[PATCH 4.19 3/5] fs, fscrypt: clear DCACHE_ENCRYPTED_NAME when unaliasing directory

[Eric Biggers <ebiggers@kernel.org>]

From: Eric Biggers <ebiggers@google.com>

commit 0bf3d5c1604ecbbd4e49e9f5b3c79152b87adb0d upstream.

Make __d_move() clear DCACHE_ENCRYPTED_NAME on the source dentry.  This
is needed for when d_splice_alias() moves a directory's encrypted alias
to its decrypted alias as a result of the encryption key being added.

Otherwise, the decrypted alias will incorrectly be invalidated on the
next lookup, causing problems such as unmounting a mount the user just
mount()ed there.

Note that we don't have to support arbitrary moves of this flag because
fscrypt doesn't allow dentries with DCACHE_ENCRYPTED_NAME to be the
source or target of a rename().

Fixes: 28b4c263961c ("ext4 crypto: revalidate dentry after adding or removing the key")
Reported-by: Sarthak Kukreti <sarthakkukreti@chromium.org>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
---
 fs/dcache.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/fs/dcache.c b/fs/dcache.c
index 20370a0997bf9..1897833a46685 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -2712,6 +2712,20 @@ static void copy_name(struct dentry *dentry, struct dentry *target)
 		call_rcu(&old_name->u.head, __d_free_external_name);
 }
 
+/*
+ * When d_splice_alias() moves a directory's encrypted alias to its decrypted
+ * alias as a result of the encryption key being added, DCACHE_ENCRYPTED_NAME
+ * must be cleared.  Note that we don't have to support arbitrary moves of this
+ * flag because fscrypt doesn't allow encrypted aliases to be the source or
+ * target of a rename().
+ */
+static inline void fscrypt_handle_d_move(struct dentry *dentry)
+{
+#if IS_ENABLED(CONFIG_FS_ENCRYPTION)
+	dentry->d_flags &= ~DCACHE_ENCRYPTED_NAME;
+#endif
+}
+
 /*
  * __d_move - move a dentry
  * @dentry: entry to move
@@ -2787,6 +2801,7 @@ static void __d_move(struct dentry *dentry, struct dentry *target,
 	list_move(&dentry->d_child, &dentry->d_parent->d_subdirs);
 	__d_rehash(dentry);
 	fsnotify_update_flags(dentry);
+	fscrypt_handle_d_move(dentry);
 
 	write_seqcount_end(&target->d_seq);
 	write_seqcount_end(&dentry->d_seq);
-- 
2.29.1