Re: [PATCH] ext4 crypto: fix to check feature status before get policy

[Chao Yu <yuchao0@huawei.com>]

On 2019/8/31 23:02, Eric Biggers wrote:
> On Sat, Aug 31, 2019 at 06:32:28PM +0800, Chao Yu wrote:
>> Hi,
>>
>> Is this change not necessary? A month has passed...
>>
>> Thanks,
>>
>> On 2019/8/4 17:56, Chao Yu wrote:
>>> From: Chao Yu <yuchao0@huawei.com>
>>>
>>> When getting fscrypto policy via EXT4_IOC_GET_ENCRYPTION_POLICY, if
>>> encryption feature is off, it's better to return EOPNOTSUPP instead
>>> of ENODATA, so let's add ext4_has_feature_encrypt() to do the check
>>> for that.
>>>
>>> Signed-off-by: Chao Yu <yuchao0@huawei.com>
>>> ---
>>>  fs/ext4/ioctl.c | 6 ++++--
>>>  1 file changed, 4 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/fs/ext4/ioctl.c b/fs/ext4/ioctl.c
>>> index 442f7ef873fc..bf87835c1237 100644
>>> --- a/fs/ext4/ioctl.c
>>> +++ b/fs/ext4/ioctl.c
>>> @@ -1112,9 +1112,11 @@ long ext4_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
>>>  		return -EOPNOTSUPP;
>>>  #endif
>>>  	}
>>> -	case EXT4_IOC_GET_ENCRYPTION_POLICY:
>>> +	case EXT4_IOC_GET_ENCRYPTION_POLICY: {
>>> +		if (!ext4_has_feature_encrypt(sb))
>>> +			return -EOPNOTSUPP;
>>>  		return fscrypt_ioctl_get_policy(filp, (void __user *)arg);
>>> -
>>> +	}
>>>  	case EXT4_IOC_FSGETXATTR:
>>>  	{
>>>  		struct fsxattr fa;
>>>
> 
> Sorry, I was preoccupied with all the other fscrypt changes, and was thinking of
> waiting until 5.5 for this to avoid a potential extra merge conflict or a
> potentially breaking change.  Looking at this again though, the new ioctl
> FS_IOC_GET_ENCRYPTION_POLICY_EX *does* do the feature check, which doesn't match
> the documentation, which implies the check isn't done.  Also, f2fs does the
> check in FS_IOC_GET_ENCRYPTION_POLICY, so the filesystems are inconsistent.
> 
> So, it makes some sense to apply this now.  So I've gone ahead and applied the
> following to fscrypt.git#master, edited a bit from your original patch:
> 
>>>From 0642ea2409f3bfa105570e12854b8e2628db6835 Mon Sep 17 00:00:00 2001
> From: Chao Yu <yuchao0@huawei.com>
> Date: Sun, 4 Aug 2019 17:56:43 +0800
> Subject: [PATCH] ext4 crypto: fix to check feature status before get policy
> 
> When getting fscrypt policy via EXT4_IOC_GET_ENCRYPTION_POLICY, if
> encryption feature is off, it's better to return EOPNOTSUPP instead of
> ENODATA, so let's add ext4_has_feature_encrypt() to do the check for
> that.
> 
> This makes it so that all fscrypt ioctls consistently check for the
> encryption feature, and makes ext4 consistent with f2fs in this regard.
> 
> Signed-off-by: Chao Yu <yuchao0@huawei.com>
> [EB - removed unneeded braces, updated the documentation, and
>       added more explanation to commit message]

The patch looks better now, thanks for the help.

Thanks,

> Signed-off-by: Eric Biggers <ebiggers@google.com>
> ---
>  Documentation/filesystems/fscrypt.rst | 3 ++-
>  fs/ext4/ioctl.c                       | 2 ++
>  2 files changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/filesystems/fscrypt.rst b/Documentation/filesystems/fscrypt.rst
> index 4289c29d7c5a..8a0700af9596 100644
> --- a/Documentation/filesystems/fscrypt.rst
> +++ b/Documentation/filesystems/fscrypt.rst
> @@ -562,7 +562,8 @@ FS_IOC_GET_ENCRYPTION_POLICY_EX can fail with the following errors:
>    or this kernel is too old to support FS_IOC_GET_ENCRYPTION_POLICY_EX
>    (try FS_IOC_GET_ENCRYPTION_POLICY instead)
>  - ``EOPNOTSUPP``: the kernel was not configured with encryption
> -  support for this filesystem
> +  support for this filesystem, or the filesystem superblock has not
> +  had encryption enabled on it
>  - ``EOVERFLOW``: the file is encrypted and uses a recognized
>    encryption policy version, but the policy struct does not fit into
>    the provided buffer
> diff --git a/fs/ext4/ioctl.c b/fs/ext4/ioctl.c
> index fe5a4b13f939..5703d607f5af 100644
> --- a/fs/ext4/ioctl.c
> +++ b/fs/ext4/ioctl.c
> @@ -1113,6 +1113,8 @@ long ext4_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
>  #endif
>  	}
>  	case EXT4_IOC_GET_ENCRYPTION_POLICY:
> +		if (!ext4_has_feature_encrypt(sb))
> +			return -EOPNOTSUPP;
>  		return fscrypt_ioctl_get_policy(filp, (void __user *)arg);
>  
>  	case FS_IOC_GET_ENCRYPTION_POLICY_EX:
>