internal/coverage: use 128-bit FNV-1a hash instead of MD5

This change replaces the MD5 hash used to identify coverage files with a
128-bit FNV-1a hash. This change is motivated by the fact that MD5
should only be used for legacy cryptographic purposes.

The 128-bit FNV-1a hash is sufficient for the purpose of identifying
coverage files, it having the same theoretical collision resistance as
MD5, but with the added benefit of being faster to compute.

Change-Id: I7b547ce2ea784f8f4071599a10fcb512b87ee469
Reviewed-on: https://go-review.googlesource.com/c/go/+/617360
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Than McIntosh <thanm@golang.org>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>

diff --git a/src/cmd/covdata/metamerge.go b/src/cmd/covdata/metamerge.go
index bf088b11366ea602a04ba6fd1fb76943c655265d..b3c62460e466c8af025fd194e2f2e755d6c7d3b0 100644 (file)
--- a/src/cmd/covdata/metamerge.go
+++ b/src/cmd/covdata/metamerge.go
@@ -9,8 +9,8 @@ package main
 // and "intersect" subcommands.
 
 import (
-       "crypto/md5"
        "fmt"
+       "hash/fnv"
        "internal/coverage"
        "internal/coverage/calloc"
        "internal/coverage/cmerge"
@@ -207,7 +207,8 @@ func (mm *metaMerge) endPod(pcombine bool) {
 // part of a merge operation, specifically a merge with the
 // "-pcombine" flag.
 func (mm *metaMerge) emitMeta(outdir string, pcombine bool) [16]byte {
-       fh := md5.New()
+       fh := fnv.New128a()
+       fhSum := fnv.New128a()
        blobs := [][]byte{}
        tlen := uint64(unsafe.Sizeof(coverage.MetaFileHeader{}))
        for _, p := range mm.pkgs {
@@ -219,7 +220,9 @@ func (mm *metaMerge) emitMeta(outdir string, pcombine bool) [16]byte {
                } else {
                        blob = p.mdblob
                }
-               ph := md5.Sum(blob)
+               fhSum.Reset()
+               fhSum.Write(blob)
+               ph := fhSum.Sum(nil)
                blobs = append(blobs, blob)
                if _, err := fh.Write(ph[:]); err != nil {
                        panic(fmt.Sprintf("internal error: md5 sum failed: %v", err))

diff --git a/src/go/build/deps_test.go b/src/go/build/deps_test.go
index 6545dd421dfe7ededfa3cac43842c764affac04b..3adc26ae2b6e299d01765e05668f1a9b514556ee 100644 (file)
--- a/src/go/build/deps_test.go
+++ b/src/go/build/deps_test.go
@@ -685,7 +685,7 @@ var depsRules = `
        < internal/trace/traceviewer;
 
        # Coverage.
-       FMT, crypto/md5, encoding/binary, regexp, sort, text/tabwriter,
+       FMT, hash/fnv, encoding/binary, regexp, sort, text/tabwriter,
        internal/coverage, internal/coverage/uleb128
        < internal/coverage/cmerge,
          internal/coverage/pods,

diff --git a/src/internal/coverage/cfile/emit.go b/src/internal/coverage/cfile/emit.go
index 3993e9cb4247e9e6d678fc05b319e8f3fab13e0a..47de7778b0b24f4bf543075aae0a5b316a9ab995 100644 (file)
--- a/src/internal/coverage/cfile/emit.go
+++ b/src/internal/coverage/cfile/emit.go
@@ -9,8 +9,8 @@
 package cfile
 
 import (
-       "crypto/md5"
        "fmt"
+       "hash/fnv"
        "internal/coverage"
        "internal/coverage/encodecounter"
        "internal/coverage/encodemeta"
@@ -206,7 +206,7 @@ func prepareForMetaEmit() ([]rtcov.CovMetaBlob, error) {
                }
        }
 
