Bluetooth: Add MITM mechanism to LE-SMP

To achive Man-In-The-Middle (MITM) level security with Low Energy,
we have to enable User Passkey Comparison.  This commit modifies the
hard-coded JUST-WORKS pairing mechanism to support query via the MGMT
interface of Passkey comparison and User Confirmation.

Signed-off-by: Brian Gix <bgix@codeaurora.org>
Acked-by: Marcel Holtmann<marcel@holtmann.org>
Signed-off-by: Gustavo F. Padovan <padovan@profusion.mobi>

1 files changed, 204 insertions, 22 deletions

diff --git a/net/bluetooth/smp.c b/net/bluetooth/smp.c
index 0ee2905a6179..9fea4bfd0eb5 100644
--- a/net/bluetooth/smp.c
+++ b/net/bluetooth/smp.c
@@ -23,6 +23,7 @@
 #include <net/bluetooth/bluetooth.h>
 #include <net/bluetooth/hci_core.h>
 #include <net/bluetooth/l2cap.h>
+#include <net/bluetooth/mgmt.h>
 #include <net/bluetooth/smp.h>
 #include <linux/crypto.h>
 #include <linux/scatterlist.h>
@@ -189,24 +190,45 @@ static void smp_send_cmd(struct l2cap_conn *conn, u8 code, u16 len, void *data)
                                         msecs_to_jiffies(SMP_TIMEOUT));
 }
 
+static __u8 authreq_to_seclevel(__u8 authreq)
+{
+        if (authreq & SMP_AUTH_MITM)
+                return BT_SECURITY_HIGH;
+        else
+                return BT_SECURITY_MEDIUM;
+}
+
+static __u8 seclevel_to_authreq(__u8 sec_level)
+{
+        switch (sec_level) {
+        case BT_SECURITY_HIGH:
+                return SMP_AUTH_MITM | SMP_AUTH_BONDING;
+        case BT_SECURITY_MEDIUM:
+                return SMP_AUTH_BONDING;
+        default:
+                return SMP_AUTH_NONE;
+        }
+}
+
 static void build_pairing_cmd(struct l2cap_conn *conn,
                                 struct smp_cmd_pairing *req,
                                 struct smp_cmd_pairing *rsp,
                                 __u8 authreq)
 {
-        u8 dist_keys;
+        u8 dist_keys = 0;
 
-        dist_keys = 0;
         if (test_bit(HCI_PAIRABLE, &conn->hcon->hdev->flags)) {
                 dist_keys = SMP_DIST_ENC_KEY;
                 authreq |= SMP_AUTH_BONDING;
+        } else {
+                authreq &= ~SMP_AUTH_BONDING;
         }
 
         if (rsp == NULL) {
                 req->io_capability = conn->hcon->io_capability;
                 req->oob_flag = SMP_OOB_NOT_PRESENT;
                 req->max_key_size = SMP_MAX_ENC_KEY_SIZE;
-                req->init_key_dist = dist_keys;
+                req->init_key_dist = 0;
                 req->resp_key_dist = dist_keys;
                 req->auth_req = authreq;
                 return;
@@ -215,7 +237,7 @@ static void build_pairing_cmd(struct l2cap_conn *conn,
         rsp->io_capability = conn->hcon->io_capability;
         rsp->oob_flag = SMP_OOB_NOT_PRESENT;
         rsp->max_key_size = SMP_MAX_ENC_KEY_SIZE;
-        rsp->init_key_dist = req->init_key_dist & dist_keys;
+        rsp->init_key_dist = 0;
         rsp->resp_key_dist = req->resp_key_dist & dist_keys;
         rsp->auth_req = authreq;
 }
@@ -245,6 +267,95 @@ static void smp_failure(struct l2cap_conn *conn, u8 reason, u8 send)
         smp_chan_destroy(conn);
 }
 
