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Merge #18512: Improve asmap checks and add sanity check

Browse Source 
748977690e Add asmap_direct fuzzer that tests Interpreter directly (Pieter Wuille)
7cf97fda15 Make asmap Interpreter errors fatal and fuzz test it (Pieter Wuille)
c81aefc537 Add additional effiency checks to sanity checker (Pieter Wuille)
fffd8dca2d Add asmap sanity checker (Pieter Wuille)
5feefbe6e7 Improve asmap Interpret checks and document failures (Pieter Wuille)
2b3dbfa5a6 Deal with decoding failures explicitly in asmap Interpret (Pieter Wuille)
1479007a33 Introduce Instruction enum in asmap (Pieter Wuille)

Pull request description:

  This improves/documents the failure cases inside the asmap interpreter. None of the changes are bug fixes (they only change behavior for corrupted asmap files), but they may make things easier to follow.

  In a second step, a sanity checker is added that effectively executes every potential code path through the asmap file, checking the same failure cases as the interpreter, and more. It takes around 30 ms to run for me for a 1.2 MB asmap file.

  I've verified that this accepts asmap files constructed by https://github.com/sipa/asmap/blob/master/buildmap.py with a large dataset, and no longer accepts it with 1 bit changed in it.

ACKs for top commit:
  practicalswift:
    ACK 748977690e modulo feedback below.
  jonatack:
    ACK 748977690e code review, regular build/tests/ran bitcoin with -asmap, fuzz build/ran both fuzzers overnight.
  fjahr:
    ACK 748977690e

