryptfs_truncate(file->f_path.dentry, pos);
-                if (rc) {
-                        printk(KERN_ERR "Error on attempt to "
-                               "truncate to (higher) offset [%lld];"
-                               " rc = [%d]\n", pos, rc);
-                        goto out;
+        if (page->index != 0) {
+                loff_t end_of_prev_pg_pos =
+                        (((loff_t)page->index << PAGE_CACHE_SHIFT) - 1);
+
+                if (end_of_prev_pg_pos > i_size_read(page->mapping->host)) {
+                        rc = ecryptfs_truncate(file->f_path.dentry,
+                                               end_of_prev_pg_pos);
+                        if (rc) {
+                                printk(KERN_ERR "Error on attempt to "
+                                       "truncate to (higher) offset [%lld];"
+                                       " rc = [%d]\n", end_of_prev_pg_pos, rc);
+                                goto out;
+                        }
                 }
         }
 out:
@@ -753,7 +758,7 @@ out:
 }
 
 /**
- * write_zeros
+ * ecryptfs_write_zeros
  * @file: The ecryptfs file
  * @index: The index in which we are writing
  * @start: The position after the last block of data
@@ -763,8 +768,8 @@ out:
  *
  * (start + num_zeros) must be less than or equal to PAGE_CACHE_SIZE
  */
-static
-int write_zeros(struct file *file, pgoff_t index, int start, int num_zeros)
+int
+ecryptfs_write_zeros(struct file *file, pgoff_t index, int start, int num_zeros)
 {
         int rc = 0;
         struct page *tmp_page;