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Thu, 05 Nov 2026 09:12:25 -0800 (PST) Received: from lvondent-mobl5.taila91cb8.ts.net ([72.188.211.115]) by smtp.gmail.com with ESMTPSA id 71dfb90a1353d-5eca8d9d62bsm4551846e0c.8.2026.11.05.09.12.24 for (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 05 Nov 2026 09:12:24 -0800 (PST) From: Luiz Augusto von Dentz To: linux-bluetooth@vger.kernel.org Subject: [PATCH v4 4/6] Bluetooth: L2CAP: Add MIC length validation for HDT PHY Date: Thu, 5 Nov 2026 12:12:15 -0500 Message-ID: <20261105171217.2053745-5-luiz.dentz@gmail.com> X-Mailer: git-send-email 2.56.0 In-Reply-To: <20261105171217.2053745-1-luiz.dentz@gmail.com> References: <20261105171217.2053745-1-luiz.dentz@gmail.com> X-Mailing-List: linux-bluetooth@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Luiz Augusto von Dentz Add a mic_len field to struct bt_security so userspace can require a minimum MIC length on an L2CAP channel with BT_SECURITY, and read the MIC length in use on the link back. The field is added at the end of the struct, so the shorter struct is still accepted by L2CAP and RFCOMM, leaving mic_len unset, and values other than 32, 64 and 128 bits are rejected. The MIC length a channel requires is requested on the connection on every path starting LE security, so LE Enable Encryption v2 asks for it, while the MIC length the controller reports with Encryption Change v3 and Encryption Key Refresh Complete v2 is kept separately, so a request never stands for what is in use. When a connection is encrypted on the LE HDT PHY with a MIC shorter than the channel requires, the LE Credit Based and Enhanced Credit Based connection requests are rejected with MIC Length Too Short. The reported MIC length only applies on the LE HDT PHY, the MIC is always 32 bits on the GFSK PHYs, so hci_conn_mic_len() reports it as such both for the check and for BT_SECURITY. Signed-off-by: Luiz Augusto von Dentz --- include/net/bluetooth/bluetooth.h | 1 + include/net/bluetooth/hci_core.h | 9 +++++++ include/net/bluetooth/l2cap.h | 7 +++++ net/bluetooth/hci_event.c | 19 ++++++++++--- net/bluetooth/hci_sync.c | 5 +++- net/bluetooth/l2cap_core.c | 44 ++++++++++++++++++++++++++++++- net/bluetooth/l2cap_sock.c | 23 +++++++++++++--- net/bluetooth/rfcomm/sock.c | 13 ++++++--- 8 files changed, 110 insertions(+), 11 deletions(-) diff --git a/include/net/bluetooth/bluetooth.h b/include/net/bluetooth/bluetooth.h index d59407349b3e..777bc1a0336b 100644 --- a/include/net/bluetooth/bluetooth.h +++ b/include/net/bluetooth/bluetooth.h @@ -66,6 +66,7 @@ struct bt_security { __u8 level; __u8 key_size; + __u8 mic_len; }; #define BT_SECURITY_SDP 0 #define BT_SECURITY_LOW 1 diff --git a/include/net/bluetooth/hci_core.h b/include/net/bluetooth/hci_core.h index 7a4f87236854..fb4f6735f69b 100644 --- a/include/net/bluetooth/hci_core.h +++ b/include/net/bluetooth/hci_core.h @@ -765,6 +765,8 @@ struct hci_conn { __u8 pending_sec_level; __u8 pin_length; __u8 enc_key_size; + __u8 mic_len; + __u8 req_mic_len; __u8 io_capability; __u32 passkey_notify; __u8 passkey_entered; @@ -2178,6 +2180,13 @@ void hci_conn_del_sysfs(struct hci_conn *conn); (le_feature(dev, 1, 2) & HCI_LE_HDT_7_5_TX_FEATURE) #define hdt_pf1_capable(dev) \ (le_feature(dev, 1, 2) & HCI_LE_HDT_PF_1) +/* The MIC length reported by the controller only