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Make addrman's bucket placement deterministic.
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Give each address a single fixed location in the new and tried tables,
which become simple fixed-size arrays instead of sets and vectors.

This prevents attackers from having an advantages by inserting an
address multiple times.

This change was suggested as Countermeasure 1 in
Eclipse Attacks on Bitcoin’s Peer-to-Peer Network, Ethan Heilman,
Alison Kendler, Aviv Zohar, Sharon Goldberg. ePrint Archive Report
2015/263. March 2015.

It is also more efficient.
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@sipa
sipa committed Mar 24, 2015
1 parent b23add5 commit e6b343d
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Showing 2 changed files with 231 additions and 206 deletions.
270 changes: 124 additions & 146 deletions src/addrman.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -14,12 +14,12 @@ int CAddrInfo::GetTriedBucket(const uint256& nKey) const
{
CDataStream ss1(SER_GETHASH, 0);
std::vector<unsigned char> vchKey = GetKey();
ss1 << ((unsigned char)32) << nKey << vchKey;
ss1 << nKey << vchKey;
uint64_t hash1 = Hash(ss1.begin(), ss1.end()).GetCheapHash();

CDataStream ss2(SER_GETHASH, 0);
std::vector<unsigned char> vchGroupKey = GetGroup();
ss2 << ((unsigned char)32) << nKey << vchGroupKey << (hash1 % ADDRMAN_TRIED_BUCKETS_PER_GROUP);
ss2 << nKey << vchGroupKey << (hash1 % ADDRMAN_TRIED_BUCKETS_PER_GROUP);
uint64_t hash2 = Hash(ss2.begin(), ss2.end()).GetCheapHash();
return hash2 % ADDRMAN_TRIED_BUCKET_COUNT;
}
Expand All @@ -29,15 +29,24 @@ int CAddrInfo::GetNewBucket(const uint256& nKey, const CNetAddr& src) const
CDataStream ss1(SER_GETHASH, 0);
std::vector<unsigned char> vchGroupKey = GetGroup();
std::vector<unsigned char> vchSourceGroupKey = src.GetGroup();
ss1 << ((unsigned char)32) << nKey << vchGroupKey << vchSourceGroupKey;
ss1 << nKey << vchGroupKey << vchSourceGroupKey;
uint64_t hash1 = Hash(ss1.begin(), ss1.end()).GetCheapHash();

CDataStream ss2(SER_GETHASH, 0);
ss2 << ((unsigned char)32) << nKey << vchSourceGroupKey << (hash1 % ADDRMAN_NEW_BUCKETS_PER_SOURCE_GROUP);
ss2 << nKey << vchSourceGroupKey << (hash1 % ADDRMAN_NEW_BUCKETS_PER_SOURCE_GROUP);
uint64_t hash2 = Hash(ss2.begin(), ss2.end()).GetCheapHash();
return hash2 % ADDRMAN_NEW_BUCKET_COUNT;
}

int CAddrInfo::GetBucketPosition(const uint256 &nKey, bool fNew, int nBucket) const
{
CDataStream ss1(SER_GETHASH, 0);
std::vector<unsigned char> vchKey = GetKey();
ss1 << nKey << (fNew ? 'N' : 'K') << nBucket << vchKey;
uint64_t hash1 = Hash(ss1.begin(), ss1.end()).GetCheapHash();
return hash1 % ADDRMAN_BUCKET_SIZE;
}

bool CAddrInfo::IsTerrible(int64_t nNow) const
{
if (nLastTry && nLastTry >= nNow - 60) // never remove things tried in the last minute
Expand Down Expand Up @@ -128,130 +137,81 @@ void CAddrMan::SwapRandom(unsigned int nRndPos1, unsigned int nRndPos2)
vRandom[nRndPos2] = nId1;
}

int CAddrMan::SelectTried(int nKBucket)
void CAddrMan::Delete(int nId)
{
std::vector<int>& vTried = vvTried[nKBucket];

