fscrypt: new helper function - fscrypt_prepare_lookup_partial()

This patch introduces a new helper function which can be used both in
lookups and in atomic_open operations by filesystems that want to handle
filename encryption and no-key dentries themselves.

The reason for this function to be used in atomic open is that this
operation can act as a lookup if handed a dentry that is negative.  And in
this case we may need to set DCACHE_NOKEY_NAME.

Signed-off-by: Luís Henriques <lhenriques@suse.de>
Tested-by: Xiubo Li <xiubli@redhat.com>
Reviewed-by: Xiubo Li <xiubli@redhat.com>
[ebiggers: improved the function comment, and moved the function to just
           below __fscrypt_prepare_lookup()]
Link: https://lore.kernel.org/r/20230320220149.21863-1-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>

diff --git a/fs/crypto/hooks.c b/fs/crypto/hooks.c
index 7b8c5a1104b5867e292c4c2a31d11c93d1925d30..9151934c50866761ed3a235cd265ad7beeffb02c 100644 (file)
--- a/fs/crypto/hooks.c
+++ b/fs/crypto/hooks.c
@@ -111,6 +111,36 @@ int __fscrypt_prepare_lookup(struct inode *dir, struct dentry *dentry,
 }
 EXPORT_SYMBOL_GPL(__fscrypt_prepare_lookup);
 
+/**
+ * fscrypt_prepare_lookup_partial() - prepare lookup without filename setup
+ * @dir: the encrypted directory being searched
+ * @dentry: the dentry being looked up in @dir
+ *
+ * This function should be used by the ->lookup and ->atomic_open methods of
+ * filesystems that handle filename encryption and no-key name encoding
+ * themselves and thus can't use fscrypt_prepare_lookup().  Like
+ * fscrypt_prepare_lookup(), this will try to set up the directory's encryption
+ * key and will set DCACHE_NOKEY_NAME on the dentry if the key is unavailable.
+ * However, this function doesn't set up a struct fscrypt_name for the filename.
+ *
+ * Return: 0 on success; -errno on error.  Note that the encryption key being
+ *        unavailable is not considered an error.  It is also not an error if
+ *        the encryption policy is unsupported by this kernel; that is treated
+ *        like the key being unavailable, so that files can still be deleted.
+ */
+int fscrypt_prepare_lookup_partial(struct inode *dir, struct dentry *dentry)
+{
+       int err = fscrypt_get_encryption_info(dir, true);
+
+       if (!err && !fscrypt_has_encryption_key(dir)) {
+               spin_lock(&dentry->d_lock);
+               dentry->d_flags |= DCACHE_NOKEY_NAME;
+               spin_unlock(&dentry->d_lock);
+       }
+       return err;
+}
+EXPORT_SYMBOL_GPL(fscrypt_prepare_lookup_partial);
+
 int __fscrypt_prepare_readdir(struct inode *dir)
 {
        return fscrypt_get_encryption_info(dir, true);

diff --git a/include/linux/fscrypt.h b/include/linux/fscrypt.h
index e0a49c3125ebc22ada8092c88c5009d2dadad429..a69f1302051d3c37b23a198dc0457b9081f05488 100644 (file)
--- a/include/linux/fscrypt.h
+++ b/include/linux/fscrypt.h
@@ -359,6 +359,7 @@ int __fscrypt_prepare_rename(struct inode *old_dir, struct dentry *old_dentry,
                             unsigned int flags);
 int __fscrypt_prepare_lookup(struct inode *dir, struct dentry *dentry,
                             struct fscrypt_name *fname);
+int fscrypt_prepare_lookup_partial(struct inode *dir, struct dentry *dentry);
 int __fscrypt_prepare_readdir(struct inode *dir);
 int __fscrypt_prepare_setattr(struct dentry *dentry, struct iattr *attr);
 int fscrypt_prepare_setflags(struct inode *inode,
@@ -673,6 +674,12 @@ static inline int __fscrypt_prepare_lookup(struct inode *dir,
        return -EOPNOTSUPP;
 }
 
+static inline int fscrypt_prepare_lookup_partial(struct inode *dir,
+                                                struct dentry *dentry)
+{
+       return -EOPNOTSUPP;
+}
+
 static inline int __fscrypt_prepare_readdir(struct inode *dir)
 {
        return -EOPNOTSUPP;