Tree-SHA512: d876df3859735795c857c83e7155ba6851ce839bdfa10c18ce2698022cc493ce024b5578c1828e2a94bcdf2552c2f46c392a251ed086691b41959e62a6970821
This commit is contained in:
Wladimir J. van der Laan
2020-05-06 14:37:19 +02:00
parent 88b2652fad 748977690e
commit f763283b65
8 changed files with 199 additions and 27 deletions
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112
src/util/asmap.cpp
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@@ -2,12 +2,15 @@
// Distributed under the MIT software license, see the accompanying
// file COPYING or http://www.opensource.org/licenses/mit-license.php.
#include <map>
#include <vector>
#include <assert.h>
#include <crypto/common.h>
namespace {
constexpr uint32_t INVALID = 0xFFFFFFFF;
uint32_t DecodeBits(std::vector<bool>::const_iterator& bitpos, const std::vector<bool>::const_iterator& endpos, uint8_t minval, const std::vector<uint8_t> &bit_sizes)
{
uint32_t val = minval;
@@ -25,7 +28,7 @@ uint32_t DecodeBits(std::vector<bool>::const_iterator& bitpos, const std::vector
val += (1 << *bit_sizes_it);
} else {
for (int b = 0; b < *bit_sizes_it; b++) {
if (bitpos == endpos) break;
if (bitpos == endpos) return INVALID; // Reached EOF in mantissa
bit = *bitpos;
bitpos++;
val += bit << (*bit_sizes_it - 1 - b);
@@ -33,13 +36,21 @@ uint32_t DecodeBits(std::vector<bool>::const_iterator& bitpos, const std::vector
return val;
}
}
return -1;
return INVALID; // Reached EOF in exponent
}
const std::vector<uint8_t> TYPE_BIT_SIZES{0, 0, 1};
uint32_t DecodeType(std::vector<bool>::const_iterator& bitpos, const std::vector<bool>::const_iterator& endpos)
enum class Instruction : uint32_t
{
return DecodeBits(bitpos, endpos, 0, TYPE_BIT_SIZES);
RETURN = 0,
JUMP = 1,
MATCH = 2,
DEFAULT = 3,
};
const std::vector<uint8_t> TYPE_BIT_SIZES{0, 0, 1};
Instruction DecodeType(std::vector<bool>::const_iterator& bitpos, const std::vector<bool>::const_iterator& endpos)
{
return Instruction(DecodeBits(bitpos, endpos, 0, TYPE_BIT_SIZES));
}
const std::vector<uint8_t> ASN_BIT_SIZES{15, 16, 17, 18, 19, 20, 21, 22, 23, 24};
@@ -70,34 +81,105 @@ uint32_t Interpret(const std::vector<bool> &asmap, const std::vector<bool> &ip)
const std::vector<bool>::const_iterator endpos = asmap.end();
uint8_t bits = ip.size();
uint32_t default_asn = 0;
uint32_t opcode, jump, match, matchlen;
uint32_t jump, match, matchlen;
Instruction opcode;
while (pos != endpos) {
opcode = DecodeType(pos, endpos);
if (opcode == 0) {
return DecodeASN(pos, endpos);
} else if (opcode == 1) {
if (opcode == Instruction::RETURN) {
default_asn = DecodeASN(pos, endpos);
if (default_asn == INVALID) break; // ASN straddles EOF
return default_asn;
} else if (opcode == Instruction::JUMP) {
jump = DecodeJump(pos, endpos);
if (bits == 0) break;
if (jump == INVALID) break; // Jump offset straddles EOF
if (bits == 0) break; // No input bits left
if (jump >= endpos - pos) break; // Jumping past EOF
if (ip[ip.size() - bits]) {
if (jump >= endpos - pos) break;
pos += jump;
}
bits--;
} else if (opcode == 2) {
} else if (opcode == Instruction::MATCH) {
match = DecodeMatch(pos, endpos);
if (match == INVALID) break; // Match bits straddle EOF
matchlen = CountBits(match) - 1;
if (bits < matchlen) break; // Not enough input bits
for (uint32_t bit = 0; bit < matchlen; bit++) {
if (bits == 0) break;
if ((ip[ip.size() - bits]) != ((match >> (matchlen - 1 - bit)) & 1)) {
return default_asn;
}
bits--;
}
} else if (opcode == 3) {
} else if (opcode == Instruction::DEFAULT) {
default_asn = DecodeASN(pos, endpos);
if (default_asn == INVALID) break; // ASN straddles EOF
} else {
break;
break; // Instruction straddles EOF
}
}
assert(false); // Reached EOF without RETURN, or aborted (see any of the breaks above) - should have been caught by SanityCheckASMap below
return 0; // 0 is not a valid ASN
}
bool SanityCheckASMap(const std::vector<bool>& asmap, int bits)
{
const std::vector<bool>::const_iterator begin = asmap.begin(), endpos = asmap.end();
std::vector<bool>::const_iterator pos = begin;
std::vector<std::pair<uint32_t, int>> jumps; // All future positions we may jump to (bit offset in asmap -> bits to consume left)
jumps.reserve(bits);
Instruction prevopcode = Instruction::JUMP;
bool had_incomplete_match = false;
while (pos != endpos) {
uint32_t offset = pos - begin;
if (!jumps.empty() && offset >= jumps.back().first) return false; // There was a jump into the middle of the previous instruction
Instruction opcode = DecodeType(pos, endpos);
if (opcode == Instruction::RETURN) {
if (prevopcode == Instruction::DEFAULT) return false; // There should not be any RETURN immediately after a DEFAULT (could be combined into just RETURN)
uint32_t asn = DecodeASN(pos, endpos);
if (asn == INVALID) return false; // ASN straddles EOF
if (jumps.empty()) {
// Nothing to execute anymore
if (endpos - pos > 7) return false; // Excessive padding
while (pos != endpos) {
if (*pos) return false; // Nonzero padding bit
++pos;
}
return true; // Sanely reached EOF
} else {
// Continue by pretending we jumped to the next instruction
offset = pos - begin;
if (offset != jumps.back().first) return false; // Unreachable code
bits = jumps.back().second; // Restore the number of bits we would have had left after this jump
jumps.pop_back();
prevopcode = Instruction::JUMP;
}
} else if (opcode == Instruction::JUMP) {
uint32_t jump = DecodeJump(pos, endpos);
if (jump == INVALID) return false; // Jump offset straddles EOF
if (jump > endpos - pos) return false; // Jump out of range
if (bits == 0) return false; // Consuming bits past the end of the input
--bits;
uint32_t jump_offset = pos - begin + jump;
if (!jumps.empty() && jump_offset >= jumps.back().first) return false; // Intersecting jumps
jumps.emplace_back(jump_offset, bits);
prevopcode = Instruction::JUMP;
} else if (opcode == Instruction::MATCH) {
uint32_t match = DecodeMatch(pos, endpos);
if (match == INVALID) return false; // Match bits straddle EOF
int matchlen = CountBits(match) - 1;
if (prevopcode != Instruction::MATCH) had_incomplete_match = false;
if (matchlen < 8 && had_incomplete_match) return false; // Within a sequence of matches only at most one should be incomplete
had_incomplete_match = (matchlen < 8);
if (bits < matchlen) return false; // Consuming bits past the end of the input
bits -= matchlen;
prevopcode = Instruction::MATCH;
} else if (opcode == Instruction::DEFAULT) {
if (prevopcode == Instruction::DEFAULT) return false; // There should not be two successive DEFAULTs (they could be combined into one)
uint32_t asn = DecodeASN(pos, endpos);
if (asn == INVALID) return false; // ASN straddles EOF
prevopcode = Instruction::DEFAULT;
} else {
return false; // Instruction straddles EOF
}
}
return false; // Reached EOF without RETURN instruction
}