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Subject: Re: [PATCH 3/6] fs-verity: add FS_IOC_READ_VERITY_METADATA ioctl
To:     Eric Biggers <ebiggers@kernel.org>
CC:     <linux-fscrypt@vger.kernel.org>, Theodore Ts'o <tytso@mit.edu>,
        <linux-api@vger.kernel.org>,
        <linux-f2fs-devel@lists.sourceforge.net>,
        <linux-fsdevel@vger.kernel.org>, Jaegeuk Kim <jaegeuk@kernel.org>,
        <linux-ext4@vger.kernel.org>, Victor Hsieh <victorhsieh@google.com>
References: <20210115181819.34732-1-ebiggers@kernel.org>
 <20210115181819.34732-4-ebiggers@kernel.org>
 <107cf2f2-a6fe-57c2-d17d-57679d7c612d@huawei.com>
 <YB+ead3SvsQy5ULH@sol.localdomain>
From:   Chao Yu <yuchao0@huawei.com>
Message-ID: <fbe787cc-fcba-7c97-d5ca-cb67345d0c8c@huawei.com>
Date:   Sun, 7 Feb 2021 16:32:17 +0800
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On 2021/2/7 16:01, Eric Biggers wrote:
> On Sun, Feb 07, 2021 at 03:46:43PM +0800, Chao Yu wrote:
>> Hi Eric,
>>
>> On 2021/1/16 2:18, Eric Biggers wrote:
>>> +static int f2fs_ioc_read_verity_metadata(struct file *filp, unsigned long arg)
>>> +{
>>> +	if (!f2fs_sb_has_verity(F2FS_I_SB(file_inode(filp))))
>>> +		return -EOPNOTSUPP;
>>
>> One case is after we update kernel image, f2fs module may no longer support
>> compress algorithm which current file was compressed with, to avoid triggering
>> IO with empty compress engine (struct f2fs_compress_ops pointer):
>>
>> It needs to add f2fs_is_compress_backend_ready() check condition here?
>>
>> Thanks,
>>
>>> +
>>> +	return fsverity_ioctl_read_metadata(filp, (const void __user *)arg);
>>> +}
> 
> In that case it wouldn't have been possible to open the file, because
> f2fs_file_open() checks for it.  So it's not necessary to repeat the same check
> in every operation on the file descriptor.

Oh, yes, it's safe now.

I'm thinking we need to remove the check in f2fs_file_open(), because the check
will fail metadata access/update (via f{g,s}etxattr/ioctl), however original
intention of that check is only to avoid syscalls to touch compressed data w/o
the engine, anyway this is another topic.

The whole patchset looks fine to me, feel free to add:

Reviewed-by: Chao Yu <yuchao0@huawei.com>

Thanks,

> 
> - Eric
> .
>