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Merge pull request #3519 from greatroar/maphash

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Replace siphash by hash/maphash
This commit is contained in:
MichaelEischer
2021-09-19 19:46:03 +02:00
committed by GitHub
parent 58efe21eca 8b758c78a3
commit 1827b16ade
9 changed files with 19 additions and 63 deletions
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22
internal/repository/indexmap.go
View File

@@ -1,12 +1,9 @@
package repository
import (
"crypto/rand"
"encoding/binary"
"hash/maphash"
"github.com/restic/restic/internal/restic"
"github.com/dchest/siphash"
)
// An indexMap is a chained hash table that maps blob IDs to indexEntries.
@@ -23,7 +20,7 @@ type indexMap struct {
buckets []*indexEntry
numentries uint
key0, key1 uint64 // Key for hash randomization.
mh maphash.Hash
free *indexEntry // Free list.
}
@@ -113,25 +110,20 @@ func (m *indexMap) grow() {
}
func (m *indexMap) hash(id restic.ID) uint {
// We use siphash with a randomly generated 128-bit key, to prevent
// backups of specially crafted inputs from degrading performance.
// We use maphash to prevent backups of specially crafted inputs
// from degrading performance.
// While SHA-256 should be collision-resistant, for hash table indices
// we use only a few bits of it and finding collisions for those is
// much easier than breaking the whole algorithm.
h := uint(siphash.Hash(m.key0, m.key1, id[:]))
m.mh.Reset()
_, _ = m.mh.Write(id[:])
h := uint(m.mh.Sum64())
return h & uint(len(m.buckets)-1)
}
func (m *indexMap) init() {
const initialBuckets = 64
m.buckets = make([]*indexEntry, initialBuckets)
var buf [16]byte
if _, err := rand.Read(buf[:]); err != nil {
panic(err) // Very little we can do here.
}
m.key0 = binary.LittleEndian.Uint64(buf[:8])
m.key1 = binary.LittleEndian.Uint64(buf[8:])
}
func (m *indexMap) len() uint { return m.numentries }

26
internal/repository/indexmap_test.go
View File

@@ -107,32 +107,6 @@ func TestIndexMapForeachWithID(t *testing.T) {
}
}
func TestIndexMapHash(t *testing.T) {
t.Parallel()
var m1, m2 indexMap
id := restic.NewRandomID()
// Add to both maps to initialize them.
m1.add(id, 0, 0, 0)
m2.add(id, 0, 0, 0)
h1 := m1.hash(id)
h2 := m2.hash(id)
rtest.Equals(t, len(m1.buckets), len(m2.buckets)) // just to be sure
if h1 == h2 {
// The probability of the zero key should be 2^(-128).
if m1.key0 == 0 && m1.key1 == 0 {
t.Error("siphash key not set for m1")
}
if m2.key0 == 0 && m2.key1 == 0 {
t.Error("siphash key not set for m2")
}
}
}
func BenchmarkIndexMapHash(b *testing.B) {
var m indexMap
m.add(restic.ID{}, 0, 0, 0) // Trigger lazy initialization.