[RFC PATCH 1/2] fscrypt: new helper function - __fscrypt_prepare_atomic_open()

["Luís Henriques" <lhenriques@suse.de>]

This patch introduces a new helper function which prepares an atomic_open.
Because atomic open can act as a lookup if handed a dentry that is negative,
we need to set DCACHE_NOKEY_NAME if the key for the parent isn't available.

The reason for getting the encryption info before checking if the directory
has the encryption key is because we may have the key available but the
encryption info isn't yet set (maybe due to a drop_caches).  The regular
open path will use fscrypt_file_open for that but in the atomic open a
different approach is required.

Signed-off-by: Luís Henriques <lhenriques@suse.de>
---
 fs/crypto/hooks.c       | 14 ++++++++++++++
 include/linux/fscrypt.h |  6 ++++++
 2 files changed, 20 insertions(+)

diff --git a/fs/crypto/hooks.c b/fs/crypto/hooks.c
index 7b8c5a1104b5..cbb828ecc5eb 100644
--- a/fs/crypto/hooks.c
+++ b/fs/crypto/hooks.c
@@ -117,6 +117,20 @@ int __fscrypt_prepare_readdir(struct inode *dir)
 }
 EXPORT_SYMBOL_GPL(__fscrypt_prepare_readdir);
 
+int __fscrypt_prepare_atomic_open(struct inode *dir, struct dentry *dentry)
+{
+	int err = fscrypt_get_encryption_info(dir, true);
+
+	if (err || (!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_atomic_open);
+
 int __fscrypt_prepare_setattr(struct dentry *dentry, struct iattr *attr)
 {
 	if (attr->ia_valid & ATTR_SIZE)
diff --git a/include/linux/fscrypt.h b/include/linux/fscrypt.h
index 4f5f8a651213..51c4b216a625 100644
--- a/include/linux/fscrypt.h
+++ b/include/linux/fscrypt.h
@@ -362,6 +362,7 @@ int __fscrypt_prepare_rename(struct inode *old_dir, struct dentry *old_dentry,
 int __fscrypt_prepare_lookup(struct inode *dir, struct dentry *dentry,
 			     struct fscrypt_name *fname);
 int __fscrypt_prepare_readdir(struct inode *dir);
+int __fscrypt_prepare_atomic_open(struct inode *dir, struct dentry *dentry);
 int __fscrypt_prepare_setattr(struct dentry *dentry, struct iattr *attr);
 int fscrypt_prepare_setflags(struct inode *inode,
 			     unsigned int oldflags, unsigned int flags);
@@ -688,6 +689,11 @@ static inline int __fscrypt_prepare_readdir(struct inode *dir)
 	return -EOPNOTSUPP;
 }
 
+int __fscrypt_prepare_atomic_open(struct inode *dir, struct dentry *dentry)
+{
+	return -EOPNOTSUPP;
+}
+
 static inline int __fscrypt_prepare_setattr(struct dentry *dentry,
 					    struct iattr *attr)
 {