[PATCH] fscrypt: export fscrypt_d_revalidate()

[Eric Biggers <ebiggers@kernel.org>]

From: Eric Biggers <ebiggers@google.com>

Dentries that represent no-key names must have a dentry_operations that
includes fscrypt_d_revalidate().  Currently, this is handled by
fscrypt_prepare_lookup() installing fscrypt_d_ops.

However, ceph support for encryption
(https://lore.kernel.org/r/20200914191707.380444-1-jlayton@kernel.org)
can't use fscrypt_d_ops, since ceph already has its own
dentry_operations.

Similarly, ext4 and f2fs support for directories that are both encrypted
and casefolded
(https://lore.kernel.org/r/20200923010151.69506-1-drosen@google.com)
can't use fscrypt_d_ops either, since casefolding requires some dentry
operations too.

To satisfy both users, we need to move the responsibility of installing
the dentry_operations to filesystems.

In preparation for this, export fscrypt_d_revalidate() and give it a
!CONFIG_FS_ENCRYPTION stub.

Signed-off-by: Eric Biggers <ebiggers@google.com>
---

Compared to the versions of this patch from Jeff and Daniel, I've
improved the commit message and added a !CONFIG_FS_ENCRYPTION stub,
which was missing.  I'm planning to apply this for 5.10 in preparation
for both the ceph patchset and the encrypt+casefold patchset.


 fs/crypto/fname.c       | 3 ++-
 include/linux/fscrypt.h | 7 +++++++
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/fs/crypto/fname.c b/fs/crypto/fname.c
index c65979452844..1fbe6c24d705 100644
--- a/fs/crypto/fname.c
+++ b/fs/crypto/fname.c
@@ -530,7 +530,7 @@ EXPORT_SYMBOL_GPL(fscrypt_fname_siphash);
  * Validate dentries in encrypted directories to make sure we aren't potentially
  * caching stale dentries after a key has been added.
  */
-static int fscrypt_d_revalidate(struct dentry *dentry, unsigned int flags)
+int fscrypt_d_revalidate(struct dentry *dentry, unsigned int flags)
 {
 	struct dentry *dir;
 	int err;
@@ -569,6 +569,7 @@ static int fscrypt_d_revalidate(struct dentry *dentry, unsigned int flags)
 
 	return valid;
 }
+EXPORT_SYMBOL_GPL(fscrypt_d_revalidate);
 
 const struct dentry_operations fscrypt_d_ops = {
 	.d_revalidate = fscrypt_d_revalidate,
diff --git a/include/linux/fscrypt.h b/include/linux/fscrypt.h
index f1757e73162d..a8f7a43f031b 100644
--- a/include/linux/fscrypt.h
+++ b/include/linux/fscrypt.h
@@ -197,6 +197,7 @@ int fscrypt_fname_disk_to_usr(const struct inode *inode,
 bool fscrypt_match_name(const struct fscrypt_name *fname,
 			const u8 *de_name, u32 de_name_len);
 u64 fscrypt_fname_siphash(const struct inode *dir, const struct qstr *name);
+int fscrypt_d_revalidate(struct dentry *dentry, unsigned int flags);
 
 /* bio.c */
 void fscrypt_decrypt_bio(struct bio *bio);
@@ -454,6 +455,12 @@ static inline u64 fscrypt_fname_siphash(const struct inode *dir,
 	return 0;
 }
 
+static inline int fscrypt_d_revalidate(struct dentry *dentry,
+				       unsigned int flags)
+{
+	return 1;
+}
+
 /* bio.c */
 static inline void fscrypt_decrypt_bio(struct bio *bio)
 {
-- 
2.28.0