[PATCH V3] ocfs2: fix data corruption by fallocate

From: Junxiao Bi <junxiao.bi@oracle.com>
To: ocfs2-devel@oss.oracle.com
Cc: joseph.qi@linux.alibaba.com, linux-fsdevel@vger.kernel.org,
	junxiao.bi@oracle.com
Subject: [PATCH V3] ocfs2: fix data corruption by fallocate
Date: Fri, 28 May 2021 14:06:48 -0700	[thread overview]
Message-ID: <20210528210648.9124-1-junxiao.bi@oracle.com> (raw)

When fallocate punches holes out of inode size, if original isize is in
the middle of last cluster, then the part from isize to the end of the
cluster will be zeroed with buffer write, at that time isize is not
yet updated to match the new size, if writeback is kicked in, it will
invoke ocfs2_writepage()->block_write_full_page() where the pages out
of inode size will be dropped. That will cause file corruption. Fix
this by zero out eof blocks when extending the inode size.

Running the following command with qemu-image 4.2.1 can get a corrupted
coverted image file easily.

    qemu-img convert -p -t none -T none -f qcow2 $qcow_image \
             -O qcow2 -o compat=1.1 $qcow_image.conv

The usage of fallocate in qemu is like this, it first punches holes out of
inode size, then extend the inode size.

    fallocate(11, FALLOC_FL_KEEP_SIZE|FALLOC_FL_PUNCH_HOLE, 2276196352, 65536) = 0
    fallocate(11, 0, 2276196352, 65536) = 0

v1: https://www.spinics.net/lists/linux-fsdevel/msg193999.html
v2: https://lore.kernel.org/linux-fsdevel/20210525093034.GB4112@quack2.suse.cz/T/

Cc: <stable@vger.kernel.org>
Cc: Jan Kara <jack@suse.cz>
Signed-off-by: Junxiao Bi <junxiao.bi@oracle.com>
---

Changes in v3:
- move i_size_write after zeroout done, this can remove duplicated code and kill possible race.

Changes in v2:
- suggested by Jan Kara, using sb_issue_zeroout to zero eof blocks in disk directly.

 fs/ocfs2/file.c | 55 ++++++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 50 insertions(+), 5 deletions(-)

diff --git a/fs/ocfs2/file.c b/fs/ocfs2/file.c
index f17c3d33fb18..775657943057 100644
--- a/fs/ocfs2/file.c
+++ b/fs/ocfs2/file.c
@@ -1855,6 +1855,45 @@ int ocfs2_remove_inode_range(struct inode *inode,
 	return ret;
 }
 
+/*
+ * zero out partial blocks of one cluster.
+ *
+ * start: file offset where zero starts, will be made upper block aligned.
+ * len: it will be trimmed to the end of current cluster if "start + len"
+ *      is bigger than it.
+ */
+static int ocfs2_zeroout_partial_cluster(struct inode *inode,
+					u64 start, u64 len)
+{
+	int ret;
+	u64 start_block, end_block, nr_blocks;
+	u64 p_block, offset;
+	u32 cluster, p_cluster, nr_clusters;
+	struct super_block *sb = inode->i_sb;
+	u64 end = ocfs2_align_bytes_to_clusters(sb, start);
+
+	if (start + len < end)
+		end = start + len;
+
+	start_block = ocfs2_blocks_for_bytes(sb, start);
+	end_block = ocfs2_blocks_for_bytes(sb, end);
+	nr_blocks = end_block - start_block;
+	if (!nr_blocks)
+		return 0;
+
+	cluster = ocfs2_bytes_to_clusters(sb, start);
+	ret = ocfs2_get_clusters(inode, cluster, &p_cluster,
+				&nr_clusters, NULL);
+	if (ret)
+		return ret;
+	if (!p_cluster)
+		return 0;
+
+	offset = start_block - ocfs2_clusters_to_blocks(sb, cluster);
+	p_block = ocfs2_clusters_to_blocks(sb, p_cluster) + offset;
+	return sb_issue_zeroout(sb, p_block, nr_blocks, GFP_NOFS);
+}
+
 /*
  * Parts of this function taken from xfs_change_file_space()
  */
@@ -1865,7 +1904,7 @@ static int __ocfs2_change_file_space(struct file *file, struct inode *inode,
 {
 	int ret;
 	s64 llen;
-	loff_t size;
+	loff_t size, orig_isize;
 	struct ocfs2_super *osb = OCFS2_SB(inode->i_sb);
 	struct buffer_head *di_bh = NULL;
 	handle_t *handle;
@@ -1896,6 +1935,7 @@ static int __ocfs2_change_file_space(struct file *file, struct inode *inode,
 		goto out_inode_unlock;
 	}
 
+	orig_isize = i_size_read(inode);
 	switch (sr->l_whence) {
 	case 0: /*SEEK_SET*/
 		break;
@@ -1903,7 +1943,7 @@ static int __ocfs2_change_file_space(struct file *file, struct inode *inode,
 		sr->l_start += f_pos;
 		break;
 	case 2: /*SEEK_END*/
-		sr->l_start += i_size_read(inode);
+		sr->l_start += orig_isize;
 		break;
 	default:
 		ret = -EINVAL;
@@ -1957,6 +1997,14 @@ static int __ocfs2_change_file_space(struct file *file, struct inode *inode,
 	default:
 		ret = -EINVAL;
 	}
+
+	/* zeroout eof blocks in the cluster. */
+	if (!ret && change_size && orig_isize < size) {
+		ret = ocfs2_zeroout_partial_cluster(inode, orig_isize,
+					size - orig_isize);
+		if (!ret)
+			i_size_write(inode, size);
+	}
 	up_write(&OCFS2_I(inode)->ip_alloc_sem);
 	if (ret) {
 		mlog_errno(ret);
@@ -1973,9 +2021,6 @@ static int __ocfs2_change_file_space(struct file *file, struct inode *inode,
 		goto out_inode_unlock;
 	}
 
-	if (change_size && i_size_read(inode) < size)
-		i_size_write(inode, size);
-
 	inode->i_ctime = inode->i_mtime = current_time(inode);
 	ret = ocfs2_mark_inode_dirty(handle, inode, di_bh);
 	if (ret < 0)
-- 
2.24.3 (Apple Git-128)

