You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
423 lines
17 KiB
423 lines
17 KiB
package light
|
|
|
|
import (
|
|
"bytes"
|
|
"context"
|
|
"errors"
|
|
"fmt"
|
|
"time"
|
|
|
|
"github.com/tendermint/tendermint/light/provider"
|
|
"github.com/tendermint/tendermint/types"
|
|
)
|
|
|
|
// The detector component of the light client detects and handles attacks on the light client.
|
|
// More info here:
|
|
// tendermint/docs/architecture/adr-047-handling-evidence-from-light-client.md
|
|
|
|
// detectDivergence is a second wall of defense for the light client.
|
|
//
|
|
// It takes the target verified header and compares it with the headers of a set of
|
|
// witness providers that the light client is connected to. If a conflicting header
|
|
// is returned it verifies and examines the conflicting header against the verified
|
|
// trace that was produced from the primary. If successful, it produces two sets of evidence
|
|
// and sends them to the opposite provider before halting.
|
|
//
|
|
// If there are no conflictinge headers, the light client deems the verified target header
|
|
// trusted and saves it to the trusted store.
|
|
func (c *Client) detectDivergence(ctx context.Context, primaryTrace []*types.LightBlock, now time.Time) error {
|
|
if primaryTrace == nil || len(primaryTrace) < 2 {
|
|
return errors.New("nil or single block primary trace")
|
|
}
|
|
var (
|
|
headerMatched bool
|
|
lastVerifiedHeader = primaryTrace[len(primaryTrace)-1].SignedHeader
|
|
witnessesToRemove = make([]int, 0)
|
|
)
|
|
c.logger.Debug("running detector against trace", "endBlockHeight", lastVerifiedHeader.Height,
|
|
"endBlockHash", lastVerifiedHeader.Hash, "length", len(primaryTrace))
|
|
|
|
c.providerMutex.Lock()
|
|
defer c.providerMutex.Unlock()
|
|
|
|
if len(c.witnesses) == 0 {
|
|
return ErrNoWitnesses
|
|
}
|
|
|
|
// launch one goroutine per witness to retrieve the light block of the target height
|
|
// and compare it with the header from the primary
|
|
errc := make(chan error, len(c.witnesses))
|
|
for i, witness := range c.witnesses {
|
|
go c.compareNewHeaderWithWitness(ctx, errc, lastVerifiedHeader, witness, i)
|
|
}
|
|
|
|
// handle errors from the header comparisons as they come in
|
|
for i := 0; i < cap(errc); i++ {
|
|
err := <-errc
|
|
|
|
switch e := err.(type) {
|
|
case nil: // at least one header matched
|
|
headerMatched = true
|
|
case errConflictingHeaders:
|
|
// We have conflicting headers. This could possibly imply an attack on the light client.
|
|
// First we need to verify the witness's header using the same skipping verification and then we
|
|
// need to find the point that the headers diverge and examine this for any evidence of an attack.
|
|
//
|
|
// We combine these actions together, verifying the witnesses headers and outputting the trace
|
|
// which captures the bifurcation point and if successful provides the information to create valid evidence.
|
|
err := c.handleConflictingHeaders(ctx, primaryTrace, e.Block, e.WitnessIndex, now)
|
|
if err != nil {
|
|
// return information of the attack
|
|
return err
|
|
}
|
|
// if attempt to generate conflicting headers failed then remove witness
|
|
witnessesToRemove = append(witnessesToRemove, e.WitnessIndex)
|
|
|
|
case errBadWitness:
|
|
c.logger.Info("witness returned an error during header comparison, removing...",
|
|
"witness", c.witnesses[e.WitnessIndex], "err", err)
|
|
witnessesToRemove = append(witnessesToRemove, e.WitnessIndex)
|
|
default:
|
|
if errors.Is(e, context.Canceled) || errors.Is(e, context.DeadlineExceeded) {
|
|
return e
|
|
}
|
|
c.logger.Info("error in light block request to witness", "err", err)
|
|
}
|
|
}
|
|
|
|
// remove witnesses that have misbehaved
|
|
if err := c.removeWitnesses(witnessesToRemove); err != nil {
|
|
return err
|
|
}
|
|
|
|
// 1. If we had at least one witness that returned the same header then we
|
|
// conclude that we can trust the header
|
|
if headerMatched {
|
|
return nil
|
|
}
|
|
|
|
// 2. Else all witnesses have either not responded, don't have the block or sent invalid blocks.
