From: Luiz Augusto von Dentz <luiz.von.dentz@xxxxxxxxx> Bluetooth Core Specification v5.2, Vol. 3, Part A, section 1.4, table 1.1: 'Start Fragments always either begin with the first octet of the Basic L2CAP header of a PDU or they have a length of zero (see [Vol 2] Part B, Section 6.6.2).' This text has been changed recently as it previously stated: 'Start Fragments always begin with the Basic L2CAP header of a PDU.' Apparently this was changed by the following errata: https://www.bluetooth.org/tse/errata_view.cfm?errata_id=10216 In past this has not been a problem but it seems new controllers are apparently doing it as it has been reported in Zephyr: https://github.com/zephyrproject-rtos/zephyr/issues/26900 Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@xxxxxxxxx> --- net/bluetooth/l2cap_core.c | 104 +++++++++++++++++++++++++++++-------- 1 file changed, 83 insertions(+), 21 deletions(-) diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c index ade83e224567..193bea314222 100644 --- a/net/bluetooth/l2cap_core.c +++ b/net/bluetooth/l2cap_core.c @@ -8269,6 +8269,63 @@ static void l2cap_security_cfm(struct hci_conn *hcon, u8 status, u8 encrypt) mutex_unlock(&conn->chan_lock); } +/* Append fragment into frame respecting the maximum len of rx_skb */ +static int l2cap_recv_frag(struct l2cap_conn *conn, struct sk_buff *skb, + u16 len) +{ + if (!conn->rx_skb) { + /* Allocate skb for the complete frame (with header) */ + conn->rx_skb = bt_skb_alloc(len, GFP_KERNEL); + if (!conn->rx_skb) + return -ENOMEM; + /* Init rx_len */ + conn->rx_len = len; + } + + /* Copy as much as the rx_skb can hold */ + len = min_t(u16, len, skb->len); + skb_copy_from_linear_data(skb, skb_put(conn->rx_skb, len), len); + skb_pull(skb, len); + conn->rx_len -= len; + + return len; +} + +static int l2cap_recv_header(struct l2cap_conn *conn, struct sk_buff *skb) +{ + struct l2cap_hdr *hdr; + struct sk_buff *rx_skb; + int len; + + /* Append just enough to complete the header */ + len = l2cap_recv_frag(conn, skb, L2CAP_HDR_SIZE - conn->rx_skb->len); + + /* If header could not be read just continue */ + if (len < 0 || conn->rx_skb->len < L2CAP_HDR_SIZE) + return len; + + rx_skb = conn->rx_skb; + conn->rx_skb = NULL; + + hdr = (struct l2cap_hdr *) rx_skb->data; + + /* Append existing rx_skb as that allocates only enough for the + * headers. + */ + len = l2cap_recv_frag(conn, rx_skb, + __le16_to_cpu(hdr->len) + L2CAP_HDR_SIZE); + kfree_skb(rx_skb); + + return len; +} + +static void l2cap_recv_reset(struct l2cap_conn *conn) +{ + kfree_skb(conn->rx_skb); + conn->rx_skb = NULL; + conn->rx_len = 0; +} + void l2cap_recv_acldata(struct hci_conn *hcon, struct sk_buff *skb, u16 flags) { struct l2cap_conn *conn = hcon->l2cap_data; @@ -8291,19 +8348,19 @@ void l2cap_recv_acldata(struct hci_conn *hcon, struct sk_buff *skb, u16 flags) case ACL_START: case ACL_START_NO_FLUSH: case ACL_COMPLETE: - if (conn->rx_len) { + if (conn->rx_skb) { BT_ERR("Unexpected start frame (len %d)", skb->len); - kfree_skb(conn->rx_skb); - conn->rx_skb = NULL; - conn->rx_len = 0; + l2cap_recv_reset(conn); l2cap_conn_unreliable(conn, ECOMM); } - /* Start fragment always begin with Basic L2CAP header */ + /* Start fragment may not contain the L2CAP header so just + * copy the initial byte when that happens. + */ if (skb->len < L2CAP_HDR_SIZE) { - BT_ERR("Frame is too short (len %d)", skb->len); - l2cap_conn_unreliable(conn, ECOMM); - goto drop; + if (l2cap_recv_frag(conn, skb, L2CAP_HDR_SIZE) < 0) + goto drop; + return; } hdr = (struct l2cap_hdr *) skb->data; @@ -8324,38 +8381,43 @@ void l2cap_recv_acldata(struct hci_conn *hcon, struct sk_buff *skb, u16 flags) goto drop; } - /* Allocate skb for the complete frame (with header) */ - conn->rx_skb = bt_skb_alloc(len, GFP_KERNEL); - if (!conn->rx_skb) + /* Append fragment into frame (with header) */ + if (l2cap_recv_frag(conn, skb, len) < 0) goto drop; - skb_copy_from_linear_data(skb, skb_put(conn->rx_skb, skb->len), - skb->len); - conn->rx_len = len - skb->len; break; case ACL_CONT: BT_DBG("Cont: frag len %d (expecting %d)", skb->len, conn->rx_len); - if (!conn->rx_len) { + if (!conn->rx_skb) { BT_ERR("Unexpected continuation frame (len %d)", skb->len); l2cap_conn_unreliable(conn, ECOMM); goto drop; } + /* Complete the L2CAP header if it has not been read */ + if (conn->rx_skb->len < L2CAP_HDR_SIZE) { + if (l2cap_recv_header(conn, skb) < 0) { + l2cap_conn_unreliable(conn, ECOMM); + goto drop; + } + + /* Header still could not be read just continue */ + if (conn->rx_skb->len < L2CAP_HDR_SIZE) + return; + } + if (skb->len > conn->rx_len) { BT_ERR("Fragment is too long (len %d, expected %d)", skb->len, conn->rx_len); - kfree_skb(conn->rx_skb); - conn->rx_skb = NULL; - conn->rx_len = 0; + l2cap_recv_reset(conn); l2cap_conn_unreliable(conn, ECOMM); goto drop; } - skb_copy_from_linear_data(skb, skb_put(conn->rx_skb, skb->len), - skb->len); - conn->rx_len -= skb->len; + /* Append fragment into frame (with header) */ + l2cap_recv_frag(conn, skb, skb->len); if (!conn->rx_len) { /* Complete frame received. l2cap_recv_frame -- 2.26.2