-       h := md5.New()
+       h := fnv.New128a()
        tlen := uint64(unsafe.Sizeof(coverage.MetaFileHeader{}))
        for _, entry := range ml {
                if _, err := h.Write(entry.Hash[:]); err != nil {

diff --git a/src/internal/coverage/decodemeta/decodefile.go b/src/internal/coverage/decodemeta/decodefile.go
index 96e076596f8bf5d850bd95aa6f87841ea3a247ad..6f4dd1a3ec0c74c77735f698b8f4595074be26d9 100644 (file)
--- a/src/internal/coverage/decodemeta/decodefile.go
+++ b/src/internal/coverage/decodemeta/decodefile.go
@@ -12,9 +12,9 @@ package decodemeta
 
 import (
        "bufio"
-       "crypto/md5"
        "encoding/binary"
        "fmt"
+       "hash/fnv"
        "internal/coverage"
        "internal/coverage/slicereader"
        "internal/coverage/stringtab"
@@ -171,8 +171,10 @@ func (r *CoverageMetaFileReader) FileHash() [16]byte {
 func (r *CoverageMetaFileReader) GetPackageDecoder(pkIdx uint32, payloadbuf []byte) (*CoverageMetaDataDecoder, []byte, error) {
        pp, err := r.GetPackagePayload(pkIdx, payloadbuf)
        if r.debug {
+               h := fnv.New128a()
+               h.Write(pp)
                fmt.Fprintf(os.Stderr, "=-= pkidx=%d payload length is %d hash=%s\n",
-                       pkIdx, len(pp), fmt.Sprintf("%x", md5.Sum(pp)))
+                       pkIdx, len(pp), fmt.Sprintf("%x", h.Sum(nil)))
        }
        if err != nil {
                return nil, nil, err

diff --git a/src/internal/coverage/encodemeta/encode.go b/src/internal/coverage/encodemeta/encode.go
index 549b3f55a8e304cc05c73b631142822310f64d92..e8f70fe575ad1efe1eaa69d192d20d4a356a2dcc 100644 (file)
--- a/src/internal/coverage/encodemeta/encode.go
+++ b/src/internal/coverage/encodemeta/encode.go
@@ -10,10 +10,10 @@ package encodemeta
 
 import (
        "bytes"
-       "crypto/md5"
        "encoding/binary"
        "fmt"
        "hash"
+       "hash/fnv"
        "internal/coverage"
        "internal/coverage/stringtab"
        "internal/coverage/uleb128"
@@ -39,7 +39,7 @@ func NewCoverageMetaDataBuilder(pkgpath string, pkgname string, modulepath strin
        }
        x := &CoverageMetaDataBuilder{
                tmp: make([]byte, 0, 256),
-               h:   md5.New(),
+               h:   fnv.New128a(),
        }
        x.stab.InitWriter()
        x.stab.Lookup("")
@@ -188,7 +188,7 @@ func (b *CoverageMetaDataBuilder) Emit(w io.WriteSeeker) ([16]byte, error) {
 // HashFuncDesc computes an md5 sum of a coverage.FuncDesc and returns
 // a digest for it.
 func HashFuncDesc(f *coverage.FuncDesc) [16]byte {
-       h := md5.New()
+       h := fnv.New128a()
        tmp := make([]byte, 0, 32)
        hashFuncDesc(h, f, tmp)
        var r [16]byte

diff --git a/src/internal/coverage/encodemeta/encodefile.go b/src/internal/coverage/encodemeta/encodefile.go
index 38ae46e4f5617f6609039cfb38855364e10e2df6..ae7c23ad976216570d08ba2966a6fce3fbf59002 100644 (file)
--- a/src/internal/coverage/encodemeta/encodefile.go
+++ b/src/internal/coverage/encodemeta/encodefile.go
@@ -6,9 +6,9 @@ package encodemeta
 
