linux-ext4 - Re: [PATCH v4 2/3] fscrypt: Have filesystems handle their d

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Date:   Tue, 24 Nov 2020 10:08:24 +0800
From:   Gao Xiang <hsiangkao@...hat.com>
To:     Eric Biggers <ebiggers@...nel.org>
Cc:     Gabriel Krisman Bertazi <krisman@...labora.com>,
        Daniel Rosenberg <drosen@...gle.com>,
        "Theodore Y . Ts'o" <tytso@....edu>,
        Jaegeuk Kim <jaegeuk@...nel.org>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        Chao Yu <chao@...nel.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Richard Weinberger <richard@....at>,
        linux-fscrypt@...r.kernel.org, linux-ext4@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-mtd@...ts.infradead.org, kernel-team@...roid.com
Subject: Re: [PATCH v4 2/3] fscrypt: Have filesystems handle their d_ops

On Mon, Nov 23, 2020 at 02:51:44PM -0800, Eric Biggers wrote:
> On Sun, Nov 22, 2020 at 01:12:18PM +0800, Gao Xiang wrote:
> > Hi all,
> > 
> > On Thu, Nov 19, 2020 at 06:09:03AM +0000, Daniel Rosenberg wrote:
> > > This shifts the responsibility of setting up dentry operations from
> > > fscrypt to the individual filesystems, allowing them to have their own
> > > operations while still setting fscrypt's d_revalidate as appropriate.
> > > 
> > > Most filesystems can just use generic_set_encrypted_ci_d_ops, unless
> > > they have their own specific dentry operations as well. That operation
> > > will set the minimal d_ops required under the circumstances.
> > > 
> > > Since the fscrypt d_ops are set later on, we must set all d_ops there,
> > > since we cannot adjust those later on. This should not result in any
> > > change in behavior.
> > > 
> > > Signed-off-by: Daniel Rosenberg <drosen@...gle.com>
> > > Acked-by: Eric Biggers <ebiggers@...gle.com>
> > > ---
> > 
> > ...
> > 
> > >  extern const struct file_operations ext4_dir_operations;
> > >  
> > > -#ifdef CONFIG_UNICODE
> > > -extern const struct dentry_operations ext4_dentry_ops;
> > > -#endif
> > > -
> > >  /* file.c */
> > >  extern const struct inode_operations ext4_file_inode_operations;
> > >  extern const struct file_operations ext4_file_operations;
> > > diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
> > > index 33509266f5a0..12a417ff5648 100644
> > > --- a/fs/ext4/namei.c
> > > +++ b/fs/ext4/namei.c
> > > @@ -1614,6 +1614,7 @@ static struct buffer_head *ext4_lookup_entry(struct inode *dir,
> > >  	struct buffer_head *bh;
> > >  
> > >  	err = ext4_fname_prepare_lookup(dir, dentry, &fname);
> > > +	generic_set_encrypted_ci_d_ops(dentry);
> > 
> > One thing might be worth noticing is that currently overlayfs might
> > not work properly when dentry->d_sb->s_encoding is set even only some
> > subdirs are CI-enabled but the others not, see generic_set_encrypted_ci_d_ops(),
> > ovl_mount_dir_noesc => ovl_dentry_weird()
> > 
> > For more details, see:
> > https://android-review.googlesource.com/c/device/linaro/hikey/+/1483316/2#message-2e1f6ab0010a3e35e7d8effea73f60341f84ee4d
> > 
> > Just found it by chance (and not sure if it's vital for now), and
> > a kind reminder about this.
> > 
> 
> Yes, overlayfs doesn't work on ext4 or f2fs filesystems that have the casefold
> feature enabled, regardless of which directories are actually using casefolding.
> This is an existing limitation which was previously discussed, e.g. at
> https://lkml.kernel.org/linux-ext4/CAOQ4uxgPXBazE-g2v=T_vOvnr_f0ZHyKYZ4wvn7A3ePatZrhnQ@mail.gmail.com/T/#u
> and
> https://lkml.kernel.org/linux-ext4/20191203051049.44573-1-drosen@google.com/T/#u.
> 
> Gabriel and Daniel, is one of you still looking into fixing this?  IIUC, the
> current thinking is that when the casefolding flag is set on a directory, it's
> too late to assign dentry_operations at that point.  But what if all child
> dentries (which must be negative) are invalidated first, and also the filesystem
> forbids setting the casefold flag on encrypted directories that are accessed via
> a no-key name (so that fscrypt_d_revalidate isn't needed -- i.e. the directory
> would only go from "no d_ops" to "generic_ci_dentry_ops", not from
> "generic_encrypted_dentry_ops" to "generic_encrypted_ci_dentry_ops")?

>From my limited knowledge about VFS, I think that is practical as well, since
we don't have sub-sub-dirs since all sub-dirs are negative dentries for empty dirs.
And if casefold ioctl is "dir inode locked", I think that would be fine (?)
I don't check the code though.

Thanks,
Gao Xiang

> 
> - Eric
>