1 // Copyright 2012 The Chromium Authors
2 // Use of this source code is governed by a BSD-style license that can be
3 // found in the LICENSE file.
4
5 #include "net/websockets/websocket_frame.h"
6
7 #include <stddef.h>
8 #include <string.h>
9
10 #include "base/big_endian.h"
11 #include "base/check_op.h"
12 #include "base/rand_util.h"
13 #include "base/ranges/algorithm.h"
14 #include "build/build_config.h"
15 #include "net/base/net_errors.h"
16
17 namespace net {
18
19 namespace {
20
21 // GCC (and Clang) can transparently use vector ops. Only try to do this on
22 // architectures where we know it works, otherwise gcc will attempt to emulate
23 // the vector ops, which is unlikely to be efficient.
24 #if defined(COMPILER_GCC) && \
25 (defined(ARCH_CPU_X86_FAMILY) || defined(ARCH_CPU_ARM_FAMILY))
26
27 using PackedMaskType = uint32_t __attribute__((vector_size(16)));
28
29 #else
30
31 using PackedMaskType = size_t;
32
33 #endif // defined(COMPILER_GCC) &&
34 // (defined(ARCH_CPU_X86_FAMILY) || defined(ARCH_CPU_ARM_FAMILY))
35
36 const uint8_t kFinalBit = 0x80;
37 const uint8_t kReserved1Bit = 0x40;
38 const uint8_t kReserved2Bit = 0x20;
39 const uint8_t kReserved3Bit = 0x10;
40 const uint8_t kOpCodeMask = 0xF;
41 const uint8_t kMaskBit = 0x80;
42 const uint64_t kMaxPayloadLengthWithoutExtendedLengthField = 125;
43 const uint64_t kPayloadLengthWithTwoByteExtendedLengthField = 126;
44 const uint64_t kPayloadLengthWithEightByteExtendedLengthField = 127;
45
MaskWebSocketFramePayloadByBytes(const WebSocketMaskingKey & masking_key,size_t masking_key_offset,char * const begin,char * const end)46 inline void MaskWebSocketFramePayloadByBytes(
47 const WebSocketMaskingKey& masking_key,
48 size_t masking_key_offset,
49 char* const begin,
50 char* const end) {
51 for (char* masked = begin; masked != end; ++masked) {
52 *masked ^= masking_key.key[masking_key_offset++ %
53 WebSocketFrameHeader::kMaskingKeyLength];
54 }
55 }
56
57 } // namespace
58
Clone() const59 std::unique_ptr<WebSocketFrameHeader> WebSocketFrameHeader::Clone() const {
60 auto ret = std::make_unique<WebSocketFrameHeader>(opcode);
61 ret->CopyFrom(*this);
62 return ret;
63 }
64
CopyFrom(const WebSocketFrameHeader & source)65 void WebSocketFrameHeader::CopyFrom(const WebSocketFrameHeader& source) {
66 final = source.final;
67 reserved1 = source.reserved1;
68 reserved2 = source.reserved2;
69 reserved3 = source.reserved3;
70 opcode = source.opcode;
71 masked = source.masked;
72 masking_key = source.masking_key;
73 payload_length = source.payload_length;
74 }
75
WebSocketFrame(WebSocketFrameHeader::OpCode opcode)76 WebSocketFrame::WebSocketFrame(WebSocketFrameHeader::OpCode opcode)
77 : header(opcode) {}
78
79 WebSocketFrame::~WebSocketFrame() = default;
80
81 WebSocketFrameChunk::WebSocketFrameChunk() = default;
82
83 WebSocketFrameChunk::~WebSocketFrameChunk() = default;
84
GetWebSocketFrameHeaderSize(const WebSocketFrameHeader & header)85 int GetWebSocketFrameHeaderSize(const WebSocketFrameHeader& header) {
86 int extended_length_size = 0;
87 if (header.payload_length > kMaxPayloadLengthWithoutExtendedLengthField &&
88 header.payload_length <= UINT16_MAX) {
89 extended_length_size = 2;
90 } else if (header.payload_length > UINT16_MAX) {
91 extended_length_size = 8;
92 }
93
