linux-kernel - Re: [f2fs-dev] [PATCH 2/6] f2fs: do not expose unwritten blocks to user by DIO

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Date:   Fri, 3 Dec 2021 14:43:07 +0800
From:   Chao Yu <chao@...nel.org>
To:     Jaegeuk Kim <jaegeuk@...nel.org>
Cc:     linux-kernel@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net
Subject: Re: [f2fs-dev] [PATCH 2/6] f2fs: do not expose unwritten blocks to
 user by DIO

On 2021/12/3 2:13, Jaegeuk Kim wrote:
> On 12/02, Chao Yu wrote:
>> On 2021/11/17 5:45, Jaegeuk Kim wrote:
>>> DIO preallocates physical blocks before writing data, but if an error occurrs
>>> or power-cut happens, we can see block contents from the disk. This patch tries
>>> to fix it by 1) turning to buffered writes for DIO into holes, 2) truncating
>>> unwritten blocks from error or power-cut.
>>>
>>> Signed-off-by: Jaegeuk Kim <jaegeuk@...nel.org>
>>> ---
>>>    fs/f2fs/data.c |  5 ++++-
>>>    fs/f2fs/f2fs.h |  5 +++++
>>>    fs/f2fs/file.c | 24 +++++++++++++++++++++++-
>>>    3 files changed, 32 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
>>> index 3b27fb7daa8b..7ac1a39fcad2 100644
>>> --- a/fs/f2fs/data.c
>>> +++ b/fs/f2fs/data.c
>>> @@ -1543,8 +1543,11 @@ int f2fs_map_blocks(struct inode *inode, struct f2fs_map_blocks *map,
>>>    					flag != F2FS_GET_BLOCK_DIO);
>>>    				err = __allocate_data_block(&dn,
>>>    							map->m_seg_type);
>>> -				if (!err)
>>> +				if (!err) {
>>> +					if (flag == F2FS_GET_BLOCK_PRE_DIO)
>>> +						file_need_truncate(inode);
>>>    					set_inode_flag(inode, FI_APPEND_WRITE);
>>> +				}
>>>    			}
>>>    			if (err)
>>>    				goto sync_out;
>>> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
>>> index be871a79c634..14bea669f87e 100644
>>> --- a/fs/f2fs/f2fs.h
>>> +++ b/fs/f2fs/f2fs.h
>>> @@ -654,6 +654,7 @@ enum {
>>>    #define FADVISE_KEEP_SIZE_BIT	0x10
>>>    #define FADVISE_HOT_BIT		0x20
>>>    #define FADVISE_VERITY_BIT	0x40
>>> +#define FADVISE_TRUNC_BIT	0x80
>>>    #define FADVISE_MODIFIABLE_BITS	(FADVISE_COLD_BIT | FADVISE_HOT_BIT)
>>> @@ -681,6 +682,10 @@ enum {
>>>    #define file_is_verity(inode)	is_file(inode, FADVISE_VERITY_BIT)
>>>    #define file_set_verity(inode)	set_file(inode, FADVISE_VERITY_BIT)
>>> +#define file_should_truncate(inode)	is_file(inode, FADVISE_TRUNC_BIT)
>>> +#define file_need_truncate(inode)	set_file(inode, FADVISE_TRUNC_BIT)
>>> +#define file_dont_truncate(inode)	clear_file(inode, FADVISE_TRUNC_BIT)
>>> +
>>>    #define DEF_DIR_LEVEL		0
>>>    enum {
>>> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
>>> index 4bf77a5bf998..ec8de0662437 100644
>>> --- a/fs/f2fs/file.c
>>> +++ b/fs/f2fs/file.c
>>> @@ -960,10 +960,21 @@ int f2fs_setattr(struct user_namespace *mnt_userns, struct dentry *dentry,
>>>    		down_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
>>>    		filemap_invalidate_lock(inode->i_mapping);
>>> +		/*
>>> +		 * Truncate stale preallocated blocks used by the previous DIO.
>>> +		 */
>>> +		if (file_should_truncate(inode)) {
>>> +			err = f2fs_truncate(inode);
>>> +			if (err)
>>> +				goto out_unlock;
>>> +			file_dont_truncate(inode);
>>> +		}
>>> +
>>>    		truncate_setsize(inode, attr->ia_size);
>>>    		if (attr->ia_size <= old_size)
>>>    			err = f2fs_truncate(inode);
>>> +out_unlock:
>>>    		/*
>>>    		 * do not trim all blocks after i_size if target size is
>>>    		 * larger than i_size.
>>> @@ -4257,6 +4268,13 @@ static int f2fs_preallocate_blocks(struct kiocb *iocb, struct iov_iter *iter)
>>>    	/* If it will be an out-of-place direct write, don't bother. */
>>>    	if (dio && f2fs_lfs_mode(sbi))
>>>    		return 0;
>>> +	/*
>>> +	 * Don't preallocate holes aligned to DIO_SKIP_HOLES which turns into
>>> +	 * buffered IO, if DIO meets any holes.
>>> +	 */
>>> +	if (dio && i_size_read(inode) &&
>>> +		(F2FS_BYTES_TO_BLK(pos) < F2FS_BLK_ALIGN(i_size_read(inode))))
>>> +		return 0;
>>>    	/* No-wait I/O can't allocate blocks. */
>>>    	if (iocb->ki_flags & IOCB_NOWAIT)
>>> @@ -4366,10 +4384,14 @@ static ssize_t f2fs_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
>>>    		if (preallocated > 0 && i_size_read(inode) < target_size) {
>>>    			down_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
>>>    			filemap_invalidate_lock(inode->i_mapping);
>>> -			f2fs_truncate(inode);
>>> +			if (!f2fs_truncate(inode))
>>> +				file_dont_truncate(inode);
>>>    			filemap_invalidate_unlock(inode->i_mapping);
>>>    			up_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
>>> +		} else {
>>> +			file_dont_truncate(inode);
>>
>> How about this case:
>>
>> - touch file
>> - DIO write [0, 8kb] to file
>>   - preallocate 2 physical blocks
>>   - set FADVISE_TRUNC_BIT
>>   - SPO
>> - BUFIO write [0, 4kb] to file
>>   - file_dont_truncate -- it leaks unwritten [4kb, 8kb] to user after
>> truncating file to 8kb
> 
> i_size should be 4kb, no?

- BUFIO write [0, 4kb] to file
  - file_dont_truncate()
i_size should be 4kb, w/ FADVISE_TRUNC_BIT

- setattr 8kb
i_size should be 8kb, last [4kb, 8kb] is unwritten

Thanks,

> 
>>
>> Thanks,
>>
>>>    		}
>>> +
>>>    		clear_inode_flag(inode, FI_PREALLOCATED_ALL);
>>>    		if (ret > 0)
>>>