[PATCH v3 3/3] xfs: correct the zeroing truncate range

[Zhang Yi]

From: Zhang Yi <yi.zhang@xxxxxxxxxx>

When truncating a realtime file unaligned to a shorter size,
xfs_setattr_size() only flush the EOF page before zeroing out, and
xfs_truncate_page() also only zeros the EOF block. This could expose
stale data since 943bc0882ceb ("iomap: don't increase i_size if it's not
a write operation").

If the sb_rextsize is bigger than one block, and we have a realtime
inode that contains a long enough written extent. If we unaligned
truncate into the middle of this extent, xfs_itruncate_extents() could
split the extent and align the it's tail to sb_rextsize, there maybe
have more than one blocks more between the end of the file. Since
xfs_truncate_page() only zeros the trailing portion of the i_blocksize()
value, so it may leftover some blocks contains stale data that could be
exposed if we append write it over a long enough distance later.

xfs_truncate_page() should flush, zeros out the entire rtextsize range,
and make sure the entire zeroed range have been flushed to disk before
updating the inode size.

Fixes: 943bc0882ceb ("iomap: don't increase i_size if it's not a write operation")
Reported-by: Chandan Babu R <chandanbabu@xxxxxxxxxx>
Link: https://lore.kernel.org/linux-xfs/0b92a215-9d9b-3788-4504-a520778953c2@xxxxxxxxxxxxxxx
Signed-off-by: Zhang Yi <yi.zhang@xxxxxxxxxx>
---
 fs/xfs/xfs_iomap.c | 35 +++++++++++++++++++++++++++++++----
 fs/xfs/xfs_iops.c  | 10 ----------
 2 files changed, 31 insertions(+), 14 deletions(-)

diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
index 4958cc3337bc..fc379450fe74 100644
--- a/fs/xfs/xfs_iomap.c
+++ b/fs/xfs/xfs_iomap.c
@@ -1466,12 +1466,39 @@ xfs_truncate_page(
 	loff_t			pos,
 	bool			*did_zero)
 {
+	struct xfs_mount	*mp = ip->i_mount;
 	struct inode		*inode = VFS_I(ip);
 	unsigned int		blocksize = i_blocksize(inode);
+	int			error;
+
+	if (XFS_IS_REALTIME_INODE(ip))
+		blocksize = XFS_FSB_TO_B(mp, mp->m_sb.sb_rextsize);
+
+	/*
+	 * iomap won't detect a dirty page over an unwritten block (or a
+	 * cow block over a hole) and subsequently skips zeroing the
+	 * newly post-EOF portion of the page. Flush the new EOF to
+	 * convert the block before the pagecache truncate.
+	 */
+	error = filemap_write_and_wait_range(inode->i_mapping, pos,
+					     roundup_64(pos, blocksize));
+	if (error)
+		return error;
 
 	if (IS_DAX(inode))
-		return dax_truncate_page(inode, pos, blocksize, did_zero,
-					&xfs_dax_write_iomap_ops);
-	return iomap_truncate_page(inode, pos, blocksize, did_zero,
-				   &xfs_buffered_write_iomap_ops);
+		error = dax_truncate_page(inode, pos, blocksize, did_zero,
+					  &xfs_dax_write_iomap_ops);
+	else
+		error = iomap_truncate_page(inode, pos, blocksize, did_zero,
+					    &xfs_buffered_write_iomap_ops);
+	if (error)
+		return error;
+
+	/*
+	 * Write back path won't write dirty blocks post EOF folio,
+	 * flush the entire zeroed range before updating the inode
+	 * size.
+	 */
+	return filemap_write_and_wait_range(inode->i_mapping, pos,
+					    roundup_64(pos, blocksize));
 }
diff --git a/fs/xfs/xfs_iops.c b/fs/xfs/xfs_iops.c
index 66f8c47642e8..baeeddf4a6bb 100644
--- a/fs/xfs/xfs_iops.c
+++ b/fs/xfs/xfs_iops.c
@@ -845,16 +845,6 @@ xfs_setattr_size(
 		error = xfs_zero_range(ip, oldsize, newsize - oldsize,
 				&did_zeroing);
 	} else {
-		/*
-		 * iomap won't detect a dirty page over an unwritten block (or a
-		 * cow block over a hole) and subsequently skips zeroing the
-		 * newly post-EOF portion of the page. Flush the new EOF to
-		 * convert the block before the pagecache truncate.
-		 */
-		error = filemap_write_and_wait_range(inode->i_mapping, newsize,
-						     newsize);
-		if (error)
-			return error;
 		error = xfs_truncate_page(ip, newsize, &did_zeroing);
 	}
 
-- 
2.39.2