1// Copyright (c) 2013 The Chromium Authors. All rights reserved. 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/quic/crypto/strike_register.h" 6 7#include "base/logging.h" 8 9using std::pair; 10using std::set; 11using std::vector; 12 13namespace net { 14 15// static 16const uint32 StrikeRegister::kExternalNodeSize = 24; 17// static 18const uint32 StrikeRegister::kNil = (1 << 31) | 1; 19// static 20const uint32 StrikeRegister::kExternalFlag = 1 << 23; 21 22// InternalNode represents a non-leaf node in the critbit tree. See the comment 23// in the .h file for details. 24class StrikeRegister::InternalNode { 25 public: 26 void SetChild(unsigned direction, uint32 child) { 27 data_[direction] = (data_[direction] & 0xff) | (child << 8); 28 } 29 30 void SetCritByte(uint8 critbyte) { 31 data_[0] &= 0xffffff00; 32 data_[0] |= critbyte; 33 } 34 35 void SetOtherBits(uint8 otherbits) { 36 data_[1] &= 0xffffff00; 37 data_[1] |= otherbits; 38 } 39 40 void SetNextPtr(uint32 next) { data_[0] = next; } 41 42 uint32 next() const { return data_[0]; } 43 44 uint32 child(unsigned n) const { return data_[n] >> 8; } 45 46 uint8 critbyte() const { return data_[0]; } 47 48 uint8 otherbits() const { return data_[1]; } 49 50 // These bytes are organised thus: 51 // <24 bits> left child 52 // <8 bits> crit-byte 53 // <24 bits> right child 54 // <8 bits> other-bits 55 uint32 data_[2]; 56}; 57 58// kCreationTimeFromInternalEpoch contains the number of seconds between the 59// start of the internal epoch and the creation time. This allows us 60// to consider times that are before the creation time. 61static const uint32 kCreationTimeFromInternalEpoch = 63115200.0; // 2 years. 62 63void StrikeRegister::ValidateStrikeRegisterConfig(unsigned max_entries) { 64 // We only have 23 bits of index available. 65 CHECK_LT(max_entries, 1u << 23); 66 CHECK_GT(max_entries, 1u); // There must be at least two entries. 67 CHECK_EQ(sizeof(InternalNode), 8u); // in case of compiler changes. 68} 69 70StrikeRegister::StrikeRegister(unsigned max_entries, 71 uint32 current_time, 72 uint32 window_secs, 73 const uint8 orbit[8], 74 StartupType startup) 75 : max_entries_(max_entries), 76 window_secs_(window_secs), 77 internal_epoch_(current_time > kCreationTimeFromInternalEpoch 78 ? current_time - kCreationTimeFromInternalEpoch 79 : 0), 80 // The horizon is initially set |window_secs| into the future because, if 81 // we just crashed, then we may have accepted nonces in the span 82 // [current_time...current_time+window_secs) and so we conservatively 83 // reject the whole timespan unless |startup| tells us otherwise. 84 horizon_(ExternalTimeToInternal(current_time) + window_secs), 85 horizon_valid_(startup == DENY_REQUESTS_AT_STARTUP) { 86 memcpy(orbit_, orbit, sizeof(orbit_)); 87 88 ValidateStrikeRegisterConfig(max_entries); 89 internal_nodes_ = new InternalNode[max_entries]; 90 external_nodes_.reset(new uint8[kExternalNodeSize * max_entries]); 91 92 Reset(); 93} 94 95StrikeRegister::~StrikeRegister() { delete[] internal_nodes_; } 96 97void StrikeRegister::Reset() { 98 // Thread a free list through all of the internal nodes. 99 internal_node_free_head_ = 0; 100 for (unsigned i = 0; i < max_entries_ - 1; i++) 101 internal_nodes_[i].SetNextPtr(i + 1); 102 internal_nodes_[max_entries_ - 1].SetNextPtr(kNil); 103 104 // Also thread a free list through the external nodes. 105 external_node_free_head_ = 0; 106 for (unsigned i = 0; i < max_entries_ - 1; i++) 107 external_node_next_ptr(i) = i + 1; 108 external_node_next_ptr(max_entries_ - 1) = kNil; 109 110 // This is the root of the tree. 111 internal_node_head_ = kNil; 112} 113 114bool StrikeRegister::Insert(const uint8 nonce[32], 115 const uint32 current_time_external) { 116 const uint32 current_time = ExternalTimeToInternal(current_time_external); 117 118 // Check to see if the orbit is correct. 