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>
diff --git a/fs/ecryptfs/read_write.c b/fs/ecryptfs/read_write.c
index 6b7474a..948f576 100644
--- a/fs/ecryptfs/read_write.c
+++ b/fs/ecryptfs/read_write.c
@@ -124,6 +124,10 @@
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 @@
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 @@
}
}
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);