ocfs2: Zero the tail cluster when extending past i_size.

ocfs2's allocation unit is the cluster.  This can be larger than a block
or even a memory page.  This means that a file may have many blocks in
its last extent that are beyond the block containing i_size.  There also
may be more unwritten extents after that.

When ocfs2 grows a file, it zeros the entire cluster in order to ensure
future i_size growth will see cleared blocks.  Unfortunately,
block_write_full_page() drops the pages past i_size.  This means that
ocfs2 is actually leaking garbage data into the tail end of that last
cluster.  This is a bug.

We adjust ocfs2_write_begin_nolock() and ocfs2_extend_file() to detect
when a write or truncate is past i_size.  They will use
ocfs2_zero_extend() to ensure the data is properly zeroed.

Older versions of ocfs2_zero_extend() simply zeroed every block between
i_size and the zeroing position.  This presumes three things:

1) There is allocation for all of these blocks.
2) The extents are not unwritten.
3) The extents are not refcounted.

(1) and (2) hold true for non-sparse filesystems, which used to be the
only users of ocfs2_zero_extend().  (3) is another bug.

Since we're now using ocfs2_zero_extend() for sparse filesystems as
well, we teach ocfs2_zero_extend() to check every extent between
i_size and the zeroing position.  If the extent is unwritten, it is
ignored.  If it is refcounted, it is CoWed.  Then it is zeroed.

Signed-off-by: Joel Becker <joel.becker@oracle.com>
Cc: stable@kernel.org

1 files changed, 28 insertions, 14 deletions

diff --git a/fs/ocfs2/aops.c b/fs/ocfs2/aops.c
index 9a5c931439b..742893ea739 100644
--- a/fs/ocfs2/aops.c
+++ b/fs/ocfs2/aops.c
@@ -196,15 +196,14 @@ int ocfs2_get_block(struct inode *inode, sector_t iblock,
 			dump_stack();
 			goto bail;
 		}
-
-		past_eof = ocfs2_blocks_for_bytes(inode->i_sb, i_size_read(inode));
-		mlog(0, "Inode %lu, past_eof = %llu\n", inode->i_ino,
-		     (unsigned long long)past_eof);
-
-		if (create && (iblock >= past_eof))
-			set_buffer_new(bh_result);
 	}
 
+	past_eof = ocfs2_blocks_for_bytes(inode->i_sb, i_size_read(inode));
+	mlog(0, "Inode %lu, past_eof = %llu\n", inode->i_ino,
+	     (unsigned long long)past_eof);
+	if (create && (iblock >= past_eof))
+		set_buffer_new(bh_result);
+
 bail:
 	if (err < 0)
 		err = -EIO;
@@ -1590,21 +1589,20 @@ out:
  * write path can treat it as an non-allocating write, which has no
  * special case code for sparse/nonsparse files.
  */
-static int ocfs2_expand_nonsparse_inode(struct inode *inode, loff_t pos,
-					unsigned len,
+static int ocfs2_expand_nonsparse_inode(struct inode *inode,
+					struct buffer_head *di_bh,
+					loff_t pos, unsigned len,
 					struct ocfs2_write_ctxt *wc)
 {
 	int ret;
-	struct ocfs2_super *osb = OCFS2_SB(inode->i_sb);
 	loff_t newsize = pos + len;
 
-	if (ocfs2_sparse_alloc(osb))
-		return 0;
+	BUG_ON(ocfs2_sparse_alloc(OCFS2_SB(inode->i_sb)));
 
 	if (newsize <= i_size_read(inode))
 		return 0;
 
-	ret = ocfs2_extend_no_holes(inode, newsize, pos);
+	ret = ocfs2_extend_no_holes(inode, di_bh, newsize, pos);
 	if (ret)
 		mlog_errno(ret);
 
@@ -1614,6 +1612,18 @@ static int ocfs2_expand_nonsparse_inode(struct inode *inode, loff_t pos,
 	return ret;
 }
 
+static int ocfs2_zero_tail(struct inode *inode, struct buffer_head *di_bh,
+			   loff_t pos)
+{
+	int ret = 0;
+
+	BUG_ON(!ocfs2_sparse_alloc(OCFS2_SB(inode->i_sb)));
+	if (pos > i_size_read(inode))
+		ret = ocfs2_zero_extend(inode, di_bh, pos);
+
+	return ret;
+}
+
 int ocfs2_write_begin_nolock(struct address_space *mapping,
 			     loff_t pos, unsigned len, unsigned flags,
 			     struct page **pagep, void **fsdata,
@@ -1649,7 +1659,11 @@ int ocfs2_write_begin_nolock(struct address_space *mapping,
 		}
 	}
 
-	ret = ocfs2_expand_nonsparse_inode(inode, pos, len, wc);
+	if (ocfs2_sparse_alloc(osb))
+		ret = ocfs2_zero_tail(inode, di_bh, pos);
+	else
+		ret = ocfs2_expand_nonsparse_inode(inode, di_bh, pos, len,
+						   wc);
 	if (ret) {
 		mlog_errno(ret);
 		goto out;