94 return (WebSocketFrameHeader::kBaseHeaderSize + extended_length_size +
95 (header.masked ? WebSocketFrameHeader::kMaskingKeyLength : 0));
96 }
97
WriteWebSocketFrameHeader(const WebSocketFrameHeader & header,const WebSocketMaskingKey * masking_key,char * buffer,int buffer_size)98 int WriteWebSocketFrameHeader(const WebSocketFrameHeader& header,
99 const WebSocketMaskingKey* masking_key,
100 char* buffer,
101 int buffer_size) {
102 DCHECK((header.opcode & kOpCodeMask) == header.opcode)
103 << "header.opcode must fit to kOpCodeMask.";
104 DCHECK(header.payload_length <= static_cast<uint64_t>(INT64_MAX))
105 << "WebSocket specification doesn't allow a frame longer than "
106 << "INT64_MAX (0x7FFFFFFFFFFFFFFF) bytes.";
107 DCHECK_GE(buffer_size, 0);
108
109 // WebSocket frame format is as follows:
110 // - Common header (2 bytes)
111 // - Optional extended payload length
112 // (2 or 8 bytes, present if actual payload length is more than 125 bytes)
113 // - Optional masking key (4 bytes, present if MASK bit is on)
114 // - Actual payload (XOR masked with masking key if MASK bit is on)
115 //
116 // This function constructs frame header (the first three in the list
117 // above).
118
119 int header_size = GetWebSocketFrameHeaderSize(header);
120 if (header_size > buffer_size)
121 return ERR_INVALID_ARGUMENT;
122
123 int buffer_index = 0;
124
125 uint8_t first_byte = 0u;
126 first_byte |= header.final ? kFinalBit : 0u;
127 first_byte |= header.reserved1 ? kReserved1Bit : 0u;
128 first_byte |= header.reserved2 ? kReserved2Bit : 0u;
129 first_byte |= header.reserved3 ? kReserved3Bit : 0u;
130 first_byte |= header.opcode & kOpCodeMask;
131 buffer[buffer_index++] = first_byte;
132
133 int extended_length_size = 0;
134 uint8_t second_byte = 0u;
135 second_byte |= header.masked ? kMaskBit : 0u;
136 if (header.payload_length <= kMaxPayloadLengthWithoutExtendedLengthField) {
137 second_byte |= header.payload_length;
138 } else if (header.payload_length <= UINT16_MAX) {
139 second_byte |= kPayloadLengthWithTwoByteExtendedLengthField;
140 extended_length_size = 2;
141 } else {
142 second_byte |= kPayloadLengthWithEightByteExtendedLengthField;
143 extended_length_size = 8;
144 }
145 buffer[buffer_index++] = second_byte;
146
147 // Writes "extended payload length" field.
148 if (extended_length_size == 2) {
149 uint16_t payload_length_16 = static_cast<uint16_t>(header.payload_length);
150 base::WriteBigEndian(buffer + buffer_index, payload_length_16);
151 buffer_index += sizeof(payload_length_16);
152 } else if (extended_length_size == 8) {
153 base::WriteBigEndian(buffer + buffer_index, header.payload_length);
154 buffer_index += sizeof(header.payload_length);
155 }
156
157 // Writes "masking key" field, if needed.
158 if (header.masked) {
159 DCHECK(masking_key);
160 base::ranges::copy(masking_key->key, buffer + buffer_index);
161 buffer_index += WebSocketFrameHeader::kMaskingKeyLength;
162 } else {
163 DCHECK(!masking_key);
164 }
165
166 DCHECK_EQ(header_size, buffer_index);
167 return header_size;
168 }
169
GenerateWebSocketMaskingKey()170 WebSocketMaskingKey GenerateWebSocketMaskingKey() {
171 // Masking keys should be generated from a cryptographically secure random
172 // number generator, which means web application authors should not be able
173 // to guess the next value of masking key.