// randomly shuffle the first few elements (using the entire list)
// find the least recently tried among them
int64_t nOldest = -1;
int nOldestPos = -1;
for (unsigned int i = 0; i < ADDRMAN_TRIED_ENTRIES_INSPECT_ON_EVICT && i < vTried.size(); i++) {
int nPos = GetRandInt(vTried.size() - i) + i;
int nTemp = vTried[nPos];
vTried[nPos] = vTried[i];
vTried[i] = nTemp;
assert(nOldest == -1 || mapInfo.count(nTemp) == 1);
if (nOldest == -1 || mapInfo[nTemp].nLastSuccess < mapInfo[nOldest].nLastSuccess) {
nOldest = nTemp;
nOldestPos = nPos;
}
}
assert(mapInfo.count(nId) != 0);
CAddrInfo& info = mapInfo[nId];
assert(!info.fInTried);
assert(info.nRefCount == 0);

return nOldestPos;
SwapRandom(info.nRandomPos, vRandom.size() - 1);
vRandom.pop_back();
mapAddr.erase(info);
mapInfo.erase(nId);
nNew--;
}

int CAddrMan::ShrinkNew(int nUBucket)
void CAddrMan::ClearNew(int nUBucket, int nUBucketPos)
{
assert(nUBucket >= 0 && (unsigned int)nUBucket < vvNew.size());
std::set<int>& vNew = vvNew[nUBucket];

// first look for deletable items
for (std::set<int>::iterator it = vNew.begin(); it != vNew.end(); it++) {
assert(mapInfo.count(*it));
CAddrInfo& info = mapInfo[*it];
if (info.IsTerrible()) {
if (--info.nRefCount == 0) {
SwapRandom(info.nRandomPos, vRandom.size() - 1);
vRandom.pop_back();
mapAddr.erase(info);
mapInfo.erase(*it);
nNew--;
}
vNew.erase(it);
return 0;
}
}

// otherwise, select four randomly, and pick the oldest of those to replace
int n[4] = {GetRandInt(vNew.size()), GetRandInt(vNew.size()), GetRandInt(vNew.size()), GetRandInt(vNew.size())};
int nI = 0;
int nOldest = -1;
for (std::set<int>::iterator it = vNew.begin(); it != vNew.end(); it++) {
if (nI == n[0] || nI == n[1] || nI == n[2] || nI == n[3]) {
assert(nOldest == -1 || mapInfo.count(*it) == 1);
if (nOldest == -1 || mapInfo[*it].nTime < mapInfo[nOldest].nTime)
nOldest = *it;
// if there is an entry in the specified bucket, delete it.
if (vvNew[nUBucket][nUBucketPos] != -1) {
int nIdDelete = vvNew[nUBucket][nUBucketPos];
CAddrInfo& infoDelete = mapInfo[nIdDelete];
assert(infoDelete.nRefCount > 0);
infoDelete.nRefCount--;
vvNew[nUBucket][nUBucketPos] = -1;
if (infoDelete.nRefCount == 0) {
Delete(nIdDelete);
}
nI++;
}
assert(mapInfo.count(nOldest) == 1);
CAddrInfo& info = mapInfo[nOldest];
if (--info.nRefCount == 0) {
SwapRandom(info.nRandomPos, vRandom.size() - 1);
vRandom.pop_back();
mapAddr.erase(info);
mapInfo.erase(nOldest);
nNew--;
}
vNew.erase(nOldest);

return 1;
}

void CAddrMan::MakeTried(CAddrInfo& info, int nId, int nOrigin)
void CAddrMan::MakeTried(CAddrInfo& info, int nId)
{
assert(vvNew[nOrigin].count(nId) == 1);

// remove the entry from all new buckets
for (std::vector<std::set<int> >::iterator it = vvNew.begin(); it != vvNew.end(); it++) {
if ((*it).erase(nId))
for (int bucket = 0; bucket < ADDRMAN_NEW_BUCKET_COUNT; bucket++) {
int pos = info.GetBucketPosition(nKey, true, bucket);
if (vvNew[bucket][pos] == nId) {
vvNew[bucket][pos] = -1;
info.nRefCount--;
}
}
nNew--;

assert(info.nRefCount == 0);

// which tried bucket to move the entry to
int nKBucket = info.GetTriedBucket(nKey);
std::vector<int>& vTried = vvTried[nKBucket];

// first check whether there is place to just add it
if (vTried.size() < ADDRMAN_TRIED_BUCKET_SIZE) {
vTried.push_back(nId);
nTried++;
info.fInTried = true;
return;
}

// otherwise, find an item to evict
int nPos = SelectTried(nKBucket);

// find which new bucket it belongs to
assert(mapInfo.count(vTried[nPos]) == 1);
int nUBucket = mapInfo[vTried[nPos]].GetNewBucket(nKey);
std::set<int>& vNew = vvNew[nUBucket];

