fix: correctly handle degenerate hamts while reading data

Fixes GHSA-q264-w97q-q778

Author: Jorropo

go.mod

@@ -3,7 +3,7 @@ module github.com/ipfs/go-unixfs
 require (
 	github.com/alecthomas/units v0.0.0-20210927113745-59d0afb8317a
 	github.com/gogo/protobuf v1.3.2
-	github.com/ipfs/go-bitfield v1.0.0
+	github.com/ipfs/go-bitfield v1.1.0
 	github.com/ipfs/go-block-format v0.0.3
 	github.com/ipfs/go-blockservice v0.2.1
 	github.com/ipfs/go-cid v0.3.2

go.sum

@@ -244,8 +244,8 @@ github.com/inconshreveable/mousetrap v1.0.0/go.mod h1:PxqpIevigyE2G7u3NXJIT2ANyt
 github.com/influxdata/influxdb1-client v0.0.0-20191209144304-8bf82d3c094d/go.mod h1:qj24IKcXYK6Iy9ceXlo3Tc+vtHo9lIhSX5JddghvEPo=
 github.com/ipfs/bbloom v0.0.4 h1:Gi+8EGJ2y5qiD5FbsbpX/TMNcJw8gSqr7eyjHa4Fhvs=
 github.com/ipfs/bbloom v0.0.4/go.mod h1:cS9YprKXpoZ9lT0n/Mw/a6/aFV6DTjTLYHeA+gyqMG0=
-github.com/ipfs/go-bitfield v1.0.0 h1:y/XHm2GEmD9wKngheWNNCNL0pzrWXZwCdQGv1ikXknQ=
-github.com/ipfs/go-bitfield v1.0.0/go.mod h1:N/UiujQy+K+ceU1EF5EkVd1TNqevLrCQMIcAEPrdtus=
+github.com/ipfs/go-bitfield v1.1.0 h1:fh7FIo8bSwaJEh6DdTWbCeZ1eqOaOkKFI74SCnsWbGA=
+github.com/ipfs/go-bitfield v1.1.0/go.mod h1:paqf1wjq/D2BBmzfTVFlJQ9IlFOZpg422HL0HqsGWHU=
 github.com/ipfs/go-bitswap v0.5.1 h1:721YAEDBnLIrvcIMkCHCdqp34hA8jwL9yKMkyJpSpco=
 github.com/ipfs/go-bitswap v0.5.1/go.mod h1:P+ckC87ri1xFLvk74NlXdP0Kj9RmWAh4+H78sC6Qopo=
 github.com/ipfs/go-block-format v0.0.2/go.mod h1:AWR46JfpcObNfg3ok2JHDUfdiHRgWhJgCQF+KIgOPJY=

hamt/hamt.go

@@ -106,12 +106,16 @@ func makeShard(ds ipld.DAGService, size int, key string, val *ipld.Link) (*Shard
 	if err != nil {
 		return nil, err
 	}
+	childer, err := newChilder(ds, size)
+	if err != nil {
+		return nil, err
+	}
 	maxpadding := fmt.Sprintf("%X", size-1)
 	s := &Shard{
 		tableSizeLg2: lg2s,
 		prefixPadStr: fmt.Sprintf("%%0%dX", len(maxpadding)),
 		maxpadlen:    len(maxpadding),
-		childer:      newChilder(ds, size),
+		childer:      childer,
 		tableSize:    size,
 		dserv:        ds,
 
@@ -765,11 +769,21 @@ type childer struct {
 	children []*Shard
 }
 
-func newChilder(ds ipld.DAGService, size int) *childer {
+const maximumHamtWidth = 1 << 10 // FIXME: Spec this and decide of a correct value
+
+func newChilder(ds ipld.DAGService, size int) (*childer, error) {
+	if size > maximumHamtWidth {
+		return nil, fmt.Errorf("hamt witdh (%d) exceed maximum allowed (%d)", size, maximumHamtWidth)
+	}
+	bf, err := bitfield.NewBitfield(size)
+	if err != nil {
+		return nil, err
+	}
+
 	return &childer{
 		dserv:    ds,
-		bitfield: bitfield.NewBitfield(size),
-	}
+		bitfield: bf,
+	}, nil
 }
 
 func (s *childer) makeChilder(data []byte, links []*ipld.Link) *childer {

hamt/hamt_test.go

@@ -737,8 +737,10 @@ func BenchmarkHAMTSet(b *testing.B) {
 }
 
 func TestHamtBadSize(t *testing.T) {
-	_, err := NewShard(nil, 7)
-	if err == nil {
-		t.Fatal("should have failed to construct hamt with bad size")
+	for _, size := range [...]int{-8, 7, 2, 1337, 1024 + 8, -3} {
+		_, err := NewShard(nil, size)
+		if err == nil {
+			t.Error("should have failed to construct hamt with bad size: %d", size)
+		}
 	}
 }