[v2,0/8] Revert setting casefolding dentry operations through s_d_op

Message

Gabriel Krisman Bertazi Dec. 15, 2023, 9:16 p.m. UTC

[Apologies for the quick spin of a v2.  The only difference are a couple
fixes to the build when CONFIG_UNICODE=n caught by LKP and detailed in
each patch changelog.]

When case-insensitive and fscrypt were adapted to work together, we moved the
code that sets the dentry operations for case-insensitive dentries(d_hash and
d_compare) to happen from a helper inside ->lookup.  This is because fscrypt
wants to set d_revalidate only on some dentries, so it does it only for them in
d_revalidate.

But, case-insensitive hooks are actually set on all dentries in the filesystem,
so the natural place to do it is through s_d_op and let d_alloc handle it [1].
In addition, doing it inside the ->lookup is a problem for case-insensitive
dentries that are not created through ->lookup, like those coming
open-by-fhandle[2], which will not see the required d_ops.

This patchset therefore reverts to using sb->s_d_op to set the dentry operations
for case-insensitive filesystems.  In order to set case-insensitive hooks early
and not require every dentry to have d_revalidate in case-insensitive
filesystems, it introduces a patch suggested by Al Viro to disable d_revalidate
on some dentries on the fly.

It survives fstests encrypt and quick groups without regressions.  Based on
v6.7-rc1.

[1] https://lore.kernel.org/linux-fsdevel/20231123195327.GP38156@ZenIV/
[2] https://lore.kernel.org/linux-fsdevel/20231123171255.GN38156@ZenIV/

Gabriel Krisman Bertazi (8):
  dcache: Add helper to disable d_revalidate for a specific dentry
  fscrypt: Drop d_revalidate if key is available
  libfs: Merge encrypted_ci_dentry_ops and ci_dentry_ops
  libfs: Expose generic_ci_dentry_ops outside of libfs
  ext4: Set the case-insensitive dentry operations through ->s_d_op
  f2fs: Set the case-insensitive dentry operations through ->s_d_op
  libfs: Don't support setting casefold operations during lookup
  fscrypt: Move d_revalidate configuration back into fscrypt

 fs/crypto/fname.c       |  9 +++++-
 fs/crypto/hooks.c       |  8 +++++
 fs/dcache.c             | 10 +++++++
 fs/ext4/namei.c         |  1 -
 fs/ext4/super.c         |  5 ++++
 fs/f2fs/namei.c         |  1 -
 fs/f2fs/super.c         |  5 ++++
 fs/libfs.c              | 66 ++---------------------------------------
 fs/ubifs/dir.c          |  1 -
 include/linux/dcache.h  |  1 +
 include/linux/fs.h      |  2 +-
 include/linux/fscrypt.h | 10 +++----
 12 files changed, 45 insertions(+), 74 deletions(-)

Comments

Eric Biggers Dec. 19, 2023, 11:12 p.m. UTC | #1

On Fri, Dec 15, 2023 at 04:16:00PM -0500, Gabriel Krisman Bertazi wrote:
> [Apologies for the quick spin of a v2.  The only difference are a couple
> fixes to the build when CONFIG_UNICODE=n caught by LKP and detailed in
> each patch changelog.]
> 
> When case-insensitive and fscrypt were adapted to work together, we moved the
> code that sets the dentry operations for case-insensitive dentries(d_hash and
> d_compare) to happen from a helper inside ->lookup.  This is because fscrypt
> wants to set d_revalidate only on some dentries, so it does it only for them in
> d_revalidate.
> 
> But, case-insensitive hooks are actually set on all dentries in the filesystem,
> so the natural place to do it is through s_d_op and let d_alloc handle it [1].
> In addition, doing it inside the ->lookup is a problem for case-insensitive
> dentries that are not created through ->lookup, like those coming
> open-by-fhandle[2], which will not see the required d_ops.
> 
> This patchset therefore reverts to using sb->s_d_op to set the dentry operations
> for case-insensitive filesystems.  In order to set case-insensitive hooks early
> and not require every dentry to have d_revalidate in case-insensitive
> filesystems, it introduces a patch suggested by Al Viro to disable d_revalidate
> on some dentries on the fly.
> 
> It survives fstests encrypt and quick groups without regressions.  Based on
> v6.7-rc1.
> 
> [1] https://lore.kernel.org/linux-fsdevel/20231123195327.GP38156@ZenIV/
> [2] https://lore.kernel.org/linux-fsdevel/20231123171255.GN38156@ZenIV/
> 
> Gabriel Krisman Bertazi (8):
>   dcache: Add helper to disable d_revalidate for a specific dentry
>   fscrypt: Drop d_revalidate if key is available
>   libfs: Merge encrypted_ci_dentry_ops and ci_dentry_ops
>   libfs: Expose generic_ci_dentry_ops outside of libfs
>   ext4: Set the case-insensitive dentry operations through ->s_d_op
>   f2fs: Set the case-insensitive dentry operations through ->s_d_op
>   libfs: Don't support setting casefold operations during lookup
>   fscrypt: Move d_revalidate configuration back into fscrypt

Thanks Gabriel, this series looks good.  Sorry that we missed this when adding
the support for encrypt+casefold.

It's slightly awkward that some lines of code added by patches 5-6 are removed
in patch 8.  These changes look very hard to split up, though, so you've
probably done about the best that can be done.

One question/request: besides performance, the other reason we're so careful
about minimizing when ->d_revalidate is set for fscrypt is so that overlayfs
works on encrypted directories.  This is because overlayfs is not compatible
with ->d_revalidate.  I think your solution still works for that, since
DCACHE_OP_REVALIDATE will be cleared after the first call to
fscrypt_d_revalidate(), and when checking for usupported dentries overlayfs does
indeed check for DCACHE_OP_REVALIDATE instead of ->d_revalidate directly.
However, that does rely on that very first call to ->d_revalidate actually
happening before the check is done.  It would be nice to verify that
overlayfs+fscrypt indeed continues to work, and explicitly mention this
somewhere (I don't see any mention of overlayfs+fscrypt in the series).

- Eric