Re: [PATCH v2] ocfs2: fix data corruption by fallocate

[Junxiao Bi <junxiao.bi@oracle.com>]

On 5/24/21 1:55 AM, Jan Kara wrote:

> On Fri 21-05-21 16:36:12, Junxiao Bi wrote:
>> 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
>>
>> Cc: <stable@vger.kernel.org>
>> Cc: Jan Kara <jack@suse.cz>
>> Signed-off-by: Junxiao Bi <junxiao.bi@oracle.com>
>> ---
>>
>> Changes in v2:
>> - suggested by Jan Kara, using sb_issue_zeroout to zero eof blocks in disk directly.
>>
>>   fs/ocfs2/file.c | 49 +++++++++++++++++++++++++++++++++++++++++++++++--
>>   1 file changed, 47 insertions(+), 2 deletions(-)
>>
>> diff --git a/fs/ocfs2/file.c b/fs/ocfs2/file.c
>> index f17c3d33fb18..17469fc7b20e 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.
> You write this here but ...
>
>> + */
>> +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;
> ... here you check actually something else and I don't see where else would
> the trimming happen.

Before the "if", end = ocfs2_align_bytes_to_clusters(sb, start), that is
the end of the cluster where "start" located.

Thanks,
Junxiao.

>
> 								Honza
>
>> +
>> +	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 +1997,11 @@ 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);
>>   	up_write(&OCFS2_I(inode)->ip_alloc_sem);
>>   	if (ret) {
>>   		mlog_errno(ret);
>> -- 
>> 2.24.3 (Apple Git-128)
>>