|
|
return ErrFailedHeaderCrossReferencing
|
|
}
|
|
|
|
// compareNewHeaderWithWitness takes the verified header from the primary and compares it with a
|
|
// header from a specified witness. The function can return one of three errors:
|
|
//
|
|
// 1: errConflictingHeaders -> there may have been an attack on this light client
|
|
// 2: errBadWitness -> the witness has either not responded, doesn't have the header or has given us an invalid one
|
|
// Note: In the case of an invalid header we remove the witness
|
|
// 3: nil -> the hashes of the two headers match
|
|
func (c *Client) compareNewHeaderWithWitness(ctx context.Context, errc chan error, h *types.SignedHeader,
|
|
witness provider.Provider, witnessIndex int) {
|
|
|
|
lightBlock, err := c.getLightBlock(ctx, witness, h.Height)
|
|
switch err {
|
|
// no error means we move on to checking the hash of the two headers
|
|
case nil:
|
|
break
|
|
|
|
// the witness hasn't been helpful in comparing headers, we mark the response and continue
|
|
// comparing with the rest of the witnesses
|
|
case provider.ErrNoResponse, provider.ErrLightBlockNotFound, context.DeadlineExceeded, context.Canceled:
|
|
errc <- err
|
|
return
|
|
|
|
// the witness' head of the blockchain is lower than the height of the primary. This could be one of
|
|
// two things:
|
|
// 1) The witness is lagging behind
|
|
// 2) The primary may be performing a lunatic attack with a height and time in the future
|
|
case provider.ErrHeightTooHigh:
|
|
// The light client now asks for the latest header that the witness has
|
|
var isTargetHeight bool
|
|
isTargetHeight, lightBlock, err = c.getTargetBlockOrLatest(ctx, h.Height, witness)
|
|
if err != nil {
|
|
if c.providerShouldBeRemoved(err) {
|
|
errc <- errBadWitness{Reason: err, WitnessIndex: witnessIndex}
|
|
} else {
|
|
errc <- err
|
|
}
|
|
return
|
|
}
|
|
|
|
// if the witness caught up and has returned a block of the target height then we can
|
|
// break from this switch case and continue to verify the hashes
|
|
if isTargetHeight {
|
|
break
|
|
}
|
|
|
|
// witness' last header is below the primary's header. We check the times to see if the blocks
|
|
// have conflicting times
|
|
if !lightBlock.Time.Before(h.Time) {
|
|
errc <- errConflictingHeaders{Block: lightBlock, WitnessIndex: witnessIndex}
|
|
return
|
|
}
|
|
|
|
// the witness is behind. We wait for a period WAITING = 2 * DRIFT + LAG.
|
|
// This should give the witness ample time if it is a participating member
|
|
// of consensus to produce a block that has a time that is after the primary's
|
|
// block time. If not the witness is too far behind and the light client removes it
|
|
time.Sleep(2*c.maxClockDrift + c.maxBlockLag)
|
|
isTargetHeight, lightBlock, err = c.getTargetBlockOrLatest(ctx, h.Height, witness)
|
|
if err != nil {
|
|
if c.providerShouldBeRemoved(err) {
|
|
errc <- errBadWitness{Reason: err, WitnessIndex: witnessIndex}
|
|
} else {
|
|
errc <- err
|
|
}
|
|
return
|
|
}
|
|
if isTargetHeight {
|
|
break
|
|
}
|
|
|
|
// the witness still doesn't have a block at the height of the primary.
|
|
// Check if there is a conflicting time
|
|
if !lightBlock.Time.Before(h.Time) {
|
|
errc <- errConflictingHeaders{Block: lightBlock, WitnessIndex: witnessIndex}
|
|
return
|
|
}
|
|
|
|
// Following this request response procedure, the witness has been unable to produce a block
|
|
// that can somehow conflict with the primary's block. We thus conclude that the witness
|
|
// is too far behind and thus we return a no response error.