119 if (memcmp(nonce + sizeof(current_time), orbit_, sizeof(orbit_))) { 120 return false; 121 } 122 const uint32 nonce_time = ExternalTimeToInternal(TimeFromBytes(nonce)); 123 // We have dropped one or more nonces with a time value of |horizon_|, so 124 // we have to reject anything with a timestamp less than or equal to that. 125 if (horizon_valid_ && nonce_time <= horizon_) { 126 return false; 127 } 128 129 // Check that the timestamp is in the current window. 130 if ((current_time > window_secs_ && 131 nonce_time < (current_time - window_secs_)) || 132 nonce_time > (current_time + window_secs_)) { 133 return false; 134 } 135 136 // We strip the orbit out of the nonce. 137 uint8 value[24]; 138 memcpy(value, &nonce_time, sizeof(nonce_time)); 139 memcpy(value + sizeof(nonce_time), 140 nonce + sizeof(nonce_time) + sizeof(orbit_), 141 sizeof(value) - sizeof(nonce_time)); 142 143 // Find the best match to |value| in the crit-bit tree. The best match is 144 // simply the value which /could/ match |value|, if any does, so we still 145 // need a memcmp to check. 146 uint32 best_match_index = BestMatch(value); 147 if (best_match_index == kNil) { 148 // Empty tree. Just insert the new value at the root. 149 uint32 index = GetFreeExternalNode(); 150 memcpy(external_node(index), value, sizeof(value)); 151 internal_node_head_ = (index | kExternalFlag) << 8; 152 return true; 153 } 154 155 const uint8* best_match = external_node(best_match_index); 156 if (memcmp(best_match, value, sizeof(value)) == 0) { 157 // We found the value in the tree. 158 return false; 159 } 160 161 // We are going to insert a new entry into the tree, so get the nodes now. 162 uint32 internal_node_index = GetFreeInternalNode(); 163 uint32 external_node_index = GetFreeExternalNode(); 164 165 // If we just evicted the best match, then we have to try and match again. 166 // We know that we didn't just empty the tree because we require that 167 // max_entries_ >= 2. Also, we know that it doesn't match because, if it 168 // did, it would have been returned previously. 169 if (external_node_index == best_match_index) { 170 best_match_index = BestMatch(value); 171 best_match = external_node(best_match_index); 172 } 173 174 // Now we need to find the first bit where we differ from |best_match|. 175 unsigned differing_byte; 176 uint8 new_other_bits; 177 for (differing_byte = 0; differing_byte < sizeof(value); differing_byte++) { 178 new_other_bits = value[differing_byte] ^ best_match[differing_byte]; 179 if (new_other_bits) { 180 break; 181 } 182 } 183 184 // Once we have the XOR the of first differing byte in new_other_bits we need 185 // to find the most significant differing bit. We could do this with a simple 186 // for loop, testing bits 7..0. Instead we fold the bits so that we end up 187 // with a byte where all the bits below the most significant one, are set. 188 new_other_bits |= new_other_bits >> 1; 189 new_other_bits |= new_other_bits >> 2; 190 new_other_bits |= new_other_bits >> 4; 191 // Now this bit trick results in all the bits set, except the original 192 // most-significant one. 193 new_other_bits = (new_other_bits & ~(new_other_bits >> 1)) ^ 255; 194 195 // Consider the effect of ORing against |new_other_bits|. If |value| did not 196 // have the critical bit set, the result is the same as |new_other_bits|. If 197 // it did, the result is all ones. 198 199 unsigned newdirection; 200 if ((new_other_bits | value[differing_byte]) == 0xff) { 201 newdirection = 1; 202 } else { 203 newdirection = 0; 204 } 205 206 memcpy(external_node(external_node_index), value, sizeof(value)); 207 InternalNode* inode = &internal_nodes_[internal_node_index]; 208 209 inode->SetChild(newdirection, external_node_index | kExternalFlag); 210 inode->SetCritByte(differing_byte); 211 inode->SetOtherBits(new_other_bits); 212 213 // |where_index| is a pointer to the uint32 which needs to be updated in 214 // order to