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authorJohan Hedberg <johan.hedberg@intel.com>2015-03-15 19:34:04 +0200
committerMarcel Holtmann <marcel@holtmann.org>2015-03-17 18:58:24 +0100
commit19c5ce9c5ff80a26cba3afb3684d56539444ee40 (patch)
tree8c298ee5e457c6d23d5d113d23c4e6121035ab0a /net
parentfa4335d71a1408d0112c15874538f3f4e153ba01 (diff)
downloadlinux-19c5ce9c5ff80a26cba3afb3684d56539444ee40.tar.bz2
Bluetooth: Add workaround for broken OS X legacy SMP pairing
OS X version 10.10.2 (and possibly older versions) doesn't support LE Secure Connections but incorrectly copies all authentication request bits from a Security Request to its Pairing Request. The result is that an SC capable initiator (such as BlueZ) will think OS X intends to do SC when in fact it's incapable of it: < ACL Data TX: Handle 3585 flags 0x00 dlen 6 SMP: Security Request (0x0b) len 1 Authentication requirement: Bonding, No MITM, SC, No Keypresses (0x09) > ACL Data RX: Handle 3585 flags 0x02 dlen 11 SMP: Pairing Request (0x01) len 6 IO capability: KeyboardDisplay (0x04) OOB data: Authentication data not present (0x00) Authentication requirement: Bonding, No MITM, SC, No Keypresses (0x09) Max encryption key size: 16 Initiator key distribution: EncKey (0x01) Responder key distribution: EncKey IdKey Sign (0x07) < ACL Data TX: Handle 3585 flags 0x00 dlen 11 SMP: Pairing Response (0x02) len 6 IO capability: NoInputNoOutput (0x03) OOB data: Authentication data not present (0x00) Authentication requirement: Bonding, No MITM, SC, No Keypresses (0x09) Max encryption key size: 16 Initiator key distribution: EncKey (0x01) Responder key distribution: EncKey Sign (0x05) The pairing eventually fails when we get an unexpected Pairing Confirm PDU instead of a Public Key PDU: > ACL Data RX: Handle 3585 flags 0x02 dlen 21 SMP: Pairing Confirm (0x03) len 16 Confim value: bcc3bed31b8f313a78ec3cce32685faf It is only at this point that we can speculate that the remote doesn't really support SC. This patch creates a workaround for the just-works model, however the MITM case is unsolvable because the OS X user has already been requested to enter a PIN which we're now expected to randomly generate and show the user (i.e. a chicken-and-egg problem). Signed-off-by: Johan Hedberg <johan.hedberg@intel.com> Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
Diffstat (limited to 'net')
-rw-r--r--net/bluetooth/smp.c75
1 files changed, 67 insertions, 8 deletions
diff --git a/net/bluetooth/smp.c b/net/bluetooth/smp.c
index 60180b47ce71..6a5afb972358 100644
--- a/net/bluetooth/smp.c
+++ b/net/bluetooth/smp.c
@@ -880,6 +880,12 @@ static int tk_request(struct l2cap_conn *conn, u8 remote_oob, u8 auth,
return 0;
}
+ /* If this function is used for SC -> legacy fallback we
+ * can only recover the just-works case.
+ */
+ if (test_bit(SMP_FLAG_SC, &smp->flags))
+ return -EINVAL;
+
/* Not Just Works/Confirm results in MITM Authentication */
if (smp->method != JUST_CFM) {
set_bit(SMP_FLAG_MITM_AUTH, &smp->flags);
@@ -1806,6 +1812,13 @@ static u8 smp_cmd_pairing_req(struct l2cap_conn *conn, struct sk_buff *skb)
clear_bit(SMP_FLAG_INITIATOR, &smp->flags);
+ /* Strictly speaking we shouldn't allow Pairing Confirm for the
+ * SC case, however some implementations incorrectly copy RFU auth
+ * req bits from our security request, which may create a false
+ * positive SC enablement.
