1 /******************************************************************************
2 *
3 * Copyright 2014 Google, Inc.
4 *
5 * Licensed under the Apache License, Version 2.0 (the "License");
6 * you may not use this file except in compliance with the License.
7 * You may obtain a copy of the License at:
8 *
9 * http://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
16 *
17 ******************************************************************************/
18
19 #define LOG_TAG "bt_hci_packet_fragmenter"
20
21 #include "packet_fragmenter.h"
22
23 #include <base/logging.h>
24 #include <string.h>
25 #include <unordered_map>
26
27 #include "bt_target.h"
28 #include "buffer_allocator.h"
29 #include "device/include/controller.h"
30 #include "hci_internals.h"
31 #include "osi/include/log.h"
32 #include "osi/include/osi.h"
33
34 #define APPLY_CONTINUATION_FLAG(handle) (((handle)&0xCFFF) | 0x1000)
35 #define APPLY_START_FLAG(handle) (((handle)&0xCFFF) | 0x2000)
36 #define SUB_EVENT(event) ((event)&MSG_SUB_EVT_MASK)
37 #define GET_BOUNDARY_FLAG(handle) (((handle) >> 12) & 0x0003)
38
39 #define HANDLE_MASK 0x0FFF
40 #define START_PACKET_BOUNDARY 2
41 #define CONTINUATION_PACKET_BOUNDARY 1
42 #define L2CAP_HEADER_PDU_LEN_SIZE 2
43 #define L2CAP_HEADER_CID_SIZE 2
44 #define L2CAP_HEADER_SIZE (L2CAP_HEADER_PDU_LEN_SIZE + L2CAP_HEADER_CID_SIZE)
45
46 // Our interface and callbacks
47
48 static const allocator_t* buffer_allocator;
49 static const controller_t* controller;
50 static const packet_fragmenter_callbacks_t* callbacks;
51
52 static std::unordered_map<uint16_t /* handle */, BT_HDR*> partial_packets;
53
init(const packet_fragmenter_callbacks_t * result_callbacks)54 static void init(const packet_fragmenter_callbacks_t* result_callbacks) {
55 callbacks = result_callbacks;
56 }
57
cleanup()58 static void cleanup() { partial_packets.clear(); }
59
fragment_and_dispatch(BT_HDR * packet)60 static void fragment_and_dispatch(BT_HDR* packet) {
61 CHECK(packet != NULL);
62
63 uint16_t event = packet->event & MSG_EVT_MASK;
64 uint8_t* stream = packet->data + packet->offset;
65
66 // We only fragment ACL packets
67 if (event != MSG_STACK_TO_HC_HCI_ACL) {
68 callbacks->fragmented(packet, true);
69 return;
70 }
71
72 uint16_t max_data_size =
73 SUB_EVENT(packet->event) == LOCAL_BR_EDR_CONTROLLER_ID
74 ? controller->get_acl_data_size_classic()
75 : controller->get_acl_data_size_ble();
76
77 uint16_t max_packet_size = max_data_size + HCI_ACL_PREAMBLE_SIZE;
78 uint16_t remaining_length = packet->len;
79
80 uint16_t continuation_handle;
81 STREAM_TO_UINT16(continuation_handle, stream);
82 continuation_handle = APPLY_CONTINUATION_FLAG(continuation_handle);
83
84 while (remaining_length > max_packet_size) {
85 // Make sure we use the right ACL packet size
86 stream = packet->data + packet->offset;
87 STREAM_SKIP_UINT16(stream);
88 UINT16_TO_STREAM(stream, max_data_size);
89
90 packet->len = max_packet_size;
91 callbacks->fragmented(packet, false);
92
93 packet->offset += max_data_size;
94 remaining_length -= max_data_size;
95 packet->len = remaining_length;
96
97 // Write the ACL header for the next fragment
98 stream = packet->data + packet->offset;
99 UINT16_TO_STREAM(stream, continuation_handle);
100 UINT16_TO_STREAM(stream, remaining_length - HCI_ACL_PREAMBLE_SIZE);
101
102 // Apparently L2CAP can set layer_specific to a max number of segments to
103 // transmit
104 if (packet->layer_specific) {
105 packet->layer_specific--;
106
107 if (packet->layer_specific == 0) {
108 packet->event = MSG_HC_TO_STACK_L2C_SEG_XMIT;
109 callbacks->transmit_finished(packet, false);
110 return;
111 }
112 }
113 }
114
115 callbacks->fragmented(packet, true);
116 }
117
check_uint16_overflow(uint16_t a,uint16_t b)118 static bool check_uint16_overflow(uint16_t a, uint16_t b) {
119 return (UINT16_MAX - a) < b;
120 }
121
reassemble_and_dispatch(UNUSED_ATTR BT_HDR * packet)122 static void reassemble_and_dispatch(UNUSED_ATTR BT_HDR* packet) {
123 if ((packet->event & MSG_EVT_MASK) == MSG_HC_TO_STACK_HCI_ACL) {
124 uint8_t* stream = packet->data;
125 uint16_t handle;
126 uint16_t acl_length;
127
128 STREAM_TO_UINT16(handle, stream);
129 STREAM_TO_UINT16(acl_length, stream);
130
131 CHECK(acl_length == packet->len - HCI_ACL_PREAMBLE_SIZE);
132
133 uint8_t boundary_flag = GET_BOUNDARY_FLAG(handle);
134 handle = handle & HANDLE_MASK;
135
136 if (boundary_flag == START_PACKET_BOUNDARY) {
