linux-kernel - [PATCH 2/8] smb: client: Use HMAC-SHA256 library for key generation

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Message-ID: <20251012015738.244315-3-ebiggers@kernel.org>
Date: Sat, 11 Oct 2025 18:57:32 -0700
From: Eric Biggers <ebiggers@...nel.org>
To: linux-cifs@...r.kernel.org,
	Steve French <sfrench@...ba.org>
Cc: samba-technical@...ts.samba.org,
	linux-crypto@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Paulo Alcantara <pc@...guebit.org>,
	Ronnie Sahlberg <ronniesahlberg@...il.com>,
	Shyam Prasad N <sprasad@...rosoft.com>,
	Tom Talpey <tom@...pey.com>,
	Bharath SM <bharathsm@...rosoft.com>,
	Eric Biggers <ebiggers@...nel.org>
Subject: [PATCH 2/8] smb: client: Use HMAC-SHA256 library for key generation

Convert generate_key() to use the HMAC-SHA256 library instead of a
"hmac(sha256)" crypto_shash.  This is simpler and faster.  With the
library there's no need to allocate memory, no need to handle errors,
and the HMAC-SHA256 code is accessed directly without inefficient
indirect calls and other unnecessary API overhead.

Also remove the unnecessary 'hashptr' variable.

For now smb3_crypto_shash_allocate() still allocates a "hmac(sha256)"
crypto_shash.  It will be removed in a later commit.

Signed-off-by: Eric Biggers <ebiggers@...nel.org>
---
 fs/smb/client/Kconfig         |  1 +
 fs/smb/client/smb2transport.c | 68 ++++++++---------------------------
 2 files changed, 15 insertions(+), 54 deletions(-)

diff --git a/fs/smb/client/Kconfig b/fs/smb/client/Kconfig
index 4ac79ff5649bf..f0c1ff8544f67 100644
--- a/fs/smb/client/Kconfig
+++ b/fs/smb/client/Kconfig
@@ -14,10 +14,11 @@ config CIFS
 	select CRYPTO_CCM
 	select CRYPTO_GCM
 	select CRYPTO_ECB
 	select CRYPTO_AES
 	select CRYPTO_LIB_ARC4
+	select CRYPTO_LIB_SHA256
 	select CRYPTO_LIB_SHA512
 	select KEYS
 	select DNS_RESOLVER
 	select ASN1
 	select OID_REGISTRY
diff --git a/fs/smb/client/smb2transport.c b/fs/smb/client/smb2transport.c
index 33f33013b3927..bde96eace8c94 100644
--- a/fs/smb/client/smb2transport.c
+++ b/fs/smb/client/smb2transport.c
@@ -17,10 +17,11 @@
 #include <linux/uaccess.h>
 #include <asm/processor.h>
 #include <linux/mempool.h>
 #include <linux/highmem.h>
 #include <crypto/aead.h>
+#include <crypto/sha2.h>
 #include "cifsglob.h"
 #include "cifsproto.h"
 #include "smb2proto.h"
 #include "cifs_debug.h"
 #include "../common/smb2status.h"
@@ -334,80 +335,39 @@ static int generate_key(struct cifs_ses *ses, struct kvec label,
 	__u8 i[4] = {0, 0, 0, 1};
 	__u8 L128[4] = {0, 0, 0, 128};
 	__u8 L256[4] = {0, 0, 1, 0};
 	int rc = 0;
 	unsigned char prfhash[SMB2_HMACSHA256_SIZE];
-	unsigned char *hashptr = prfhash;
 	struct TCP_Server_Info *server = ses->server;
+	struct hmac_sha256_ctx hmac_ctx;
 
 	memset(prfhash, 0x0, SMB2_HMACSHA256_SIZE);
 	memset(key, 0x0, key_size);
 
 	rc = smb3_crypto_shash_allocate(server);
 	if (rc) {
 		cifs_server_dbg(VFS, "%s: crypto alloc failed\n", __func__);
-		goto smb3signkey_ret;
-	}
-
-	rc = crypto_shash_setkey(server->secmech.hmacsha256->tfm,
-		ses->auth_key.response, SMB2_NTLMV2_SESSKEY_SIZE);
-	if (rc) {
-		cifs_server_dbg(VFS, "%s: Could not set with session key\n", __func__);
-		goto smb3signkey_ret;
-	}
-
-	rc = crypto_shash_init(server->secmech.hmacsha256);
-	if (rc) {
-		cifs_server_dbg(VFS, "%s: Could not init sign hmac\n", __func__);
-		goto smb3signkey_ret;
-	}
-
-	rc = crypto_shash_update(server->secmech.hmacsha256, i, 4);
-	if (rc) {
-		cifs_server_dbg(VFS, "%s: Could not update with n\n", __func__);
-		goto smb3signkey_ret;
-	}
-
-	rc = crypto_shash_update(server->secmech.hmacsha256, label.iov_base, label.iov_len);
-	if (rc) {
-		cifs_server_dbg(VFS, "%s: Could not update with label\n", __func__);
-		goto smb3signkey_ret;
-	}
-
-	rc = crypto_shash_update(server->secmech.hmacsha256, &zero, 1);
-	if (rc) {
-		cifs_server_dbg(VFS, "%s: Could not update with zero\n", __func__);
-		goto smb3signkey_ret;
+		return rc;
 	}
 
-	rc = crypto_shash_update(server->secmech.hmacsha256, context.iov_base, context.iov_len);
-	if (rc) {
-		cifs_server_dbg(VFS, "%s: Could not update with context\n", __func__);
-		goto smb3signkey_ret;
-	}
+	hmac_sha256_init_usingrawkey(&hmac_ctx, ses->auth_key.response,
+				     SMB2_NTLMV2_SESSKEY_SIZE);
+	hmac_sha256_update(&hmac_ctx, i, 4);
+	hmac_sha256_update(&hmac_ctx, label.iov_base, label.iov_len);
+	hmac_sha256_update(&hmac_ctx, &zero, 1);
+	hmac_sha256_update(&hmac_ctx, context.iov_base, context.iov_len);
 
 	if ((server->cipher_type == SMB2_ENCRYPTION_AES256_CCM) ||
 		(server->cipher_type == SMB2_ENCRYPTION_AES256_GCM)) {
-		rc = crypto_shash_update(server->secmech.hmacsha256, L256, 4);
+		hmac_sha256_update(&hmac_ctx, L256, 4);
 	} else {
-		rc = crypto_shash_update(server->secmech.hmacsha256, L128, 4);
-	}
-	if (rc) {
-		cifs_server_dbg(VFS, "%s: Could not update with L\n", __func__);
-		goto smb3signkey_ret;
+		hmac_sha256_update(&hmac_ctx, L128, 4);
 	}
+	hmac_sha256_final(&hmac_ctx, prfhash);
 
-	rc = crypto_shash_final(server->secmech.hmacsha256, hashptr);
-	if (rc) {
-		cifs_server_dbg(VFS, "%s: Could not generate sha256 hash\n", __func__);
-		goto smb3signkey_ret;
-	}
-
-	memcpy(key, hashptr, key_size);
-
-smb3signkey_ret:
-	return rc;
+	memcpy(key, prfhash, key_size);
+	return 0;
 }
 
 struct derivation {
 	struct kvec label;
 	struct kvec context;
-- 
2.51.0