+#define JUST_WORKS      0x00
+#define JUST_CFM        0x01
+#define REQ_PASSKEY     0x02
+#define CFM_PASSKEY     0x03
+#define REQ_OOB         0x04
+#define OVERLAP         0xFF
+
+static const u8 gen_method[5][5] = {
+        { JUST_WORKS,  JUST_CFM,    REQ_PASSKEY, JUST_WORKS, REQ_PASSKEY },
+        { JUST_WORKS,  JUST_CFM,    REQ_PASSKEY, JUST_WORKS, REQ_PASSKEY },
+        { CFM_PASSKEY, CFM_PASSKEY, REQ_PASSKEY, JUST_WORKS, CFM_PASSKEY },
+        { JUST_WORKS,  JUST_CFM,    JUST_WORKS,  JUST_WORKS, JUST_CFM    },
+        { CFM_PASSKEY, CFM_PASSKEY, REQ_PASSKEY, JUST_WORKS, OVERLAP     },
+};
+
+static int tk_request(struct l2cap_conn *conn, u8 remote_oob, u8 auth,
+                                                u8 local_io, u8 remote_io)
+{
+        struct hci_conn *hcon = conn->hcon;
+        struct smp_chan *smp = conn->smp_chan;
+        u8 method;
+        u32 passkey = 0;
+        int ret = 0;
+
+        /* Initialize key for JUST WORKS */
+        memset(smp->tk, 0, sizeof(smp->tk));
+        clear_bit(SMP_FLAG_TK_VALID, &smp->smp_flags);
+
+        BT_DBG("tk_request: auth:%d lcl:%d rem:%d", auth, local_io, remote_io);
+
+        /* If neither side wants MITM, use JUST WORKS */
+        /* If either side has unknown io_caps, use JUST WORKS */
+        /* Otherwise, look up method from the table */
+        if (!(auth & SMP_AUTH_MITM) ||
+                        local_io > SMP_IO_KEYBOARD_DISPLAY ||
+                        remote_io > SMP_IO_KEYBOARD_DISPLAY)
+                method = JUST_WORKS;
+        else
+                method = gen_method[local_io][remote_io];
+
+        /* If not bonding, don't ask user to confirm a Zero TK */
+        if (!(auth & SMP_AUTH_BONDING) && method == JUST_CFM)
+                method = JUST_WORKS;
+
+        /* If Just Works, Continue with Zero TK */
+        if (method == JUST_WORKS) {
+                set_bit(SMP_FLAG_TK_VALID, &smp->smp_flags);
+                return 0;
+        }
+
+        /* Not Just Works/Confirm results in MITM Authentication */
+        if (method != JUST_CFM)
+                set_bit(SMP_FLAG_MITM_AUTH, &smp->smp_flags);
+
+        /* If both devices have Keyoard-Display I/O, the master
+         * Confirms and the slave Enters the passkey.
+         */
+        if (method == OVERLAP) {
+                if (hcon->link_mode & HCI_LM_MASTER)
+                        method = CFM_PASSKEY;
+                else
+                        method = REQ_PASSKEY;
+        }
+
+        /* Generate random passkey. Not valid until confirmed. */
+        if (method == CFM_PASSKEY) {
+                u8 key[16];
+
+                memset(key, 0, sizeof(key));
+                get_random_bytes(&passkey, sizeof(passkey));
+                passkey %= 1000000;
+                put_unaligned_le32(passkey, key);
+                swap128(key, smp->tk);
+                BT_DBG("PassKey: %d", passkey);
+        }
+
+        hci_dev_lock(hcon->hdev);
+
+        if (method == REQ_PASSKEY)
+                ret = mgmt_user_passkey_request(hcon->hdev, conn->dst);
+        else
+                ret = mgmt_user_confirm_request(hcon->hdev, conn->dst,
+                                                cpu_to_le32(passkey), 0);
+
+        hci_dev_unlock(hcon->hdev);
+
+        return ret;
+}
+
 static void confirm_work(struct work_struct *work)
 {
         struct smp_chan *smp = container_of(work, struct smp_chan, confirm);
@@ -277,6 +388,8 @@ static void confirm_work(struct work_struct *work)
                 goto error;
         }
 
+        clear_bit(SMP_FLAG_CFM_PENDING, &smp->smp_flags);
+
         swap128(res, cp.confirm_val);
         smp_send_cmd(smp->conn, SMP_CMD_PAIRING_CONFIRM, sizeof(cp), &cp);
 
@@ -382,6 +495,7 @@ static struct smp_chan *smp_chan_create(struct l2cap_conn *conn)
 
         smp->conn = conn;
         conn->smp_chan = smp;
+        conn->hcon->smp_conn = conn;
 
         hci_conn_hold(conn->hcon);
 
@@ -399,18 +513,64 @@ void smp_chan_destroy(struct l2cap_conn *conn)
 
         kfree(smp);
         conn->smp_chan = NULL;
+        conn->hcon->smp_conn = NULL;
         hci_conn_put(conn->hcon);
 }
 