insert the new internal node into the tree. The internal nodes 215 // store the child indexes in the top 24-bits of a 32-bit word and, to keep 216 // the code simple, we define that |internal_node_head_| is organised the 217 // same way. 218 DCHECK_EQ(internal_node_head_ & 0xff, 0u); 219 uint32* where_index = &internal_node_head_; 220 while (((*where_index >> 8) & kExternalFlag) == 0) { 221 InternalNode* node = &internal_nodes_[*where_index >> 8]; 222 if (node->critbyte() > differing_byte) { 223 break; 224 } 225 if (node->critbyte() == differing_byte && 226 node->otherbits() > new_other_bits) { 227 break; 228 } 229 if (node->critbyte() == differing_byte && 230 node->otherbits() == new_other_bits) { 231 CHECK(false); 232 } 233 234 uint8 c = value[node->critbyte()]; 235 const int direction = 236 (1 + static_cast<unsigned>(node->otherbits() | c)) >> 8; 237 where_index = &node->data_[direction]; 238 } 239 240 inode->SetChild(newdirection ^ 1, *where_index >> 8); 241 *where_index = (*where_index & 0xff) | (internal_node_index << 8); 242 243 return true; 244} 245 246const uint8* StrikeRegister::orbit() const { 247 return orbit_; 248} 249 250void StrikeRegister::Validate() { 251 set<uint32> free_internal_nodes; 252 for (uint32 i = internal_node_free_head_; i != kNil; 253 i = internal_nodes_[i].next()) { 254 CHECK_LT(i, max_entries_); 255 CHECK_EQ(free_internal_nodes.count(i), 0u); 256 free_internal_nodes.insert(i); 257 } 258 259 set<uint32> free_external_nodes; 260 for (uint32 i = external_node_free_head_; i != kNil; 261 i = external_node_next_ptr(i)) { 262 CHECK_LT(i, max_entries_); 263 CHECK_EQ(free_external_nodes.count(i), 0u); 264 free_external_nodes.insert(i); 265 } 266 267 set<uint32> used_external_nodes; 268 set<uint32> used_internal_nodes; 269 270 if (internal_node_head_ != kNil && 271 ((internal_node_head_ >> 8) & kExternalFlag) == 0) { 272 vector<pair<unsigned, bool> > bits; 273 ValidateTree(internal_node_head_ >> 8, -1, bits, free_internal_nodes, 274 free_external_nodes, &used_internal_nodes, 275 &used_external_nodes); 276 } 277} 278 279// static 280uint32 StrikeRegister::TimeFromBytes(const uint8 d[4]) { 281 return static_cast<uint32>(d[0]) << 24 | 282 static_cast<uint32>(d[1]) << 16 | 283 static_cast<uint32>(d[2]) << 8 | 284 static_cast<uint32>(d[3]); 285} 286 287uint32 StrikeRegister::ExternalTimeToInternal(uint32 external_time) { 288 return external_time - internal_epoch_; 289} 290 291uint32 StrikeRegister::BestMatch(const uint8 v[24]) const { 292 if (internal_node_head_ == kNil) { 293 return kNil; 294 } 295 296 uint32 next = internal_node_head_ >> 8; 297 while ((next & kExternalFlag) == 0) { 298 InternalNode* node = &internal_nodes_[next]; 299 uint8 b = v[node->critbyte()]; 300 unsigned direction = 301 (1 + static_cast<unsigned>(node->otherbits() | b)) >> 8; 302 next = node->child(direction); 303 } 304 305 return next & ~kExternalFlag; 306} 307 308uint32& StrikeRegister::external_node_next_ptr(unsigned i) { 309 return *reinterpret_cast<uint32*>(&external_nodes_[i * kExternalNodeSize]); 310} 311 312uint8* StrikeRegister::external_node(unsigned i) { 313 return &external_nodes_[i * kExternalNodeSize]; 314} 315 316uint32 StrikeRegister::GetFreeExternalNode() { 317 uint32 index = external_node_free_head_; 318 if (index == kNil) { 319 DropNode(); 320 return GetFreeExternalNode(); 321 } 322 323 external_node_free_head_ = external_node_next_ptr(index); 324 return index; 325} 326 327uint32 StrikeRegister::GetFreeInternalNode() { 328 uint32 index = internal_node_free_head_; 329 if (index == kNil) { 330 DropNode(); 331 return GetFreeInternalNode(); 332 } 333 334 internal_node_free_head_ = internal_nodes_[index].next(); 335 return index; 336} 337 338void StrikeRegister::DropNode() { 339 // DropNode should never be called on an empty tree. 340 DCHECK(internal_node_head_ != kNil); 341 342 // An internal node in a crit-bit tree always has exactly two children. 