137 if (acl_length < 2) {
138 LOG_WARN(LOG_TAG, "%s invalid acl_length %d", __func__, acl_length);
139 buffer_allocator->free(packet);
140 return;
141 }
142 uint16_t l2cap_length;
143 STREAM_TO_UINT16(l2cap_length, stream);
144 auto map_iter = partial_packets.find(handle);
145 if (map_iter != partial_packets.end()) {
146 LOG_WARN(LOG_TAG,
147 "%s found unfinished packet for handle with start packet. "
148 "Dropping old.",
149 __func__);
150
151 BT_HDR* hdl = map_iter->second;
152 partial_packets.erase(map_iter);
153 buffer_allocator->free(hdl);
154 }
155
156 if (acl_length < L2CAP_HEADER_PDU_LEN_SIZE) {
157 LOG_WARN(LOG_TAG, "%s L2CAP packet too small (%d < %d). Dropping it.",
158 __func__, packet->len, L2CAP_HEADER_PDU_LEN_SIZE);
159 buffer_allocator->free(packet);
160 return;
161 }
162
163 uint16_t full_length =
164 l2cap_length + L2CAP_HEADER_SIZE + HCI_ACL_PREAMBLE_SIZE;
165
166 // Check for buffer overflow and that the full packet size + BT_HDR size
167 // is less than the max buffer size
168 if (check_uint16_overflow(l2cap_length,
169 (L2CAP_HEADER_SIZE + HCI_ACL_PREAMBLE_SIZE)) ||
170 ((full_length + sizeof(BT_HDR)) > BT_DEFAULT_BUFFER_SIZE)) {
171 LOG_ERROR(LOG_TAG, "%s Dropping L2CAP packet with invalid length (%d).",
172 __func__, l2cap_length);
173 buffer_allocator->free(packet);
174 return;
175 }
176
177 if (full_length <= packet->len) {
178 if (full_length < packet->len)
179 LOG_WARN(LOG_TAG,
180 "%s found l2cap full length %d less than the hci length %d.",
181 __func__, l2cap_length, packet->len);
182
183 callbacks->reassembled(packet);
184 return;
185 }
186
187 BT_HDR* partial_packet =
188 (BT_HDR*)buffer_allocator->alloc(full_length + sizeof(BT_HDR));
189 partial_packet->event = packet->event;
190 partial_packet->len = full_length;
191 partial_packet->offset = packet->len;
192
193 memcpy(partial_packet->data, packet->data, packet->len);
194
195 // Update the ACL data size to indicate the full expected length
196 stream = partial_packet->data;
197 STREAM_SKIP_UINT16(stream); // skip the handle
198 UINT16_TO_STREAM(stream, full_length - HCI_ACL_PREAMBLE_SIZE);
199
200 partial_packets[handle] = partial_packet;
201
202 // Free the old packet buffer, since we don't need it anymore
203 buffer_allocator->free(packet);
204 } else {
205 auto map_iter = partial_packets.find(handle);
206 if (map_iter == partial_packets.end()) {
207 LOG_WARN(LOG_TAG,
208 "%s got continuation for unknown packet. Dropping it.",
209 __func__);
210 buffer_allocator->free(packet);
211 return;
212 }
213 BT_HDR* partial_packet = map_iter->second;
214
215 packet->offset = HCI_ACL_PREAMBLE_SIZE;
216 uint16_t projected_offset =
217 partial_packet->offset + (packet->len - HCI_ACL_PREAMBLE_SIZE);
218 if (projected_offset >
219 partial_packet->len) { // len stores the expected length
220 LOG_WARN(LOG_TAG,
221 "%s got packet which would exceed expected length of %d. "
222 "Truncating.",
223 __func__, partial_packet->len);
224 packet->len =
225 (partial_packet->len - partial_packet->offset) + packet->offset;
226 projected_offset = partial_packet->len;
227 }
228
229 memcpy(partial_packet->data + partial_packet->offset,
230 packet->data + packet->offset, packet->len - packet->offset);
231
232 // Free the old packet buffer, since we don't need it anymore
233 buffer_allocator->free(packet);
234 partial_packet->offset = projected_offset;
235
236 if (partial_packet->offset == partial_packet->len) {
237 partial_packets.erase(handle);
238 partial_packet->offset = 0;
239 callbacks->reassembled(partial_packet);
240 }
241 }
242 } else {
243 callbacks->reassembled(packet);
244 }
245 }
246
247 static const packet_fragmenter_t interface = {init, cleanup,
248
249 fragment_and_dispatch,
250 reassemble_and_dispatch};
251
packet_fragmenter_get_interface()252 const packet_fragmenter_t* packet_fragmenter_get_interface() {
253 controller = controller_get_interface();
254 buffer_allocator = buffer_allocator_get_interface();
255 return &interface;
256 }
257
packet_fragmenter_get_test_interface(const controller_t * controller_interface,const allocator_t * buffer_allocator_interface)258 const packet_fragmenter_t* packet_fragmenter_get_test_interface(
259 const controller_t* controller_interface,
260 const allocator_t* buffer_allocator_interface) {
261 controller = controller_interface;
262 buffer_allocator = buffer_allocator_interface;
263 return &interface;
264 }
265