+int smp_user_confirm_reply(struct hci_conn *hcon, u16 mgmt_op, __le32 passkey)
+{
+        struct l2cap_conn *conn = hcon->smp_conn;
+        struct smp_chan *smp;
+        u32 value;
+        u8 key[16];
+
+        BT_DBG("");
+
+        if (!conn)
+                return -ENOTCONN;
+
+        smp = conn->smp_chan;
+
+        switch (mgmt_op) {
+        case MGMT_OP_USER_PASSKEY_REPLY:
+                value = le32_to_cpu(passkey);
+                memset(key, 0, sizeof(key));
+                BT_DBG("PassKey: %d", value);
+                put_unaligned_le32(value, key);
+                swap128(key, smp->tk);
+                /* Fall Through */
+        case MGMT_OP_USER_CONFIRM_REPLY:
+                set_bit(SMP_FLAG_TK_VALID, &smp->smp_flags);
+                break;
+        case MGMT_OP_USER_PASSKEY_NEG_REPLY:
+        case MGMT_OP_USER_CONFIRM_NEG_REPLY:
+                smp_failure(conn, SMP_PASSKEY_ENTRY_FAILED, 1);
+                return 0;
+        default:
+                smp_failure(conn, SMP_PASSKEY_ENTRY_FAILED, 1);
+                return -EOPNOTSUPP;
+        }
+
+        /* If it is our turn to send Pairing Confirm, do so now */
+        if (test_bit(SMP_FLAG_CFM_PENDING, &smp->smp_flags))
+                queue_work(hcon->hdev->workqueue, &smp->confirm);
+
+        return 0;
+}
+
 static u8 smp_cmd_pairing_req(struct l2cap_conn *conn, struct sk_buff *skb)
 {
         struct smp_cmd_pairing rsp, *req = (void *) skb->data;
         struct smp_chan *smp;
         u8 key_size;
+        u8 auth = SMP_AUTH_NONE;
         int ret;
 
         BT_DBG("conn %p", conn);
 
+        if (conn->hcon->link_mode & HCI_LM_MASTER)
+                return SMP_CMD_NOTSUPP;
+
         if (!test_and_set_bit(HCI_CONN_LE_SMP_PEND, &conn->hcon->pend))
                 smp = smp_chan_create(conn);
 
@@ -420,19 +580,16 @@ static u8 smp_cmd_pairing_req(struct l2cap_conn *conn, struct sk_buff *skb)
         memcpy(&smp->preq[1], req, sizeof(*req));
         skb_pull(skb, sizeof(*req));
 
-        if (req->oob_flag)
-                return SMP_OOB_NOT_AVAIL;
+        /* We didn't start the pairing, so match remote */
+        if (req->auth_req & SMP_AUTH_BONDING)
+                auth = req->auth_req;
 
-        /* We didn't start the pairing, so no requirements */
-        build_pairing_cmd(conn, req, &rsp, SMP_AUTH_NONE);
+        build_pairing_cmd(conn, req, &rsp, auth);
 
         key_size = min(req->max_key_size, rsp.max_key_size);
         if (check_enc_key_size(conn, key_size))
                 return SMP_ENC_KEY_SIZE;
 
-        /* Just works */
-        memset(smp->tk, 0, sizeof(smp->tk));
-
         ret = smp_rand(smp->prnd);
         if (ret)
                 return SMP_UNSPECIFIED;
@@ -442,6 +599,11 @@ static u8 smp_cmd_pairing_req(struct l2cap_conn *conn, struct sk_buff *skb)
 
         smp_send_cmd(conn, SMP_CMD_PAIRING_RSP, sizeof(rsp), &rsp);
 
+        /* Request setup of TK */
+        ret = tk_request(conn, 0, auth, rsp.io_capability, req->io_capability);
+        if (ret)
+                return SMP_UNSPECIFIED;
+
         return 0;
 }
 
@@ -450,11 +612,14 @@ static u8 smp_cmd_pairing_rsp(struct l2cap_conn *conn, struct sk_buff *skb)
         struct smp_cmd_pairing *req, *rsp = (void *) skb->data;
         struct smp_chan *smp = conn->smp_chan;
         struct hci_dev *hdev = conn->hcon->hdev;
-        u8 key_size;
+        u8 key_size, auth = SMP_AUTH_NONE;
         int ret;
 
         BT_DBG("conn %p", conn);
 
