fscrypt: Switch to sync_skcipher and on-stack requests

Now that fscrypt uses only synchronous skciphers, switch to the actual
sync_skcipher API and the corresponding on-stack requests.  This
eliminates a heap allocation per en/decryption operation.

Link: https://lore.kernel.org/r/20250710060754.637098-4-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@kernel.org>

1 files changed, 17 insertions, 36 deletions

diff --git a/fs/crypto/fname.c b/fs/crypto/fname.c
index 17edc24ccd42..f9f6713e144f 100644
--- a/fs/crypto/fname.c
+++ b/fs/crypto/fname.c
@@ -94,12 +94,12 @@ static inline bool fscrypt_is_dot_dotdot(const struct qstr *str)
 int fscrypt_fname_encrypt(const struct inode *inode, const struct qstr *iname,
 			  u8 *out, unsigned int olen)
 {
-	struct skcipher_request *req = NULL;
 	const struct fscrypt_inode_info *ci = inode->i_crypt_info;
-	struct crypto_skcipher *tfm = ci->ci_enc_key.tfm;
+	struct crypto_sync_skcipher *tfm = ci->ci_enc_key.tfm;
+	SYNC_SKCIPHER_REQUEST_ON_STACK(req, tfm);
 	union fscrypt_iv iv;
 	struct scatterlist sg;
-	int res;
+	int err;
 
 	/*
 	 * Copy the filename to the output buffer for encrypting in-place and
@@ -110,28 +110,17 @@ int fscrypt_fname_encrypt(const struct inode *inode, const struct qstr *iname,
 	memcpy(out, iname->name, iname->len);
 	memset(out + iname->len, 0, olen - iname->len);
 
-	/* Initialize the IV */
 	fscrypt_generate_iv(&iv, 0, ci);
 
-	/* Set up the encryption request */
-	req = skcipher_request_alloc(tfm, GFP_NOFS);
-	if (!req)
-		return -ENOMEM;
 	skcipher_request_set_callback(
 		req, CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
 		NULL, NULL);
 	sg_init_one(&sg, out, olen);
 	skcipher_request_set_crypt(req, &sg, &sg, olen, &iv);
-
-	/* Do the encryption */
-	res = crypto_skcipher_encrypt(req);
-	skcipher_request_free(req);
-	if (res < 0) {
-		fscrypt_err(inode, "Filename encryption failed: %d", res);
-		return res;
-	}
-
-	return 0;
+	err = crypto_skcipher_encrypt(req);
+	if (err)
+		fscrypt_err(inode, "Filename encryption failed: %d", err);
+	return err;
 }
 EXPORT_SYMBOL_GPL(fscrypt_fname_encrypt);
 
@@ -149,33 +138,25 @@ static int fname_decrypt(const struct inode *inode,
 			 const struct fscrypt_str *iname,
 			 struct fscrypt_str *oname)
 {
-	struct skcipher_request *req = NULL;
-	struct scatterlist src_sg, dst_sg;
 	const struct fscrypt_inode_info *ci = inode->i_crypt_info;
-	struct crypto_skcipher *tfm = ci->ci_enc_key.tfm;
+	struct crypto_sync_skcipher *tfm = ci->ci_enc_key.tfm;
+	SYNC_SKCIPHER_REQUEST_ON_STACK(req, tfm);
 	union fscrypt_iv iv;
-	int res;
+	struct scatterlist src_sg, dst_sg;
+	int err;
+
+	fscrypt_generate_iv(&iv, 0, ci);
 
-	/* Allocate request */
-	req = skcipher_request_alloc(tfm, GFP_NOFS);
-	if (!req)
-		return -ENOMEM;
 	skcipher_request_set_callback(
 		req, CRYPTO_TFM_REQ_MAY_BACKLOG | CRYPTO_TFM_REQ_MAY_SLEEP,
 		NULL, NULL);
-
-	/* Initialize IV */
-	fscrypt_generate_iv(&iv, 0, ci);
-
-	/* Create decryption request */
 	sg_init_one(&src_sg, iname->name, iname->len);
 	sg_init_one(&dst_sg, oname->name, oname->len);
 	skcipher_request_set_crypt(req, &src_sg, &dst_sg, iname->len, &iv);
-	res = crypto_skcipher_decrypt(req);
-	skcipher_request_free(req);
-	if (res < 0) {
-		fscrypt_err(inode, "Filename decryption failed: %d", res);
-		return res;
+	err = crypto_skcipher_decrypt(req);
+	if (err) {
+		fscrypt_err(inode, "Filename decryption failed: %d", err);
+		return err;
 	}
 
 	oname->len = strnlen(oname->name, iname->len);