// remove the to-be-replaced tried entry from the tried set
CAddrInfo& infoOld = mapInfo[vTried[nPos]];
infoOld.fInTried = false;
infoOld.nRefCount = 1;
// do not update nTried, as we are going to move something else there immediately

// check whether there is place in that one,
if (vNew.size() < ADDRMAN_NEW_BUCKET_SIZE) {
// if so, move it back there
vNew.insert(vTried[nPos]);
} else {
// otherwise, move it to the new bucket nId came from (there is certainly place there)
vvNew[nOrigin].insert(vTried[nPos]);
int nKBucketPos = info.GetBucketPosition(nKey, false, nKBucket);

// first make space to add it (the existing tried entry there is moved to new, deleting whatever is there).
if (vvTried[nKBucket][nKBucketPos] != -1) {
// find an item to evict
int nIdEvict = vvTried[nKBucket][nKBucketPos];
assert(mapInfo.count(nIdEvict) == 1);
CAddrInfo& infoOld = mapInfo[nIdEvict];

// Remove the to-be-evicted item from the tried set.
infoOld.fInTried = false;
vvTried[nKBucket][nKBucketPos] = -1;
nTried--;

// find which new bucket it belongs to
int nUBucket = infoOld.GetNewBucket(nKey);
int nUBucketPos = infoOld.GetBucketPosition(nKey, true, nUBucket);
ClearNew(nUBucket, nUBucketPos);
assert(vvNew[nUBucket][nUBucketPos] == -1);

// Enter it into the new set again.
infoOld.nRefCount = 1;
vvNew[nUBucket][nUBucketPos] = nIdEvict;
nNew++;
}
nNew++;
assert(vvTried[nKBucket][nKBucketPos] == -1);

vTried[nPos] = nId;
// we just overwrote an entry in vTried; no need to update nTried
vvTried[nKBucket][nKBucketPos] = nId;
nTried++;
info.fInTried = true;
return;
}

void CAddrMan::Good_(const CService& addr, int64_t nTime)
Expand Down Expand Up @@ -281,12 +241,12 @@ void CAddrMan::Good_(const CService& addr, int64_t nTime)
return;

// find a bucket it is in now
int nRnd = GetRandInt(vvNew.size());
int nRnd = GetRandInt(ADDRMAN_NEW_BUCKET_COUNT);
int nUBucket = -1;
for (unsigned int n = 0; n < vvNew.size(); n++) {
int nB = (n + nRnd) % vvNew.size();
std::set<int>& vNew = vvNew[nB];
if (vNew.count(nId)) {
for (unsigned int n = 0; n < ADDRMAN_NEW_BUCKET_COUNT; n++) {
int nB = (n + nRnd) % ADDRMAN_NEW_BUCKET_COUNT;
int nBpos = info.GetBucketPosition(nKey, true, nB);
if (vvNew[nB][nBpos] == nId) {
nUBucket = nB;
break;
}
Expand All @@ -300,7 +260,7 @@ void CAddrMan::Good_(const CService& addr, int64_t nTime)
LogPrint("addrman", "Moving %s to tried\n", addr.ToString());

// move nId to the tried tables
MakeTried(info, nId, nUBucket);
MakeTried(info, nId);
}

bool CAddrMan::Add_(const CAddress& addr, const CNetAddr& source, int64_t nTimePenalty)
Expand Down Expand Up @@ -348,12 +308,25 @@ bool CAddrMan::Add_(const CAddress& addr, const CNetAddr& source, int64_t nTimeP
}