 import (
        "bufio"
-       "crypto/md5"
        "encoding/binary"
        "fmt"
+       "hash/fnv"
        "internal/coverage"
        "internal/coverage/stringtab"
        "io"
@@ -112,7 +112,9 @@ func (m *CoverageMetaFileWriter) Write(finalHash [16]byte, blobs [][]byte, mode
        // Now emit blobs themselves.
        for k, blob := range blobs {
                if m.debug {
-                       fmt.Fprintf(os.Stderr, "=+= writing blob %d len %d at off=%d hash %s\n", k, len(blob), off2, fmt.Sprintf("%x", md5.Sum(blob)))
+                       h := fnv.New128a()
+                       h.Write(blob)
+                       fmt.Fprintf(os.Stderr, "=+= writing blob %d len %d at off=%d hash %s\n", k, len(blob), off2, fmt.Sprintf("%x", h.Sum(nil)))
                }
                if _, err = m.w.Write(blob); err != nil {
                        return fmt.Errorf("error writing %s: %v", m.mfname, err)

diff --git a/src/internal/coverage/pods/pods_test.go b/src/internal/coverage/pods/pods_test.go
index 69c16e00eb01d41a8308f32cbab211451261b6c6..eed01698e27a5544f151a7708de4a9260e347999 100644 (file)
--- a/src/internal/coverage/pods/pods_test.go
+++ b/src/internal/coverage/pods/pods_test.go
@@ -5,8 +5,8 @@
 package pods_test
 
 import (
-       "crypto/md5"
        "fmt"
+       "hash/fnv"
        "internal/coverage"
        "internal/coverage/pods"
        "os"
@@ -35,13 +35,17 @@ func TestPodCollection(t *testing.T) {
        }
 
        mkmeta := func(dir string, tag string) string {
-               hash := md5.Sum([]byte(tag))
+               h := fnv.New128a()
+               h.Write([]byte(tag))
+               hash := h.Sum(nil)
                fn := fmt.Sprintf("%s.%x", coverage.MetaFilePref, hash)
                return mkfile(dir, fn)
        }
 
        mkcounter := func(dir string, tag string, nt int, pid int) string {
-               hash := md5.Sum([]byte(tag))
+               h := fnv.New128a()
+               h.Write([]byte(tag))
+               hash := h.Sum(nil)
                fn := fmt.Sprintf(coverage.CounterFileTempl, coverage.CounterFilePref, hash, pid, nt)
                return mkfile(dir, fn)
        }
@@ -112,16 +116,16 @@ func TestPodCollection(t *testing.T) {
        }
 
        expected := []string{
-               `o1/covmeta.ae7be26cdaa742ca148068d5ac90eaca [
-o1/covcounters.ae7be26cdaa742ca148068d5ac90eaca.40.2 o:0
-o1/covcounters.ae7be26cdaa742ca148068d5ac90eaca.41.2 o:0
-o1/covcounters.ae7be26cdaa742ca148068d5ac90eaca.42.1 o:0
-o2/covcounters.ae7be26cdaa742ca148068d5ac90eaca.35.11 o:1
+               `o1/covmeta.0880952782ab1be95aa0733055a4d06b [
+o1/covcounters.0880952782ab1be95aa0733055a4d06b.40.2 o:0
+o1/covcounters.0880952782ab1be95aa0733055a4d06b.41.2 o:0
+o1/covcounters.0880952782ab1be95aa0733055a4d06b.42.1 o:0
+o2/covcounters.0880952782ab1be95aa0733055a4d06b.35.11 o:1
 ]`,
-               `o2/covmeta.aaf2f89992379705dac844c0a2a1d45f [
-o2/covcounters.aaf2f89992379705dac844c0a2a1d45f.36.3 o:1
-o2/covcounters.aaf2f89992379705dac844c0a2a1d45f.37.2 o:1
-o2/covcounters.aaf2f89992379705dac844c0a2a1d45f.38.1 o:1
+               `o2/covmeta.0880952783ab1be95aa0733055a4d1a6 [
+o2/covcounters.0880952783ab1be95aa0733055a4d1a6.36.3 o:1
+o2/covcounters.0880952783ab1be95aa0733055a4d1a6.37.2 o:1
+o2/covcounters.0880952783ab1be95aa0733055a4d1a6.38.1 o:1
 ]`,
        }
        for k, exp := range expected {