linux-kernel - [PATCH net-next 1/6] mptcp: use HMAC-SHA256 library instead of open-coded HMAC

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Message-Id: <20250901-net-next-mptcp-misc-feat-6-18-v1-1-80ae80d2b903@kernel.org>
Date: Mon, 01 Sep 2025 11:39:10 +0200
From: "Matthieu Baerts (NGI0)" <matttbe@...nel.org>
To: mptcp@...ts.linux.dev, Mat Martineau <martineau@...nel.org>, 
 Geliang Tang <geliang@...nel.org>, "David S. Miller" <davem@...emloft.net>, 
 Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, 
 Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>, 
 Jonathan Corbet <corbet@....net>, Shuah Khan <shuah@...nel.org>
Cc: netdev@...r.kernel.org, linux-kernel@...r.kernel.org, 
 linux-doc@...r.kernel.org, linux-kselftest@...r.kernel.org, 
 "Matthieu Baerts (NGI0)" <matttbe@...nel.org>, 
 Eric Biggers <ebiggers@...nel.org>
Subject: [PATCH net-next 1/6] mptcp: use HMAC-SHA256 library instead of
 open-coded HMAC

From: Eric Biggers <ebiggers@...nel.org>

Now that there are easy-to-use HMAC-SHA256 library functions, use these
in net/mptcp/crypto.c instead of open-coding the HMAC algorithm.

Remove the WARN_ON_ONCE() for messages longer than SHA256_DIGEST_SIZE.
The new implementation handles all message lengths correctly.

The mptcp-crypto KUnit test still passes after this change.

Signed-off-by: Eric Biggers <ebiggers@...nel.org>
Reviewed-by: Matthieu Baerts (NGI0) <matttbe@...nel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@...nel.org>
---
 net/mptcp/crypto.c | 35 ++---------------------------------
 1 file changed, 2 insertions(+), 33 deletions(-)

diff --git a/net/mptcp/crypto.c b/net/mptcp/crypto.c
index b08ba959ac4fd485bb833043ff58d4c8bac8a37a..31948e18d97da7ee0ee2ae9e4f7c9ca0e3b330a7 100644
--- a/net/mptcp/crypto.c
+++ b/net/mptcp/crypto.c
@@ -22,7 +22,6 @@

 #include <linux/kernel.h>
 #include <crypto/sha2.h>
-#include <linux/unaligned.h>

 #include "protocol.h"

@@ -43,39 +42,9 @@ void mptcp_crypto_key_sha(u64 key, u32 *token, u64 *idsn)

 void mptcp_crypto_hmac_sha(u64 key1, u64 key2, u8 *msg, int len, void *hmac)
 {
-	u8 input[SHA256_BLOCK_SIZE + SHA256_DIGEST_SIZE];
-	u8 key1be[8];
-	u8 key2be[8];
-	int i;
+	__be64 key[2] = { cpu_to_be64(key1), cpu_to_be64(key2) };

-	if (WARN_ON_ONCE(len > SHA256_DIGEST_SIZE))
-		len = SHA256_DIGEST_SIZE;
-
-	put_unaligned_be64(key1, key1be);
-	put_unaligned_be64(key2, key2be);
-
-	/* Generate key xored with ipad */
-	memset(input, 0x36, SHA256_BLOCK_SIZE);
-	for (i = 0; i < 8; i++)
-		input[i] ^= key1be[i];
-	for (i = 0; i < 8; i++)
-		input[i + 8] ^= key2be[i];
-
-	memcpy(&input[SHA256_BLOCK_SIZE], msg, len);
-
-	/* emit sha256(K1 || msg) on the second input block, so we can
-	 * reuse 'input' for the last hashing
-	 */
-	sha256(input, SHA256_BLOCK_SIZE + len, &input[SHA256_BLOCK_SIZE]);
-
-	/* Prepare second part of hmac */
-	memset(input, 0x5C, SHA256_BLOCK_SIZE);
-	for (i = 0; i < 8; i++)
-		input[i] ^= key1be[i];
-	for (i = 0; i < 8; i++)
-		input[i + 8] ^= key2be[i];
-
-	sha256(input, SHA256_BLOCK_SIZE + SHA256_DIGEST_SIZE, hmac);
+	hmac_sha256_usingrawkey((const u8 *)key, sizeof(key), msg, len, hmac);
 }

 #if IS_MODULE(CONFIG_MPTCP_KUNIT_TEST)

-- 
2.50.1