|
|
//
|
|
// NOTE: If the clock drift / lag has been miscalibrated it is feasible that the light client has
|
|
// drifted too far ahead for any witness to be able provide a comparable block and thus may allow
|
|
// for a malicious primary to attack it
|
|
errc <- provider.ErrNoResponse
|
|
return
|
|
|
|
default:
|
|
// all other errors (i.e. invalid block, closed connection or unreliable provider) we mark the
|
|
// witness as bad and remove it
|
|
errc <- errBadWitness{Reason: err, WitnessIndex: witnessIndex}
|
|
return
|
|
}
|
|
|
|
if !bytes.Equal(h.Header.Hash(), lightBlock.Header.Hash()) {
|
|
errc <- errConflictingHeaders{Block: lightBlock, WitnessIndex: witnessIndex}
|
|
}
|
|
|
|
c.logger.Debug("matching header received by witness", "height", h.Height, "witness", witnessIndex)
|
|
errc <- nil
|
|
}
|
|
|
|
// sendEvidence sends evidence to a provider on a best effort basis.
|
|
func (c *Client) sendEvidence(ctx context.Context, ev *types.LightClientAttackEvidence, receiver provider.Provider) {
|
|
err := receiver.ReportEvidence(ctx, ev)
|
|
if err != nil {
|
|
c.logger.Error("failed to report evidence to provider", "ev", ev, "provider", receiver)
|
|
}
|
|
}
|
|
|
|
// handleConflictingHeaders handles the primary style of attack, which is where a primary and witness have
|
|
// two headers of the same height but with different hashes
|
|
func (c *Client) handleConflictingHeaders(
|
|
ctx context.Context,
|
|
primaryTrace []*types.LightBlock,
|
|
challendingBlock *types.LightBlock,
|
|
witnessIndex int,
|
|
now time.Time,
|
|
) error {
|
|
supportingWitness := c.witnesses[witnessIndex]
|
|
witnessTrace, primaryBlock, err := c.examineConflictingHeaderAgainstTrace(
|
|
ctx,
|
|
primaryTrace,
|
|
challendingBlock,
|
|
supportingWitness,
|
|
now,
|
|
)
|
|
if err != nil {
|
|
c.logger.Info("error validating witness's divergent header", "witness", supportingWitness, "err", err)
|
|
return nil
|
|
}
|
|
|
|
// We are suspecting that the primary is faulty, hence we hold the witness as the source of truth
|
|
// and generate evidence against the primary that we can send to the witness
|
|
commonBlock, trustedBlock := witnessTrace[0], witnessTrace[len(witnessTrace)-1]
|
|
evidenceAgainstPrimary := newLightClientAttackEvidence(primaryBlock, trustedBlock, commonBlock)
|
|
c.logger.Error("ATTEMPTED ATTACK DETECTED. Sending evidence againt primary by witness", "ev", evidenceAgainstPrimary,
|
|
"primary", c.primary, "witness", supportingWitness)
|
|
c.sendEvidence(ctx, evidenceAgainstPrimary, supportingWitness)
|
|
|
|
if primaryBlock.Commit.Round != witnessTrace[len(witnessTrace)-1].Commit.Round {
|
|
c.logger.Info("The light client has detected, and prevented, an attempted amnesia attack." +
|
|
" We think this attack is pretty unlikely, so if you see it, that's interesting to us." +
|
|
" Can you let us know by opening an issue through https://github.com/tendermint/tendermint/issues/new?")
|
|
}
|
|
|
|
// This may not be valid because the witness itself is at fault. So now we reverse it, examining the
|
|
// trace provided by the witness and holding the primary as the source of truth. Note: primary may not
|
|
// respond but this is okay as we will halt anyway.
