From: Johan Hedberg <johan.hedberg@xxxxxxxxx>
Once the public key exchange is complete the next step is for the
non-initiating device to send a SMP Pairing Confirm PDU to the
initiating device. This requires the use of a new smp_f4 confirm value
generation function which in turn builds on the AES-CMAC cryptographic
function.
Signed-off-by: Johan Hedberg <johan.hedberg@xxxxxxxxx>
---
net/bluetooth/smp.c | 96 +++++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 96 insertions(+)
diff --git a/net/bluetooth/smp.c b/net/bluetooth/smp.c
index 1cc438c9c2cb..a1bfcb601c03 100644
--- a/net/bluetooth/smp.c
+++ b/net/bluetooth/smp.c
@@ -43,6 +43,9 @@
0x1f : 0x07)
#define KEY_DIST_MASK 0x07
+/* Maximum message length that can be passed to aes_cmac */
+#define CMAC_MSG_MAX 80
+
enum {
SMP_FLAG_TK_VALID,
SMP_FLAG_CFM_PENDING,
@@ -94,6 +97,84 @@ static inline void swap_buf(const u8 *src, u8 *dst, size_t len)
dst[len - 1 - i] = src[i];
}
+static int aes_cmac(struct crypto_hash *tfm, const u8 k[16], const u8 *m,
+ size_t len, u8 mac[16])
+{
+ uint8_t tmp[16], mac_msb[16], msg_msb[CMAC_MSG_MAX];
+ struct hash_desc desc;
+ struct scatterlist sg;
+ int err;
+
+ if (len > CMAC_MSG_MAX)
+ return -EFBIG;
+
+ if (!tfm) {
+ BT_ERR("tfm %p", tfm);
+ return -EINVAL;
+ }
+
+ desc.tfm = tfm;
+ desc.flags = 0;
+
+ crypto_hash_init(&desc);
+
+ /* Swap key and message from LSB to MSB */
+ swap_buf(k, tmp, 16);
+ swap_buf(m, msg_msb, len);
+
+ BT_DBG("msg (len %zu) %*phN", len, len, m);
+ BT_DBG("key %16phN", k);
+
+ err = crypto_hash_setkey(tfm, tmp, 16);
+ if (err) {
+ BT_ERR("cipher setkey failed: %d", err);
+ return err;
+ }
+
+ sg_init_one(&sg, msg_msb, len);
+
+ err = crypto_hash_update(&desc, &sg, len);
+ if (err) {
+ BT_ERR("Hash update error %d", err);
+ return err;
+ }
+
+ err = crypto_hash_final(&desc, mac_msb);
+ if (err) {
+ BT_ERR("Hash final error %d", err);
+ return err;
+ }
+
+ swap_buf(mac_msb, mac, 16);
+
+ BT_DBG("mac %16phN", mac);
+
+ return 0;
+}
+
+static int smp_f4(struct crypto_hash *tfm_cmac, const u8 u[32], const u8 v[32],
+ const u8 x[16], u8 z, u8 res[16])
+{
+ u8 m[65];
+ int err;
+
+ BT_DBG("u %32phN", u);
+ BT_DBG("v %32phN", v);
+ BT_DBG("x %16phN z %02x", x, z);
+
+ m[0] = z;
+ memcpy(m + 1, v, 32);
+ memcpy(m + 33, u, 32);
+
+ err = aes_cmac(tfm_cmac, x, m, sizeof(m), res);
+ if (err)
+ return err;
+
+ BT_DBG("res %16phN", res);
+
+ return err;
+}
+
static int smp_e(struct crypto_blkcipher *tfm, const u8 *k, u8 *r)
{
struct blkcipher_desc desc;
@@ -1522,6 +1603,7 @@ static int smp_cmd_public_key(struct l2cap_conn *conn, struct sk_buff *skb)
struct hci_conn *hcon = conn->hcon;
struct l2cap_chan *chan = conn->smp;
struct smp_chan *smp = chan->data;
+ struct smp_cmd_pairing_confirm cfm;
int err;
BT_DBG("conn %p", conn);
@@ -1550,6 +1632,20 @@ static int smp_cmd_public_key(struct l2cap_conn *conn, struct sk_buff *skb)
set_bit(SMP_FLAG_REMOTE_PK, &smp->flags);
+ /* The Initiating device waits for the non-initiating device to
+ * send the confirm value.
+ */
+ if (conn->hcon->out)
+ return 0;
+
+ err = smp_f4(smp->tfm_cmac, smp->local_pk, smp->remote_pk, smp->prnd,
+ 0, cfm.confirm_val);
+ if (err)
+ return SMP_UNSPECIFIED;
+
+ smp_send_cmd(conn, SMP_CMD_PAIRING_CONFIRM, sizeof(cfm), &cfm);
+ SMP_ALLOW_CMD(smp, SMP_CMD_PAIRING_RANDOM);
+
return 0;
}
--
2.1.0
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