343 // This means that, if we are removing an external node (which is one of 344 // those children), then we also need to remove an internal node. In order 345 // to do that we keep pointers to the parent (wherep) and grandparent 346 // (whereq) when walking down the tree. 347 348 uint32 p = internal_node_head_ >> 8, *wherep = &internal_node_head_, 349 *whereq = NULL; 350 while ((p & kExternalFlag) == 0) { 351 whereq = wherep; 352 InternalNode* inode = &internal_nodes_[p]; 353 // We always go left, towards the smallest element, exploiting the fact 354 // that the timestamp is big-endian and at the start of the value. 355 wherep = &inode->data_[0]; 356 p = (*wherep) >> 8; 357 } 358 359 const uint32 ext_index = p & ~kExternalFlag; 360 const uint8* ext_node = external_node(ext_index); 361 horizon_ = TimeFromBytes(ext_node); 362 363 if (!whereq) { 364 // We are removing the last element in a tree. 365 internal_node_head_ = kNil; 366 FreeExternalNode(ext_index); 367 return; 368 } 369 370 // |wherep| points to the left child pointer in the parent so we can add 371 // one and dereference to get the right child. 372 const uint32 other_child = wherep[1]; 373 FreeInternalNode((*whereq) >> 8); 374 *whereq = (*whereq & 0xff) | (other_child & 0xffffff00); 375 FreeExternalNode(ext_index); 376} 377 378void StrikeRegister::FreeExternalNode(uint32 index) { 379 external_node_next_ptr(index) = external_node_free_head_; 380 external_node_free_head_ = index; 381} 382 383void StrikeRegister::FreeInternalNode(uint32 index) { 384 internal_nodes_[index].SetNextPtr(internal_node_free_head_); 385 internal_node_free_head_ = index; 386} 387 388void StrikeRegister::ValidateTree( 389 uint32 internal_node, 390 int last_bit, 391 const vector<pair<unsigned, bool> >& bits, 392 const set<uint32>& free_internal_nodes, 393 const set<uint32>& free_external_nodes, 394 set<uint32>* used_internal_nodes, 395 set<uint32>* used_external_nodes) { 396 CHECK_LT(internal_node, max_entries_); 397 const InternalNode* i = &internal_nodes_[internal_node]; 398 unsigned bit = 0; 399 switch (i->otherbits()) { 400 case 0xff & ~(1 << 7): 401 bit = 0; 402 break; 403 case 0xff & ~(1 << 6): 404 bit = 1; 405 break; 406 case 0xff & ~(1 << 5): 407 bit = 2; 408 break; 409 case 0xff & ~(1 << 4): 410 bit = 3; 411 break; 412 case 0xff & ~(1 << 3): 413 bit = 4; 414 break; 415 case 0xff & ~(1 << 2): 416 bit = 5; 417 break; 418 case 0xff & ~(1 << 1): 419 bit = 6; 420 break; 421 case 0xff & ~1: 422 bit = 7; 423 break; 424 default: 425 CHECK(false); 426 } 427 428 bit += 8 * i->critbyte(); 429 if (last_bit > -1) { 430 CHECK_GT(bit, static_cast<unsigned>(last_bit)); 431 } 432 433 CHECK_EQ(free_internal_nodes.count(internal_node), 0u); 434 435 for (unsigned child = 0; child < 2; child++) { 436 if (i->child(child) & kExternalFlag) { 437 uint32 ext = i->child(child) & ~kExternalFlag; 438 CHECK_EQ(free_external_nodes.count(ext), 0u); 439 CHECK_EQ(used_external_nodes->count(ext), 0u); 440 used_external_nodes->insert(ext); 441 const uint8* bytes = external_node(ext); 442 for (vector<pair<unsigned, bool> >::const_iterator i = bits.begin(); 443 i != bits.end(); i++) { 444 unsigned byte = i->first / 8; 445 DCHECK_LE(byte, 0xffu); 446 unsigned bit = i->first % 8; 447 static const uint8 kMasks[8] = 448 {0x80, 0x40, 0x20, 0x10, 0x08, 0x04, 0x02, 0x01}; 449 CHECK_EQ((bytes[byte] & kMasks[bit]) != 0, i->second); 450 } 451 } else { 452 uint32 inter = i->child(child); 453 vector<pair<unsigned, bool> > new_bits(bits); 454 new_bits.push_back(pair<unsigned, bool>(bit, child != 0)); 455 CHECK_EQ(free_internal_nodes.count(inter), 0u); 456 CHECK_EQ(used_internal_nodes->count(inter), 0u); 457 used_internal_nodes->insert(inter); 458 ValidateTree(inter, bit, bits, free_internal_nodes, free_external_nodes, 459 used_internal_nodes, used_external_nodes); 460 } 461 } 462} 463 464} // namespace net 465