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hash/crc32: fix race between lazy Castagnoli init and Update/Write

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The switch on tab is checking tab == castagnoliTable,
but castagnoliTable can change value during a concurrent
call to MakeTable.

Fixes #41911.

Change-Id: I6124dcdbf33e17fe302baa3e1aa03202dec61b4c
Reviewed-on: https://go-review.googlesource.com/c/go/+/261639
Trust: Russ Cox <rsc@golang.org>
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
This commit is contained in:
Russ Cox 2020-10-12 15:41:14 -04:00
parent 7bda6154ca
commit 5ef78c4d84
2 changed files with 20 additions and 6 deletions
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16
src/hash/crc32/crc32.go
View File

@ -16,6 +16,7 @@ import (
"errors"
"hash"
"sync"
"sync/atomic"
)
// The size of a CRC-32 checksum in bytes.
@ -78,6 +79,7 @@ var castagnoliTable8 *slicing8Table
var castagnoliArchImpl bool
var updateCastagnoli func(crc uint32, p []byte) uint32
var castagnoliOnce sync.Once
var haveCastagnoli uint32
func castagnoliInit() {
castagnoliTable = simpleMakeTable(Castagnoli)
@ -93,6 +95,8 @@ func castagnoliInit() {
return slicingUpdate(crc, castagnoliTable8, p)
}
}
atomic.StoreUint32(&haveCastagnoli, 1)
}
// IEEETable is the table for the IEEE polynomial.
@ -208,10 +212,10 @@ func readUint32(b []byte) uint32 {
// Update returns the result of adding the bytes in p to the crc.
func Update(crc uint32, tab *Table, p []byte) uint32 {
switch tab {
case castagnoliTable:
switch {
case atomic.LoadUint32(&haveCastagnoli) != 0 && tab == castagnoliTable:
return updateCastagnoli(crc, p)
case IEEETable:
case tab == IEEETable:
// Unfortunately, because IEEETable is exported, IEEE may be used without a
// call to MakeTable. We have to make sure it gets initialized in that case.
ieeeOnce.Do(ieeeInit)
@ -222,10 +226,10 @@ func Update(crc uint32, tab *Table, p []byte) uint32 {
}
func (d *digest) Write(p []byte) (n int, err error) {
switch d.tab {
case castagnoliTable:
switch {
case atomic.LoadUint32(&haveCastagnoli) != 0 && d.tab == castagnoliTable:
d.crc = updateCastagnoli(d.crc, p)
case IEEETable:
case d.tab == IEEETable:
// We only create digest objects through New() which takes care of
// initialization in this case.
d.crc = updateIEEE(d.crc, p)

10
src/hash/crc32/crc32_test.go
View File

@ -13,6 +13,16 @@ import (
"testing"
)
// First test, so that it can be the one to initialize castagnoliTable.
func TestCastagnoliRace(t *testing.T) {
// The MakeTable(Castagnoli) lazily initializes castagnoliTable,
// which races with the switch on tab during Write to check
// whether tab == castagnoliTable.
ieee := NewIEEE()
go MakeTable(Castagnoli)
ieee.Write([]byte("hello"))
}
type test struct {
ieee, castagnoli uint32
in string