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 9a5c931439bd..742893ea7390 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;