ecryptfs: fix fsx data corruption problems

ecryptfs in 2.6.24-rc3 wasn't surviving fsx for me at all, dying after 4
ops.  Generally, encountering problems with stale data and improperly
zeroed pages.  An extending truncate + write for example would expose stale
data.

With the changes below I got to a million ops and beyond with all mmap ops
disabled - mmap still needs work.  (A version of this patch on a RHEL5
kernel ran for over 110 million fsx ops)

I added a few comments as well, to the best of my understanding
as I read through the code.

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Acked-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>

2 files changed, 41 insertions, 17 deletions

diff --git a/fs/ecryptfs/mmap.c b/fs/ecryptfs/mmap.c
index 16a7a555f392..32c5711d79a3 100644
--- a/fs/ecryptfs/mmap.c
+++ b/fs/ecryptfs/mmap.c
@@ -263,14 +263,13 @@ out:
         return 0;
 }
 
+/* This function must zero any hole we create */
 static int ecryptfs_prepare_write(struct file *file, struct page *page,
                                   unsigned from, unsigned to)
 {
         int rc = 0;
+        loff_t prev_page_end_size;
 
-        if (from == 0 && to == PAGE_CACHE_SIZE)
-                goto out;       /* If we are writing a full page, it will be
-                                   up to date. */
         if (!PageUptodate(page)) {
                 rc = ecryptfs_read_lower_page_segment(page, page->index, 0,
                                                       PAGE_CACHE_SIZE,
@@ -283,22 +282,32 @@ static int ecryptfs_prepare_write(struct file *file, struct page *page,
                 } else
                         SetPageUptodate(page);
         }
-        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)) {
+        prev_page_end_size = ((loff_t)page->index << PAGE_CACHE_SHIFT);
+
+        /*
+         * If creating a page or more of holes, zero them out via truncate.
+         * Note, this will increase i_size.
+         */
+        if (page->index != 0) {
+                if (prev_page_end_size > i_size_read(page->mapping->host)) {
                         rc = ecryptfs_truncate(file->f_path.dentry,
-                                               end_of_prev_pg_pos);
+                                               prev_page_end_size);
                         if (rc) {
                                 printk(KERN_ERR "Error on attempt to "
                                        "truncate to (higher) offset [%lld];"
-                                       " rc = [%d]\n", end_of_prev_pg_pos, rc);
+                                       " rc = [%d]\n", prev_page_end_size, rc);
                                 goto out;
                         }
                 }
-                if (end_of_prev_pg_pos + 1 > i_size_read(page->mapping->host))
-                        zero_user_page(page, 0, PAGE_CACHE_SIZE, KM_USER0);
+        }
+        /*
+         * Writing to a new page, and creating a small hole from start of page?
+         * Zero it out.
+         */
+        if ((i_size_read(page->mapping->host) == prev_page_end_size) &&
+            (from != 0)) {
+                zero_user_page(page, 0, PAGE_CACHE_SIZE, KM_USER0);
         }
 out:
         return rc;
diff --git a/fs/ecryptfs/read_write.c b/fs/ecryptfs/read_write.c
index 6b7474a4336a..948f57624c05 100644
--- a/fs/ecryptfs/read_write.c
+++ b/fs/ecryptfs/read_write.c
@@ -124,6 +124,10 @@ int ecryptfs_write(struct file *ecryptfs_file, char *data, loff_t offset,
         loff_t pos;
         int rc = 0;
 
+        /*
+         * if we are writing beyond current size, then start pos
+         * at the current size - we'll fill in zeros from there.
+         */
         if (offset > ecryptfs_file_size)
                 pos = ecryptfs_file_size;
         else
@@ -137,6 +141,7 @@ int ecryptfs_write(struct file *ecryptfs_file, char *data, loff_t offset,
                 if (num_bytes > total_remaining_bytes)
                         num_bytes = total_remaining_bytes;
                 if (pos < offset) {
+                        /* remaining zeros to write, up to destination offset */
                         size_t total_remaining_zeros = (offset - pos);
 
                         if (num_bytes > total_remaining_zeros)
@@ -167,17 +172,27 @@ int ecryptfs_write(struct file *ecryptfs_file, char *data, loff_t offset,
                         }
                 }
                 ecryptfs_page_virt = kmap_atomic(ecryptfs_page, KM_USER0);
+
+                /*
+                 * pos: where we're now writing, offset: where the request was
+                 * If current pos is before request, we are filling zeros
+                 * If we are at or beyond request, we are writing the *data*
+                 * If we're in a fresh page beyond eof, zero it in either case
+                 */
+                if (pos < offset || !start_offset_in_page) {
+                        /* We are extending past the previous end of the file.
+                         * Fill in zero values to the end of the page */
+                        memset(((char *)ecryptfs_page_virt
+                                + start_offset_in_page), 0,
+                                PAGE_CACHE_SIZE - start_offset_in_page);
+                }
+
+                /* pos >= offset, we are now writing the data request */
                 if (pos >= offset) {
                         memcpy(((char *)ecryptfs_page_virt
                                 + start_offset_in_page),
                                (data + data_offset), num_bytes);
                         data_offset += num_bytes;
-                } else {
-                        /* We are extending past the previous end of the file.
-                         * Fill in zero values up to the start of where we
-                         * will be writing data. */
-                        memset(((char *)ecryptfs_page_virt
-                                + start_offset_in_page), 0, num_bytes);
                 }
                 kunmap_atomic(ecryptfs_page_virt, KM_USER0);
                 flush_dcache_page(ecryptfs_page);