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Subject: Re: [PATCH v2] vfs: only allow SETFLAGS to set DAX flag on files and
 dirs
To:     "Darrick J. Wong" <djwong@kernel.org>
Cc:     viro@zeniv.linux.org.uk, linux-fsdevel@vger.kernel.org,
        linux-ext4@vger.kernel.org
References: <20210719023834.104053-1-jefflexu@linux.alibaba.com>
 <20210719174331.GH22357@magnolia>
From:   JeffleXu <jefflexu@linux.alibaba.com>
Message-ID: <729b4efa-8903-c5ec-4e29-7f4e0d02ce2a@linux.alibaba.com>
Date:   Tue, 20 Jul 2021 15:33:20 +0800
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On 7/20/21 1:43 AM, Darrick J. Wong wrote:
> On Mon, Jul 19, 2021 at 10:38:34AM +0800, Jeffle Xu wrote:
>> This is similar to commit dbc77f31e58b ("vfs: only allow FSSETXATTR to
>> set DAX flag on files and dirs").
>>
>> Though the underlying filesystems may have filtered invalid flags, e.g.,
>> ext4_mask_flags() called in ext4_fileattr_set(), also check it in VFS
>> layer.
>>
>> Signed-off-by: Jeffle Xu <jefflexu@linux.alibaba.com>
>> ---
>> changes since v1:
>> - add separate parentheses surrounding flag tests
>> ---
>>  fs/ioctl.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/fs/ioctl.c b/fs/ioctl.c
>> index 1e2204fa9963..90cfaa4db03a 100644
>> --- a/fs/ioctl.c
>> +++ b/fs/ioctl.c
>> @@ -835,7 +835,7 @@ static int fileattr_set_prepare(struct inode *inode,
>>  	 * It is only valid to set the DAX flag on regular files and
>>  	 * directories on filesystems.
>>  	 */
>> -	if ((fa->fsx_xflags & FS_XFLAG_DAX) &&
>> +	if (((fa->fsx_xflags & FS_XFLAG_DAX) || (fa->flags & FS_DAX_FL)) &&
> 
> Isn't fileattr_fill_flags supposed to fill out fa->fsx_xflags from
> fa->flags for a SETFLAGS call?

Yes, but fa->fsx_xflags inherited from fa->flags (at least in ext4 it
is) is the original flags/xflags of the file before SETFLAG/FSSETXATTR.
Here we want to check *new* flags/xflags.

> 
>>  	    !(S_ISREG(inode->i_mode) || S_ISDIR(inode->i_mode)))
>>  		return -EINVAL;
>>  
>> -- 
>> 2.27.0
>>

-- 
Thanks,
Jeffle