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Date:   Mon,  6 Apr 2020 19:48:43 +0800
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Subject: [Bluez PATCH v3 1/3] shared/crypto: Add bt_crypto_verify_att_sign
From:   Archie Pusaka <apusaka@google.com>
To:     linux-bluetooth <linux-bluetooth@vger.kernel.org>,
        Luiz Augusto von Dentz <luiz.dentz@gmail.com>
Cc:     Archie Pusaka <apusaka@chromium.org>
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From: Archie Pusaka <apusaka@chromium.org>

This is used to verify the signature of incoming ATT packets.

---

Changes in v3:
- Add check for the case where pdu_len < ATT_SIGN_LEN

Changes in v2: None

 src/shared/crypto.c | 28 ++++++++++++++++++++++++++--
 src/shared/crypto.h |  2 ++
 2 files changed, 28 insertions(+), 2 deletions(-)

diff --git a/src/shared/crypto.c b/src/shared/crypto.c
index 5c5e1217d..5cc88ce4a 100644
--- a/src/shared/crypto.c
+++ b/src/shared/crypto.c
@@ -75,6 +75,8 @@ struct af_alg_iv {
 /* Maximum message length that can be passed to aes_cmac */
 #define CMAC_MSG_MAX	80
 
+#define ATT_SIGN_LEN	12
+
 struct bt_crypto {
 	int ref_count;
 	int ecb_aes;
@@ -265,7 +267,8 @@ static inline void swap_buf(const uint8_t *src, uint8_t *dst, uint16_t len)
 
 bool bt_crypto_sign_att(struct bt_crypto *crypto, const uint8_t key[16],
 				const uint8_t *m, uint16_t m_len,
-				uint32_t sign_cnt, uint8_t signature[12])
+				uint32_t sign_cnt,
+				uint8_t signature[ATT_SIGN_LEN])
 {
 	int fd;
 	int len;
@@ -319,10 +322,31 @@ bool bt_crypto_sign_att(struct bt_crypto *crypto, const uint8_t key[16],
 	 * 12 octets
 	 */
 	swap_buf(out, tmp, 16);
-	memcpy(signature, tmp + 4, 12);
+	memcpy(signature, tmp + 4, ATT_SIGN_LEN);
 
 	return true;
 }
+
+bool bt_crypto_verify_att_sign(struct bt_crypto *crypto, const uint8_t key[16],
+				const uint8_t *pdu, uint16_t pdu_len)
+{
+	uint8_t generated_sign[ATT_SIGN_LEN];
+	const uint8_t *sign;
+	uint32_t sign_cnt;
+
+	if (pdu_len < ATT_SIGN_LEN)
+		return false;
+
+	sign = pdu + pdu_len - ATT_SIGN_LEN;
+	sign_cnt = get_le32(sign);
+
+	if (!bt_crypto_sign_att(crypto, key, pdu, pdu_len - ATT_SIGN_LEN,
+						sign_cnt, generated_sign))
+		return false;
+
+	return memcmp(generated_sign, sign, ATT_SIGN_LEN) == 0;
+}
+
 /*
  * Security function e
  *
diff --git a/src/shared/crypto.h b/src/shared/crypto.h
index c58d2e104..d17daa835 100644
--- a/src/shared/crypto.h
+++ b/src/shared/crypto.h
@@ -62,5 +62,7 @@ bool bt_crypto_h6(struct bt_crypto *crypto, const uint8_t w[16],
 bool bt_crypto_sign_att(struct bt_crypto *crypto, const uint8_t key[16],
 				const uint8_t *m, uint16_t m_len,
 				uint32_t sign_cnt, uint8_t signature[12]);
+bool bt_crypto_verify_att_sign(struct bt_crypto *crypto, const uint8_t key[16],
+				const uint8_t *pdu, uint16_t pdu_len);
 bool bt_crypto_gatt_hash(struct bt_crypto *crypto, struct iovec *iov,
 				size_t iov_len, uint8_t res[16]);
-- 
2.26.0.292.g33ef6b2f38-goog