+ */
+ SMP_ALLOW_CMD(smp, SMP_CMD_PAIRING_CONFIRM);
+
if (test_bit(SMP_FLAG_SC, &smp->flags)) {
SMP_ALLOW_CMD(smp, SMP_CMD_PUBLIC_KEY);
/* Clear bits which are generated but not distributed */
@@ -1814,8 +1827,6 @@ static u8 smp_cmd_pairing_req(struct l2cap_conn *conn, struct sk_buff *skb)
return 0;
}
- SMP_ALLOW_CMD(smp, SMP_CMD_PAIRING_CONFIRM);
-
/* Request setup of TK */
ret = tk_request(conn, 0, auth, rsp.io_capability, req->io_capability);
if (ret)
@@ -1981,10 +1992,6 @@ static u8 sc_check_confirm(struct smp_chan *smp)
BT_DBG("");
- /* Public Key exchange must happen before any other steps */
- if (!test_bit(SMP_FLAG_REMOTE_PK, &smp->flags))
- return SMP_UNSPECIFIED;
-
if (smp->method == REQ_PASSKEY || smp->method == DSP_PASSKEY)
return sc_passkey_round(smp, SMP_CMD_PAIRING_CONFIRM);
@@ -1997,6 +2004,47 @@ static u8 sc_check_confirm(struct smp_chan *smp)
return 0;
}
+/* Work-around for some implementations that incorrectly copy RFU bits
+ * from our security request and thereby create the impression that
+ * we're doing SC when in fact the remote doesn't support it.
+ */
+static int fixup_sc_false_positive(struct smp_chan *smp)
+{
+ struct l2cap_conn *conn = smp->conn;
+ struct hci_conn *hcon = conn->hcon;
+ struct hci_dev *hdev = hcon->hdev;
+ struct smp_cmd_pairing *req, *rsp;
+ u8 auth;
+
+ /* The issue is only observed when we're in slave role */
+ if (hcon->out)
+ return SMP_UNSPECIFIED;
+
+ if (hci_dev_test_flag(hdev, HCI_SC_ONLY)) {
+ BT_ERR("Refusing SMP SC -> legacy fallback in SC-only mode");
+ return SMP_UNSPECIFIED;
+ }
+
+ BT_ERR("Trying to fall back to legacy SMP");
+
+ req = (void *) &smp->preq[1];
+ rsp = (void *) &smp->prsp[1];
+
+ /* Rebuild key dist flags which may have been cleared for SC */
+ smp->remote_key_dist = (req->init_key_dist & rsp->resp_key_dist);
+
+ auth = req->auth_req & AUTH_REQ_MASK(hdev);
+
+ if (tk_request(conn, 0, auth, rsp->io_capability, req->io_capability)) {
+ BT_ERR("Failed to fall back to legacy SMP");
+ return SMP_UNSPECIFIED;
+ }
+
+ clear_bit(SMP_FLAG_SC, &smp->flags);
+
+ return 0;
+}
+
static u8 smp_cmd_pairing_confirm(struct l2cap_conn *conn, struct sk_buff *skb)
{
struct l2cap_chan *chan = conn->smp;
@@ -2010,8 +2058,19 @@ static u8 smp_cmd_pairing_confirm(struct l2cap_conn *conn, struct sk_buff *skb)
memcpy(smp->pcnf, skb->data, sizeof(smp->pcnf));
skb_pull(skb, sizeof(smp->pcnf));
- if (test_bit(SMP_FLAG_SC, &smp->flags))
- return sc_check_confirm(smp);
+ if (test_bit(SMP_FLAG_SC, &smp->flags)) {
+ int ret;
+
+ /* Public Key exchange must happen before any other steps */
+ if (test_bit(SMP_FLAG_REMOTE_PK, &smp->flags))
+ return sc_check_confirm(smp);
+
+ BT_ERR("Unexpected SMP Pairing Confirm");
+
+ ret = fixup_sc_false_positive(smp);
+ if (ret)
+ return ret;
+ }
if (conn->hcon->out) {
smp_send_cmd(conn, SMP_CMD_PAIRING_RANDOM, sizeof(smp->prnd),