+        if (!(conn->hcon->link_mode & HCI_LM_MASTER))
+                return SMP_CMD_NOTSUPP;
+
         skb_pull(skb, sizeof(*rsp));
 
         req = (void *) &smp->preq[1];
@@ -463,12 +628,6 @@ static u8 smp_cmd_pairing_rsp(struct l2cap_conn *conn, struct sk_buff *skb)
         if (check_enc_key_size(conn, key_size))
                 return SMP_ENC_KEY_SIZE;
 
-        if (rsp->oob_flag)
-                return SMP_OOB_NOT_AVAIL;
-
-        /* Just works */
-        memset(smp->tk, 0, sizeof(smp->tk));
-
         ret = smp_rand(smp->prnd);
         if (ret)
                 return SMP_UNSPECIFIED;
@@ -476,6 +635,22 @@ static u8 smp_cmd_pairing_rsp(struct l2cap_conn *conn, struct sk_buff *skb)
         smp->prsp[0] = SMP_CMD_PAIRING_RSP;
         memcpy(&smp->prsp[1], rsp, sizeof(*rsp));
 
+        if ((req->auth_req & SMP_AUTH_BONDING) &&
+                        (rsp->auth_req & SMP_AUTH_BONDING))
+                auth = SMP_AUTH_BONDING;
+
+        auth |= (req->auth_req | rsp->auth_req) & SMP_AUTH_MITM;
+
+        ret = tk_request(conn, 0, auth, rsp->io_capability, req->io_capability);
+        if (ret)
+                return SMP_UNSPECIFIED;
+
+        set_bit(SMP_FLAG_CFM_PENDING, &smp->smp_flags);
+
+        /* Can't compose response until we have been confirmed */
+        if (!test_bit(SMP_FLAG_TK_VALID, &smp->smp_flags))
+                return 0;
+
         queue_work(hdev->workqueue, &smp->confirm);
 
         return 0;
@@ -497,8 +672,10 @@ static u8 smp_cmd_pairing_confirm(struct l2cap_conn *conn, struct sk_buff *skb)
                 swap128(smp->prnd, random);
                 smp_send_cmd(conn, SMP_CMD_PAIRING_RANDOM, sizeof(random),
                                                                 random);
-        } else {
+        } else if (test_bit(SMP_FLAG_TK_VALID, &smp->smp_flags)) {
                 queue_work(hdev->workqueue, &smp->confirm);
+        } else {
+                set_bit(SMP_FLAG_CFM_PENDING, &smp->smp_flags);
         }
 
         return 0;
@@ -551,7 +728,7 @@ static u8 smp_cmd_security_req(struct l2cap_conn *conn, struct sk_buff *skb)
 
         BT_DBG("conn %p", conn);
 
-        hcon->pending_sec_level = BT_SECURITY_MEDIUM;
+        hcon->pending_sec_level = authreq_to_seclevel(rp->auth_req);
 
         if (smp_ltk_encrypt(conn))
                 return 0;
@@ -578,6 +755,7 @@ int smp_conn_security(struct l2cap_conn *conn, __u8 sec_level)
 {
         struct hci_conn *hcon = conn->hcon;
         struct smp_chan *smp = conn->smp_chan;
+        __u8 authreq;
 
         BT_DBG("conn %p hcon %p level 0x%2.2x", conn, hcon, sec_level);
 
@@ -598,18 +776,22 @@ int smp_conn_security(struct l2cap_conn *conn, __u8 sec_level)
                 return 0;
 
         smp = smp_chan_create(conn);
+        if (!smp)
+                return 1;
+
+        authreq = seclevel_to_authreq(sec_level);
 
         if (hcon->link_mode & HCI_LM_MASTER) {
                 struct smp_cmd_pairing cp;
 
-                build_pairing_cmd(conn, &cp, NULL, SMP_AUTH_NONE);
+                build_pairing_cmd(conn, &cp, NULL, authreq);
                 smp->preq[0] = SMP_CMD_PAIRING_REQ;
                 memcpy(&smp->preq[1], &cp, sizeof(cp));
 
                 smp_send_cmd(conn, SMP_CMD_PAIRING_REQ, sizeof(cp), &cp);
         } else {
                 struct smp_cmd_security_req cp;
-                cp.auth_req = SMP_AUTH_NONE;
+                cp.auth_req = authreq;
                 smp_send_cmd(conn, SMP_CMD_SECURITY_REQ, sizeof(cp), &cp);
         }