[PATCH v3 4/9] fscrypt: Only create hash key when needed

[Daniel Rosenberg]

If a directory isn't casefolded, it doesn't need the hash key. Skip
deriving it unless we enable it later.

Signed-off-by: Daniel Rosenberg <drosen@xxxxxxxxxx>
---
 fs/crypto/keysetup.c |  2 +-
 fs/crypto/policy.c   | 25 +++++++++++++++++++++++++
 2 files changed, 26 insertions(+), 1 deletion(-)

diff --git a/fs/crypto/keysetup.c b/fs/crypto/keysetup.c
index 7445ab76e0b32..c0db9e8d31f15 100644
--- a/fs/crypto/keysetup.c
+++ b/fs/crypto/keysetup.c
@@ -217,7 +217,7 @@ static int fscrypt_setup_v2_file_key(struct fscrypt_info *ci,
 	if (err)
 		return err;
 
-	if (S_ISDIR(ci->ci_inode->i_mode)) {
+	if (S_ISDIR(ci->ci_inode->i_mode) && IS_CASEFOLDED(ci->ci_inode)) {
 		err = fscrypt_hkdf_expand(&mk->mk_secret.hkdf,
 					  HKDF_CONTEXT_FNAME_HASH_KEY,
 					  ci->ci_nonce,
diff --git a/fs/crypto/policy.c b/fs/crypto/policy.c
index 2cd9a940d8f46..632ca355e1184 100644
--- a/fs/crypto/policy.c
+++ b/fs/crypto/policy.c
@@ -10,6 +10,7 @@
  * Modified by Eric Biggers, 2019 for v2 policy support.
  */
 
+#include <linux/key-type.h>
 #include <linux/random.h>
 #include <linux/string.h>
 #include <linux/mount.h>
@@ -591,6 +592,8 @@ int fscrypt_ioc_setflags_prepare(struct inode *inode,
 				 unsigned int flags)
 {
 	union fscrypt_policy policy;
+	struct fscrypt_info *ci;
+	struct fscrypt_master_key *mk;
 	int err;
 
 	/*
@@ -603,6 +606,28 @@ int fscrypt_ioc_setflags_prepare(struct inode *inode,
 			return err;
 		if (policy.version != FSCRYPT_POLICY_V2)
 			return -EINVAL;
+		err = fscrypt_require_key(inode);
+		if (err)
+			return err;
+		ci = inode->i_crypt_info;
+		if (ci->ci_hash_key_initialized)
+			return 0;
+		mk = ci->ci_master_key->payload.data[0];
+		down_read(&mk->mk_secret_sem);
+		if (!is_master_key_secret_present(&mk->mk_secret)) {
+			err = -ENOKEY;
+		} else {
+			err = fscrypt_hkdf_expand(&mk->mk_secret.hkdf,
+						  HKDF_CONTEXT_FNAME_HASH_KEY,
+						  ci->ci_nonce,
+						  FS_KEY_DERIVATION_NONCE_SIZE,
+						  (u8 *)&ci->ci_hash_key,
+						  sizeof(ci->ci_hash_key));
+		}
+		up_read(&mk->mk_secret_sem);
+		if (err)
+			return err;
+		ci->ci_hash_key_initialized = true;
 	}
 
 	return 0;
-- 
2.25.0.341.g760bfbb309-goog