int nUBucket = pinfo->GetNewBucket(nKey, source);
std::set<int>& vNew = vvNew[nUBucket];
if (!vNew.count(nId)) {
pinfo->nRefCount++;
if (vNew.size() == ADDRMAN_NEW_BUCKET_SIZE)
ShrinkNew(nUBucket);
vvNew[nUBucket].insert(nId);
int nUBucketPos = pinfo->GetBucketPosition(nKey, true, nUBucket);
if (vvNew[nUBucket][nUBucketPos] != nId) {
bool fInsert = vvNew[nUBucket][nUBucketPos] == -1;
if (!fInsert) {
CAddrInfo& infoExisting = mapInfo[vvNew[nUBucket][nUBucketPos]];
if (infoExisting.IsTerrible() || (infoExisting.nRefCount > 1 && pinfo->nRefCount == 0)) {
// Overwrite the existing new table entry.
fInsert = true;
}
}
if (fInsert) {
ClearNew(nUBucket, nUBucketPos);
pinfo->nRefCount++;
vvNew[nUBucket][nUBucketPos] = nId;
} else {
if (pinfo->nRefCount == 0) {
Delete(nId);
}
}
}
return fNew;
}
Expand Down Expand Up @@ -388,13 +361,13 @@ CAddress CAddrMan::Select_(int nUnkBias)
// use a tried node
double fChanceFactor = 1.0;
while (1) {
int nKBucket = GetRandInt(vvTried.size());
std::vector<int>& vTried = vvTried[nKBucket];
if (vTried.size() == 0)
int nKBucket = GetRandInt(ADDRMAN_TRIED_BUCKET_COUNT);
int nKBucketPos = GetRandInt(ADDRMAN_BUCKET_SIZE);
if (vvTried[nKBucket][nKBucketPos] == -1)
continue;
int nPos = GetRandInt(vTried.size());
assert(mapInfo.count(vTried[nPos]) == 1);
CAddrInfo& info = mapInfo[vTried[nPos]];
int nId = vvTried[nKBucket][nKBucketPos];
assert(mapInfo.count(nId) == 1);
CAddrInfo& info = mapInfo[nId];
if (GetRandInt(1 << 30) < fChanceFactor * info.GetChance() * (1 << 30))
return info;
fChanceFactor *= 1.2;
Expand All @@ -403,16 +376,13 @@ CAddress CAddrMan::Select_(int nUnkBias)
// use a new node
double fChanceFactor = 1.0;
while (1) {
int nUBucket = GetRandInt(vvNew.size());
std::set<int>& vNew = vvNew[nUBucket];
if (vNew.size() == 0)
int nUBucket = GetRandInt(ADDRMAN_NEW_BUCKET_COUNT);
int nUBucketPos = GetRandInt(ADDRMAN_BUCKET_SIZE);
if (vvNew[nUBucket][nUBucketPos] == -1)
continue;
int nPos = GetRandInt(vNew.size());
std::set<int>::iterator it = vNew.begin();
while (nPos--)
it++;
assert(mapInfo.count(*it) == 1);
CAddrInfo& info = mapInfo[*it];
int nId = vvNew[nUBucket][nUBucketPos];
assert(mapInfo.count(nId) == 1);
CAddrInfo& info = mapInfo[nId];
if (GetRandInt(1 << 30) < fChanceFactor * info.GetChance() * (1 << 30))
return info;
fChanceFactor *= 1.2;
Expand Down Expand Up @@ -460,22 +430,30 @@ int CAddrMan::Check_()
if (mapNew.size() != nNew)
return -10;

for (int n = 0; n < vvTried.size(); n++) {
std::vector<int>& vTried = vvTried[n];
for (std::vector<int>::iterator it = vTried.begin(); it != vTried.end(); it++) {
if (!setTried.count(*it))
return -11;
setTried.erase(*it);
for (int n = 0; n < ADDRMAN_TRIED_BUCKET_COUNT; n++) {
for (int i = 0; i < ADDRMAN_BUCKET_SIZE; i++) {
if (vvTried[n][i] != -1) {
if (!setTried.count(vvTried[n][i]))
return -11;
if (mapInfo[vvTried[n][i]].GetTriedBucket(nKey) != n)
return -17;
if (mapInfo[vvTried[n][i]].GetBucketPosition(nKey, false, n) != i)
return -18;
setTried.erase(vvTried[n][i]);
}
}
}

for (int n = 0; n < vvNew.size(); n++) {
std::set<int>& vNew = vvNew[n];
for (std::set<int>::iterator it = vNew.begin(); it != vNew.end(); it++) {
if (!mapNew.count(*it))
return -12;
if (--mapNew[*it] == 0)
mapNew.erase(*it);
for (int n = 0; n < ADDRMAN_NEW_BUCKET_COUNT; n++) {
for (int i = 0; i < ADDRMAN_BUCKET_SIZE; i++) {
if (vvNew[n][i] != -1) {
if (!mapNew.count(vvNew[n][i]))
return -12;
if (mapInfo[vvNew[n][i]].GetBucketPosition(nKey, true, n) != i)
return -19;
if (--mapNew[vvNew[n][i]] == 0)
mapNew.erase(vvNew[n][i]);
}
}
}

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