|
|
primaryTrace, witnessBlock, err := c.examineConflictingHeaderAgainstTrace(
|
|
ctx,
|
|
witnessTrace,
|
|
primaryBlock,
|
|
c.primary,
|
|
now,
|
|
)
|
|
if err != nil {
|
|
c.logger.Info("error validating primary's divergent header", "primary", c.primary, "err", err)
|
|
return ErrLightClientAttack
|
|
}
|
|
|
|
// We now use the primary trace to create evidence against the witness and send it to the primary
|
|
commonBlock, trustedBlock = primaryTrace[0], primaryTrace[len(primaryTrace)-1]
|
|
evidenceAgainstWitness := newLightClientAttackEvidence(witnessBlock, trustedBlock, commonBlock)
|
|
c.logger.Error("Sending evidence against witness by primary", "ev", evidenceAgainstWitness,
|
|
"primary", c.primary, "witness", supportingWitness)
|
|
c.sendEvidence(ctx, evidenceAgainstWitness, c.primary)
|
|
// We return the error and don't process anymore witnesses
|
|
return ErrLightClientAttack
|
|
}
|
|
|
|
// examineConflictingHeaderAgainstTrace takes a trace from one provider and a divergent header that
|
|
// it has received from another and preforms verifySkipping at the heights of each of the intermediate
|
|
// headers in the trace until it reaches the divergentHeader. 1 of 2 things can happen.
|
|
//
|
|
// 1. The light client verifies a header that is different to the intermediate header in the trace. This
|
|
// is the bifurcation point and the light client can create evidence from it
|
|
// 2. The source stops responding, doesn't have the block or sends an invalid header in which case we
|
|
// return the error and remove the witness
|
|
//
|
|
// CONTRACT:
|
|
// 1. Trace can not be empty len(trace) > 0
|
|
// 2. The last block in the trace can not be of a lower height than the target block
|
|
// trace[len(trace)-1].Height >= targetBlock.Height
|
|
// 3. The
|
|
func (c *Client) examineConflictingHeaderAgainstTrace(
|
|
ctx context.Context,
|
|
trace []*types.LightBlock,
|
|
targetBlock *types.LightBlock,
|
|
source provider.Provider, now time.Time,
|
|
) ([]*types.LightBlock, *types.LightBlock, error) {
|
|
|
|
var (
|
|
previouslyVerifiedBlock, sourceBlock *types.LightBlock
|
|
sourceTrace []*types.LightBlock
|
|
err error
|
|
)
|
|
|
|
if targetBlock.Height < trace[0].Height {
|
|
return nil, nil, fmt.Errorf("target block has a height lower than the trusted height (%d < %d)",
|
|
targetBlock.Height, trace[0].Height)
|
|
}
|
|
|
|
for idx, traceBlock := range trace {
|
|
// this case only happens in a forward lunatic attack. We treat the block with the
|
|
// height directly after the targetBlock as the divergent block
|
|
if traceBlock.Height > targetBlock.Height {
|
|
// sanity check that the time of the traceBlock is indeed less than that of the targetBlock. If the trace
|
|
// was correctly verified we should expect monotonically increasing time. This means that if the block at
|
|
// the end of the trace has a lesser time than the target block then all blocks in the trace should have a
|
|
// lesser time
|
|
if traceBlock.Time.After(targetBlock.Time) {
|
|
return nil, nil,
|
|
errors.New("sanity check failed: expected traceblock to have a lesser time than the target block")
|
|
}
|
|
|
|
// before sending back the divergent block and trace we need to ensure we have verified
|
|
// the final gap between the previouslyVerifiedBlock and the targetBlock
|
|
if previouslyVerifiedBlock.Height != targetBlock.Height {
|
|
sourceTrace, err = c.verifySkipping(ctx, source, previouslyVerifiedBlock, targetBlock, now)
|
|
if err != nil {
|
|
return nil, nil, fmt.Errorf("verifySkipping of conflicting header failed: %w", err)
|
|
}
|
|
}
|
|
return sourceTrace, traceBlock, nil
|
|
}
|
|
|
|
// get the corresponding block from the source to verify and match up against the traceBlock
|
|
if traceBlock.Height == targetBlock.Height {
|
|
sourceBlock = targetBlock
|
|
} else {
|
|
sourceBlock, err = c.getLightBlock(ctx, source, traceBlock.Height)
|
|
if err != nil {
|
|
return nil, nil, fmt.Errorf("failed to examine trace: %w", err)
|
|
}
|
|
}
|
|
|
|
// The first block in the trace MUST be the same to the light block that the source produces
|
|
// else we cannot continue with verification.