174 WebSocketMaskingKey masking_key;
175 base::RandBytes(masking_key.key, WebSocketFrameHeader::kMaskingKeyLength);
176 return masking_key;
177 }
178
MaskWebSocketFramePayload(const WebSocketMaskingKey & masking_key,uint64_t frame_offset,char * const data,int data_size)179 void MaskWebSocketFramePayload(const WebSocketMaskingKey& masking_key,
180 uint64_t frame_offset,
181 char* const data,
182 int data_size) {
183 static const size_t kMaskingKeyLength =
184 WebSocketFrameHeader::kMaskingKeyLength;
185
186 DCHECK_GE(data_size, 0);
187
188 // Most of the masking is done in chunks of sizeof(PackedMaskType), except for
189 // the beginning and the end of the buffer which may be unaligned.
190 // PackedMaskType must be a multiple of kMaskingKeyLength in size.
191 PackedMaskType packed_mask_key;
192 static const size_t kPackedMaskKeySize = sizeof(packed_mask_key);
193 static_assert((kPackedMaskKeySize >= kMaskingKeyLength &&
194 kPackedMaskKeySize % kMaskingKeyLength == 0),
195 "PackedMaskType size is not a multiple of mask length");
196 char* const end = data + data_size;
197 // If the buffer is too small for the vectorised version to be useful, revert
198 // to the byte-at-a-time implementation early.
199 if (data_size <= static_cast<int>(kPackedMaskKeySize * 2)) {
200 MaskWebSocketFramePayloadByBytes(
201 masking_key, frame_offset % kMaskingKeyLength, data, end);
202 return;
203 }
204 const size_t data_modulus =
205 reinterpret_cast<size_t>(data) % kPackedMaskKeySize;
206 char* const aligned_begin =
207 data_modulus == 0 ? data : (data + kPackedMaskKeySize - data_modulus);
208 // Guaranteed by the above check for small data_size.
209 DCHECK(aligned_begin < end);
210 MaskWebSocketFramePayloadByBytes(
211 masking_key, frame_offset % kMaskingKeyLength, data, aligned_begin);
212 const size_t end_modulus = reinterpret_cast<size_t>(end) % kPackedMaskKeySize;
213 char* const aligned_end = end - end_modulus;
214 // Guaranteed by the above check for small data_size.
215 DCHECK(aligned_end > aligned_begin);
216 // Create a version of the mask which is rotated by the appropriate offset
217 // for our alignment. The "trick" here is that 0 XORed with the mask will
218 // give the value of the mask for the appropriate byte.
219 char realigned_mask[kMaskingKeyLength] = {};
220 MaskWebSocketFramePayloadByBytes(
221 masking_key,
222 (frame_offset + aligned_begin - data) % kMaskingKeyLength,
223 realigned_mask,
224 realigned_mask + kMaskingKeyLength);
225
226 for (size_t i = 0; i < kPackedMaskKeySize; i += kMaskingKeyLength) {
227 // memcpy() is allegedly blessed by the C++ standard for type-punning.
228 memcpy(reinterpret_cast<char*>(&packed_mask_key) + i,
229 realigned_mask,
230 kMaskingKeyLength);
231 }
232
233 // The main loop.
234 for (char* merged = aligned_begin; merged != aligned_end;
235 merged += kPackedMaskKeySize) {
236 // This is not quite standard-compliant C++. However, the standard-compliant
237 // equivalent (using memcpy()) compiles to slower code using g++. In
238 // practice, this will work for the compilers and architectures currently
239 // supported by Chromium, and the tests are extremely unlikely to pass if a
240 // future compiler/architecture breaks it.
241 *reinterpret_cast<PackedMaskType*>(merged) ^= packed_mask_key;
242 }
243
244 MaskWebSocketFramePayloadByBytes(
245 masking_key,
246 (frame_offset + (aligned_end - data)) % kMaskingKeyLength,
247 aligned_end,
248 end);
249 }
250
251 } // namespace net
252