applies on the LE HDT PHY, + * the MIC is always 32 bits (0x00) on the GFSK PHYs. + */ +static inline __u8 hci_conn_mic_len(struct hci_conn *conn) +{ + return conn->le_rx_phy == 0x05 ? conn->mic_len : 0x00; +} #define eks_capable(dev) \ (le_feature(dev, 1, 1) & HCI_LE_EKS_FEATURE) diff --git a/include/net/bluetooth/l2cap.h b/include/net/bluetooth/l2cap.h index 54eddcdd341f..7eda42071b06 100644 --- a/include/net/bluetooth/l2cap.h +++ b/include/net/bluetooth/l2cap.h @@ -285,6 +285,11 @@ struct l2cap_conn_rsp { #define L2CAP_CR_LE_SCID_IN_USE 0x000A #define L2CAP_CR_LE_UNACCEPT_PARAMS 0x000B #define L2CAP_CR_LE_INVALID_PARAMS 0x000C +/* MIC Length Too Short has a different value in each response: the LE Credit + * Based value is Invalid Parameters in the Enhanced Credit Based one. + */ +#define L2CAP_CR_LE_MIC_LEN_TOO_SHORT 0x000C +#define L2CAP_CR_ECRED_MIC_LEN_TOO_SHORT 0x0010 /* connect/create channel status */ #define L2CAP_CS_NO_INFO 0x0000 @@ -533,6 +538,7 @@ struct l2cap_chan { __u8 chan_policy; __u8 sec_level; + __u8 mic_len; __u8 ident; @@ -981,6 +987,7 @@ int l2cap_chan_send(struct l2cap_chan *chan, struct msghdr *msg, size_t len, const struct sockcm_cookie *sockc); void l2cap_chan_busy(struct l2cap_chan *chan, int busy); void l2cap_chan_rx_avail(struct l2cap_chan *chan, ssize_t rx_avail); +void l2cap_chan_req_mic_len(struct l2cap_chan *chan, struct hci_conn *hcon); int l2cap_chan_check_security(struct l2cap_chan *chan, bool initiator); void l2cap_chan_set_defaults(struct l2cap_chan *chan, struct l2cap_chan *pchan); int l2cap_ertm_init(struct l2cap_chan *chan); diff --git a/net/bluetooth/hci_event.c b/net/bluetooth/hci_event.c index fb30615db02a..e826809f8c75 100644 --- a/net/bluetooth/hci_event.c +++ b/net/bluetooth/hci_event.c @@ -3760,7 +3760,8 @@ static void hci_remote_name_evt(struct hci_dev *hdev, void *data, hci_dev_unlock(hdev); } -static void hci_change_encrypt(struct hci_conn *conn, u8 status, u8 encrypt) +static void hci_change_encrypt(struct hci_conn *conn, u8 status, u8 encrypt, + u8 mic_len) { struct hci_dev *hdev = conn->hdev; @@ -3779,6 +3780,14 @@ static void hci_change_encrypt(struct hci_conn *conn, u8 status, u8 encrypt) conn->type == LE_LINK) set_bit(HCI_CONN_AES_CCM, conn->flags); + /* The key size of Encryption Change v3 is not used: + * it is ignored for LE, where it comes from SMP, and + * the ACL key size is read below. + * + * A 32-bit MIC is reported as 0x00. + */ + conn->mic_len = mic_len; + /* For ACL links the encryption key size is still * validated below via hci_read_enc_key_size(). Its * completion handler, hci_cc_read_enc_key_size(), @@ -3888,7 +3897,7 @@ static void hci_encrypt_change_evt(struct hci_dev *hdev, void *data, if (!conn) goto unlock; - hci_change_encrypt(conn, ev->status, ev->encrypt); + hci_change_encrypt(conn, ev->status, ev->encrypt, 0); unlock: hci_dev_unlock(hdev); @@ -3908,7 +3917,7 @@ static void hci_encrypt_change_v3_evt(struct hci_dev *hdev, void *data, if (!conn) goto unlock; - hci_change_encrypt(conn, ev->status, ev->mode); + hci_change_encrypt(conn, ev->status, ev->mode, ev->mic_len); unlock: hci_dev_unlock(hdev); @@ -5694,6 +5703,10 @@ static void hci_key_refresh_complete_v2_evt(struct hci_dev *hdev, void *data, if (!conn) goto unlock; + /* The key refresh may change the MIC length */ + if (!ev->status) + conn->mic_len = ev->mic_len; + hci_conn_refresh_key(conn, ev->status); unlock: diff --git a/net/bluetooth/hci_sync.c b/net/bluetooth/hci_sync.c index c2929fdd2ad2..19ebbcb9f6af 100644 --- a/net/bluetooth/hci_sync.c +++ b/net/bluetooth/hci_sync.c @@ -8644,7 +8644,10 @@ static int hci_le_enable_encrypt_v2(struct hci_conn *conn, __le16 ediv, cp->handle = cpu_to_le16(conn->handle); cp->rand = rand; cp->ediv = ediv; - cp->mic_len = 0x02; /* Always prefer 128 bits? */ + /* Use the MIC length requested for the connection, default to 128 + * bits if unset. + */ + cp->mic_len = conn->req_mic_len ? conn->req_mic_len : 0x02; /* The key is zero padded when shorter than 16 octets */ if (ltk) { diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c index 70ad30b091e4..b19dd027adc3 100644 --- a/net/bluetooth/l2cap_core.c +++ b/net/bluetooth/l2cap_core.c @@ -579,6 +579,7 @@ void l2cap_chan_set_defaults(struct l2cap_chan *chan, struct l2cap_chan *pchan) chan->tx_win = pchan->tx_win; chan->tx_win_max = pchan->tx_win_max; chan->sec_level = pchan->sec_level; + chan->mic_len = pchan->mic_len; chan->conf_state = pchan->conf_state; chan->flags = pchan->flags; chan->tx_credits = pchan->tx_credits; @@ -1025,14 +1026,26 @@ static inline u8 l2cap_get_auth_type(struct l2cap_chan *chan) } } +/* Raise the MIC length requested for the connection to the one the channel + * requires, so the next time encryption is started it asks for it. + */ +void l2cap_chan_req_mic_len(struct l2cap_chan *chan, struct hci_conn *hcon) +{ + if (chan->mic_len > hcon->req_mic_len) + hcon->req_mic_len = chan->mic_len; +} + /* Service level security */ int l2cap_chan_check_security(struct l2cap_chan *chan, bool initiator) { struct l2cap_conn *conn = chan->conn; __u8 auth_type; - if (conn->hcon->type == LE_LINK) + if (conn->hcon->type == LE_LINK) { + l2cap_chan_req_mic_len(chan, conn->hcon); + return smp_conn_security(conn->hcon, chan->sec_level); + } auth_type = l2cap_get_auth_type(chan); @@ -1512,6 +1525,8 @@ static void l2cap_le_start(struct l2cap_chan *chan) { struct l2cap_conn *conn = chan->conn; + l2cap_chan_req_mic_len(chan, conn->hcon); + if (!smp_conn_security(conn->hcon, chan->sec_level)) return; @@ -1579,6 +1594,18 @@ static bool l2cap_check_enc_key_size(struct hci_conn *hcon, hcon->enc_key_size >= min_key_size); } +static bool l2cap_check_mic_len(struct hci_conn *hcon, struct l2cap_chan *chan) +{ + /* If the channel has no MIC length requirement, skip check */ + if (!chan->mic_len) + return true; + + if (!test_bit(HCI_CONN_ENCRYPT, hcon->flags)) + return true; + + return hci_conn_mic_len(hcon) >= chan->mic_len; +} + static void l2cap_do_start(struct l2cap_chan *chan) __must_hold(&chan->lock) __must_hold(&chan->conn->lock) @@ -5119,6 +5146,7 @@ static int l2cap_le_connect_rsp(struct l2cap_conn *conn, /* We'll need to send a new Connect Request */ clear_bit(FLAG_LE_CONN_REQ_SENT, &chan->flags); + l2cap_chan_req_mic_len(chan, hcon); smp_conn_security(hcon, chan->sec_level); break; @@ -5283,6 +5311,13 @@ static int l2cap_le_connect_req(struct l2cap_conn *conn, goto response_unlock; } + /* Check if MIC length is sufficient for HDT PHY */ + if (!l2cap_check_mic_len(conn->hcon, pchan)) { + result = L2CAP_CR_LE_MIC_LEN_TOO_SHORT; + chan = NULL; + goto response_unlock; + } + /* Check for valid dynamic CID range */ if (scid < L2CAP_CID_DYN_START || scid > L2CAP_CID_LE_DYN_END) { result = L2CAP_CR_LE_INVALID_SCID; @@ -5501,6 +5536,12 @@ static inline int l2cap_ecred_conn_req(struct l2cap_conn *conn, goto unlock; } + /* Check if MIC length is sufficient */ + if (!l2cap_check_mic_len(conn->hcon, pchan)) { + result = L2CAP_CR_ECRED_MIC_LEN_TOO_SHORT; + goto unlock; + } + /* Check if the listening channel has set an output MTU then the * requested MTU shall be less than or equal to that value. */ @@ -5697,6 +5738,7 @@ static inline int l2cap_ecred_conn_rsp(struct l2cap_conn *conn, /* We'll need to send a new Connect Request */ clear_bit(FLAG_ECRED_CONN_REQ_SENT, &chan->flags); + l2cap_chan_req_mic_len(chan, hcon); smp_conn_security(hcon, chan->sec_level); break; diff --git a/net/bluetooth/l2cap_sock.c b/net/bluetooth/l2cap_sock.c index 7a2551ef7f50..2fa93e84dc91 100644 --- a/net/bluetooth/l2cap_sock.c +++ b/net/bluetooth/l2cap_sock.c @@ -623,8 +623,10 @@ static int l2cap_sock_getsockopt(struct socket *sock, int level, int optname, if (conn) { sec.level = conn->hcon->sec_level; - if (sk->sk_state == BT_CONNECTED) + if (sk->sk_state == BT_CONNECTED) { sec.key_size = conn->hcon->enc_key_size; + sec.mic_len = hci_conn_mic_len(conn->hcon); + } } else { sec.level = chan->sec_level; } @@ -960,9 +962,16 @@ static int l2cap_sock_setsockopt(struct socket *sock, int level, int optname, break; } - sec.level = BT_SECURITY_LOW; + /* mic_len was added at the end of struct bt_security, so + * accept the shorter struct as well, leaving mic_len unset. + */ + if (optlen < offsetofend(struct bt_security, key_size)) { + err = -EINVAL; + break; + } - err = copy_safe_from_sockptr(&sec, sizeof(sec), optval, optlen); + err = copy_struct_from_sockptr(&sec, sizeof(sec), optval, + optlen); if (err) break; @@ -972,7 +981,14 @@ static int l2cap_sock_setsockopt(struct socket *sock, int level, int optname, break; } + /* MIC_Length values: 32, 64 and 128 bits */ + if (sec.mic_len > 0x02) { + err = -EINVAL; + break; + } + chan->sec_level = sec.level; + chan->mic_len = sec.mic_len; conn = l2cap_chan_conn(chan); if (!conn) @@ -980,6 +996,7 @@ static int l2cap_sock_setsockopt(struct socket *sock, int level, int optname, /* change security for LE channels */ if (chan->scid == L2CAP_CID_ATT) { + l2cap_chan_req_mic_len(chan, conn->hcon); if (smp_conn_security(conn->hcon, sec.level)) { err = -EINVAL; break; diff --git a/net/bluetooth/rfcomm/sock.c b/net/bluetooth/rfcomm/sock.c index 3fb8b5474948..3ec2fb4ce580 100644 --- a/net/bluetooth/rfcomm/sock.c +++ b/net/bluetooth/rfcomm/sock.c @@ -700,9 +700,16 @@ static int rfcomm_sock_setsockopt(struct socket *sock, int level, int optname, break; } - sec.level = BT_SECURITY_LOW; + /* mic_len was added at the end of struct bt_security, so + * accept the shorter struct as well. RFCOMM ignores it. + */ + if (optlen < offsetofend(struct bt_security, key_size)) { + err = -EINVAL; + break; + } - err = copy_safe_from_sockptr(&sec, sizeof(sec), optval, optlen); + err = copy_struct_from_sockptr(&sec, sizeof(sec), optval, + optlen); if (err) break; @@ -844,8 +851,8 @@ static int rfcomm_sock_getsockopt(struct socket *sock, int level, int optname, break; } + memset(&sec, 0, sizeof(sec)); sec.level = rfcomm_pi(sk)->sec_level; - sec.key_size = 0; len = min(len, sizeof(sec)); if (copy_to_iter(&sec, len, &sopt->iter_out) != len) -- 2.56.0