|
|
if idx == 0 {
|
|
if shash, thash := sourceBlock.Hash(), traceBlock.Hash(); !bytes.Equal(shash, thash) {
|
|
return nil, nil, fmt.Errorf("trusted block is different to the source's first block (%X = %X)",
|
|
thash, shash)
|
|
}
|
|
previouslyVerifiedBlock = sourceBlock
|
|
continue
|
|
}
|
|
|
|
// we check that the source provider can verify a block at the same height of the
|
|
// intermediate height
|
|
sourceTrace, err = c.verifySkipping(ctx, source, previouslyVerifiedBlock, sourceBlock, now)
|
|
if err != nil {
|
|
return nil, nil, fmt.Errorf("verifySkipping of conflicting header failed: %w", err)
|
|
}
|
|
// check if the headers verified by the source has diverged from the trace
|
|
if shash, thash := sourceBlock.Hash(), traceBlock.Hash(); !bytes.Equal(shash, thash) {
|
|
// Bifurcation point found!
|
|
return sourceTrace, traceBlock, nil
|
|
}
|
|
|
|
// headers are still the same. update the previouslyVerifiedBlock
|
|
previouslyVerifiedBlock = sourceBlock
|
|
}
|
|
|
|
// We have reached the end of the trace. This should never happen. This can only happen if one of the stated
|
|
// prerequisites to this function were not met. Namely that either trace[len(trace)-1].Height < targetBlock.Height
|
|
// or that trace[i].Hash() != targetBlock.Hash()
|
|
return nil, nil, errNoDivergence
|
|
|
|
}
|
|
|
|
// getTargetBlockOrLatest gets the latest height, if it is greater than the target height then it queries
|
|
// the target heght else it returns the latest. returns true if it successfully managed to acquire the target
|
|
// height.
|
|
func (c *Client) getTargetBlockOrLatest(
|
|
ctx context.Context,
|
|
height int64,
|
|
witness provider.Provider,
|
|
) (bool, *types.LightBlock, error) {
|
|
lightBlock, err := c.getLightBlock(ctx, witness, 0)
|
|
if err != nil {
|
|
return false, nil, err
|
|
}
|
|
|
|
if lightBlock.Height == height {
|
|
// the witness has caught up to the height of the provider's signed header. We
|
|
// can resume with checking the hashes.
|
|
return true, lightBlock, nil
|
|
}
|
|
|
|
if lightBlock.Height > height {
|
|
// the witness has caught up. We recursively call the function again. However in order
|
|
// to avoud a wild goose chase where the witness sends us one header below and one header
|
|
// above the height we set a timeout to the context
|
|
lightBlock, err := c.getLightBlock(ctx, witness, height)
|
|
return true, lightBlock, err
|
|
}
|
|
|
|
return false, lightBlock, nil
|
|
}
|
|
|
|
// newLightClientAttackEvidence determines the type of attack and then forms the evidence filling out
|
|
// all the fields such that it is ready to be sent to a full node.
|
|
func newLightClientAttackEvidence(conflicted, trusted, common *types.LightBlock) *types.LightClientAttackEvidence {
|
|
ev := &types.LightClientAttackEvidence{ConflictingBlock: conflicted}
|
|
// We use the common height to indicate the form of the attack.
|
|
// if this is an equivocation or amnesia attack, i.e. the validator sets are the same, then we
|
|
// return the height of the conflicting block as the common height. If instead it is a lunatic
|
|
// attack and the validator sets are not the same then we send the height of the common header.
|
|
if ev.ConflictingHeaderIsInvalid(trusted.Header) {
|
|
ev.CommonHeight = common.Height
|
|
ev.Timestamp = common.Time
|
|
ev.TotalVotingPower = common.ValidatorSet.TotalVotingPower()
|
|
} else {
|
|
ev.CommonHeight = trusted.Height
|
|
ev.Timestamp = trusted.Time
|
|
ev.TotalVotingPower = trusted.ValidatorSet.TotalVotingPower()
|
|
}
|
|
ev.ByzantineValidators = ev.GetByzantineValidators(common.ValidatorSet, trusted.SignedHeader)
|
|
return ev
|
|
}
|