Re: [PATCH] ocfs2: Add i_size check for dir

[Edward Adam Davis]

On Wed, 21 Aug 2024 18:41:06 +0800, Joseph Qi wrote:
>>>> When the i_size of dir is too large, it will cause limit to overflow and
>>>> be less than de_buf, ultimately resulting in last_de not being initialized
>>>> and causing uaf issue.
>>>>
>>>> Reported-and-tested-by: syzbot+5a64828fcc4c2ad9b04f@xxxxxxxxxxxxxxxxxxxxxxxxx
>>>> Signed-off-by: Edward Adam Davis <eadavis@xxxxxx>
>>>> ---
>>>>  fs/ocfs2/dir.c | 2 ++
>>>>  1 file changed, 2 insertions(+)
>>>>
>>>> diff --git a/fs/ocfs2/dir.c b/fs/ocfs2/dir.c
>>>> index d620d4c53c6f..c308dba6d213 100644
>>>> --- a/fs/ocfs2/dir.c
>>>> +++ b/fs/ocfs2/dir.c
>>>> @@ -3343,6 +3343,8 @@ static int ocfs2_find_dir_space_id(struct inode *dir, struct buffer_head *di_bh,
>>>>  	unsigned long offset = 0;
>>>>  	unsigned int rec_len, new_rec_len, free_space;
>>>>
>>>> +	if (i_size_read(dir) > OCFS2_MAX_BLOCKSIZE)
>>>> +		return -EINVAL;
>>>
>>> Why OCFS2_MAX_BLOCKSIZE?
>> I think it is largest block size in ocfs2, therefore, if it is larger
>> than it, it must be incorrect, even though the value of i_size in dir
>> in the current issue is much larger than it (i_size_read(dir) is 0x900000000000100).
>>> It seems that this is caused by a corrupted dir inode, since this is an
>>> inline case, we may try best to make sure it won't exceeds block size?
>>> i.e. dir->i_sb->s_blocksize.
>> You mean dir->i_sb->s_blocksize bigger than OCFS2_MAX_BLOCKSIZE?
>>
>No, I mean check s_blocksize seems more reasonable rather than
>OCFS2_MAX_BLOCKSIZE.
Perhaps we have different perspectives on the issue. 
My approach is to set a bottom line for the dir's i_size, and if it
exceeds the bottom line, the dir will definitely be corrupted.
And I think OCFS2_MAX_BLOCKSIZE is the reasonable bottom line.

BR,
Edward