Patch "ext4: fix data exposure after a crash" has been added to the 4.6-stable tree

This is a note to let you know that I've just added the patch titled

ext4: fix data exposure after a crash

to the 4.6-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
ext4-fix-data-exposure-after-a-crash.patch
and it can be found in the queue-4.6 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Jan Kara <[email protected]>
Date: Sun, 24 Apr 2016 00:56:03 -0400
Subject: ext4: fix data exposure after a crash

From: Jan Kara <[email protected]>

commit 06bd3c36a733ac27962fea7d6f47168841376824 upstream.

Huang has reported that in his powerfail testing he is seeing stale block contents in some of recently allocated blocks although he mounts ext4 in data=ordered mode. After some investigation I have found out that indeed when delayed allocation is used, we don't add inode to transaction's list of inodes needing flushing before commit. Originally we were doing that but commit f3b59291a69d removed the logic with a flawed argument that it is not needed.

The problem is that although for delayed allocated blocks we write their contents immediately after allocating them, there is no guarantee that the IO scheduler or device doesn't reorder things and thus transaction allocating blocks and attaching them to inode can reach stable storage before actual block contents. Actually whenever we attach freshly allocated blocks to inode using a written extent, we should add inode to transaction's ordered inode list to make sure we properly wait for block contents to be written before committing the transaction. So that is what we do in this patch. This also handles other cases where stale data exposure was possible - like filling hole via mmap in data=ordered,nodelalloc mode.

The only exception to the above rule are extending direct IO writes where blkdev_direct_IO() waits for IO to complete before increasing i_size and thus stale data exposure is not possible. For now we don't complicate the code with optimizing this special case since the overhead is pretty low. In case this is observed to be a performance problem we can always handle it using a special flag to ext4_map_blocks().

---
 fs/ext4/inode.c |   24 +++++++++++++++---------
 1 file changed, 15 insertions(+), 9 deletions(-)

@@ -684,6 +684,21 @@ out_sem:
 		ret = check_block_validity(inode, map);
 		if (ret != 0)
 			return ret;
+
+		/*
+		 * Inodes with freshly allocated blocks where contents will be
+		 * visible after transaction commit must be on transaction's
+		 * ordered data list.
+		 */
+		if (map->m_flags & EXT4_MAP_NEW &&
+		    !(map->m_flags & EXT4_MAP_UNWRITTEN) &&
+		    !(flags & EXT4_GET_BLOCKS_ZERO) &&
+		    !IS_NOQUOTA(inode) &&
+		    ext4_should_order_data(inode)) {
+			ret = ext4_jbd2_file_inode(handle, inode);
+			if (ret)
+				return ret;
+		}
 	}
 	return retval;
 }

@@ -1289,15 +1304,6 @@ static int ext4_write_end(struct file *f
 	int i_size_changed = 0;
 
 	trace_ext4_write_end(inode, pos, len, copied);
-	if (ext4_test_inode_state(inode, EXT4_STATE_ORDERED_MODE)) {
-		ret = ext4_jbd2_file_inode(handle, inode);
-		if (ret) {
-			unlock_page(page);
-			put_page(page);
-			goto errout;
-		}
-	}
-
 	if (ext4_has_inline_data(inode)) {
 		ret = ext4_write_inline_data_end(inode, pos, len,
 						 copied, page);

Patches currently in stable-queue which might be from [email protected] are

queue-4.6/ext4-fix-check-of-dqget-return-value-in-ext4_ioctl_setproject.patch queue-4.6/ext4-fix-data-exposure-after-a-crash.patch queue-4.6/ext4-fix-oops-on-corrupted-filesystem.patch