[PATCH BlueZ v2 1/3] src: add HMAC-SHA256 to bt_crypto using kernel AF_ALG

From: Pakrohk <[email protected]>

Add HMAC-SHA256 computation to the bt_crypto library using the Linux
kernel AF_ALG interface. This follows the exact same pattern as the
existing cmac(aes) implementation.

The HMAC-SHA256 function is needed for verifying external quirk profile
signatures. The previous implementation used popen("openssl dgst ...")
which had command injection risks and an openssl CLI dependency.

Using kernel AF_ALG:
  - No external library dependencies
  - Matches existing BlueZ crypto patterns
  - No shell invocation or temp files
  - Works in bluetoothd's process context

The hmac(sha256) algorithm is available in all modern Linux kernels
via the crypto API (/proc/crypto).

Signed-off-by: Pakrohk <[email protected]>
diff --git a/src/shared/crypto.c b/src/shared/crypto.c
index cb99116..f5883bd 100644
--- a/src/shared/crypto.c
+++ b/src/shared/crypto.c
@@ -69,6 +69,7 @@ struct bt_crypto {
 	int ecb_aes;
 	int urandom;
 	int cmac_aes;
+	int hmac_sha256;
 };
 
 static int urandom_setup(void)
@@ -126,6 +127,28 @@ static int cmac_aes_setup(void)
 	return fd;
 }
 
+static int hmac_sha256_setup(void)
+{
+	struct sockaddr_alg salg;
+	int fd;
+
+	fd = socket(PF_ALG, SOCK_SEQPACKET | SOCK_CLOEXEC, 0);
+	if (fd < 0)
+		return -1;
+
+	memset(&salg, 0, sizeof(salg));
+	salg.salg_family = AF_ALG;
+	strcpy((char *) salg.salg_type, "hash");
+	strcpy((char *) salg.salg_name, "hmac(sha256)");
+
+	if (bind(fd, (struct sockaddr *) &salg, sizeof(salg)) < 0) {
+		close(fd);
+		return -1;
+	}
+
+	return fd;
+}
+
 static struct bt_crypto *singleton;
 
 struct bt_crypto *bt_crypto_new(void)
@@ -159,6 +182,16 @@ struct bt_crypto *bt_crypto_new(void)
 		return NULL;
 	}
 
+	singleton->hmac_sha256 = hmac_sha256_setup();
+	if (singleton->hmac_sha256 < 0) {
+		close(singleton->cmac_aes);
+		close(singleton->urandom);
+		close(singleton->ecb_aes);
+		free(singleton);
+		singleton = NULL;
+		return NULL;
+	}
+
 	return bt_crypto_ref(singleton);
 }
 
@@ -183,6 +216,7 @@ void bt_crypto_unref(struct bt_crypto *crypto)
 	close(crypto->urandom);
 	close(crypto->ecb_aes);
 	close(crypto->cmac_aes);
+	close(crypto->hmac_sha256);
 
 	free(crypto);
 	singleton = NULL;
@@ -1005,3 +1039,35 @@ bool bt_crypto_sirk(struct bt_crypto *crypto, const char *str, uint16_t vendor,
 	/* Encrypt sirk using k as LTK with sef function */
 	return bt_crypto_sef(crypto, k, sirk_plaintext, sirk);
 }
+
+bool bt_crypto_hmac_sha256(struct bt_crypto *crypto,
+				const uint8_t *key, size_t key_len,
+				const uint8_t *msg, size_t msg_len,
+				uint8_t res[32])
+{
+	ssize_t len;
+	int fd;
+
+	if (!crypto)
+		return false;
+
+	fd = alg_new(crypto->hmac_sha256, key, key_len);
+	if (fd < 0)
+		return false;
+
+	len = send(fd, msg, msg_len, 0);
+	if (len < 0) {
+		close(fd);
+		return false;
+	}
+
+	len = read(fd, res, 32);
+	if (len < 0) {
+		close(fd);
+		return false;
+	}
+
+	close(fd);
+
+	return true;
+}
diff --git a/src/shared/crypto.h b/src/shared/crypto.h
index d85f807..6b234bc 100644
--- a/src/shared/crypto.h
+++ b/src/shared/crypto.h
@@ -62,3 +62,8 @@ bool bt_crypto_sirk(struct bt_crypto *crypto, const char *str, uint16_t vendor,
 			uint8_t sirk[16]);
 bool bt_crypto_rsi(struct bt_crypto *crypto, const uint8_t sirk[16],
 					uint8_t rsi[6]);
+
+bool bt_crypto_hmac_sha256(struct bt_crypto *crypto,
+				const uint8_t *key, size_t key_len,
+				const uint8_t *msg, size_t msg_len,
+				uint8_t res[32]);