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

[Eric Biggers]

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@xxxxxxxxxx>
> > 
> > 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@xxxxxxxxxx>
> > ---
> >  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: