dump: Rewrite Linux ACL handling

The old version was taken from an MPL-licensed library. This is a
cleanroom implementation. The code is shorter and it's now explicit that
only Linux ACLs are supported.

internal/dump/acl.go

@@ -1,131 +1,88 @@
 package dump
 
-// Adapted from https://github.com/maxymania/go-system/blob/master/posix_acl/posix_acl.go
-
 import (
-	"bytes"
 	"encoding/binary"
-	"fmt"
+	"errors"
+	"strconv"
 )
 
 const (
-	aclUserOwner  = 0x0001
+	// Permissions
-	aclUser       = 0x0002
+	aclPermRead    = 0x4
-	aclGroupOwner = 0x0004
+	aclPermWrite   = 0x2
-	aclGroup      = 0x0008
+	aclPermExecute = 0x1
-	aclMask       = 0x0010
+
-	aclOthers     = 0x0020
+	// Tags
+	aclTagUserObj  = 0x01 // Owner.
+	aclTagUser     = 0x02
+	aclTagGroupObj = 0x04 // Owning group.
+	aclTagGroup    = 0x08
+	aclTagMask     = 0x10
+	aclTagOther    = 0x20
 )
 
-type aclSID uint64
+// formatLinuxACL converts a Linux ACL from its binary format to the POSIX.1e
+// long text format.
+//
+// User and group IDs are printed in decimal, because we may be dumping
+// a snapshot from a different machine.
+//
+// https://man7.org/linux/man-pages/man5/acl.5.html
+// https://savannah.nongnu.org/projects/acl
+// https://simson.net/ref/1997/posix_1003.1e-990310.pdf
+func formatLinuxACL(acl []byte) (string, error) {
+	if len(acl)-4 < 0 || (len(acl)-4)%8 != 0 {
+		return "", errors.New("wrong length")
+	}
+	version := binary.LittleEndian.Uint32(acl)
+	if version != 2 {
+		return "", errors.New("unsupported ACL format version")
+	}
+	acl = acl[4:]
 
-type aclElem struct {
+	text := make([]byte, 0, 2*len(acl))
-	Tag  uint16
+
-	Perm uint16
+	for ; len(acl) >= 8; acl = acl[8:] {
-	ID   uint32
+		tag := binary.LittleEndian.Uint16(acl)
+		perm := binary.LittleEndian.Uint16(acl[2:])
+		id := binary.LittleEndian.Uint32(acl[4:])
+
+		switch tag {
+		case aclTagUserObj:
+			text = append(text, "user:"...)
+		case aclTagUser:
+			text = append(text, "user:"...)
+			text = strconv.AppendUint(text, uint64(id), 10)
+		case aclTagGroupObj:
+			text = append(text, "group:"...)
+		case aclTagGroup:
+			text = append(text, "group:"...)
+			text = strconv.AppendUint(text, uint64(id), 10)
+		case aclTagMask:
+			text = append(text, "mask:"...)
+		case aclTagOther:
+			text = append(text, "other:"...)
+		default:
+			return "", errors.New("unknown tag")
+		}
+		text = append(text, ':')
+		text = append(text, aclPermText(perm)...)
+		text = append(text, '\n')
+	}
+
+	return string(text), nil
 }
 
-type acl struct {
+func aclPermText(p uint16) []byte {
-	Version uint32
+	s := []byte("---")
-	List    []aclElement
+	if p&aclPermRead != 0 {
-}
+		s[0] = 'r'
-
+	}
-type aclElement struct {
+	if p&aclPermWrite != 0 {
-	aclSID
+		s[1] = 'w'
-	Perm uint16
+	}
-}
+	if p&aclPermExecute != 0 {
-
+		s[2] = 'x'
-func (a aclSID) getType() int {
+	}
-	return int(a >> 32)
+	return s
-}
-func (a aclSID) getID() uint32 {
-	return uint32(a & 0xffffffff)
-}
-func (a aclSID) String() string {
-	switch a >> 32 {
-	case aclUserOwner:
-		return "user::"
-	case aclUser:
-		return fmt.Sprintf("user:%v:", a.getID())
-	case aclGroupOwner:
-		return "group::"
-	case aclGroup:
-		return fmt.Sprintf("group:%v:", a.getID())
-	case aclMask:
-		return "mask::"
-	case aclOthers:
-		return "other::"
-	}
-	return "?:"
-}
-
-func (a aclElement) String() string {
-	str := ""
-	if (a.Perm & 4) != 0 {
-		str += "r"
-	} else {
-		str += "-"
-	}
-	if (a.Perm & 2) != 0 {
-		str += "w"
-	} else {
-		str += "-"
-	}
-	if (a.Perm & 1) != 0 {
-		str += "x"
-	} else {
-		str += "-"
-	}
-	return fmt.Sprintf("%v%v", a.aclSID, str)
-}
-
-func (a *acl) decode(xattr []byte) {
-	var elem aclElement
-	ae := new(aclElem)
-	nr := bytes.NewReader(xattr)
-	e := binary.Read(nr, binary.LittleEndian, &a.Version)
-	if e != nil {
-		a.Version = 0
-		return
-	}
-	if len(a.List) > 0 {
-		a.List = a.List[:0]
-	}
-	for binary.Read(nr, binary.LittleEndian, ae) == nil {
-		elem.aclSID = (aclSID(ae.Tag) << 32) | aclSID(ae.ID)
-		elem.Perm = ae.Perm
-		a.List = append(a.List, elem)
-	}
-}
-
-func (a *acl) encode() []byte {
-	buf := new(bytes.Buffer)
-	ae := new(aclElem)
-
-	err := binary.Write(buf, binary.LittleEndian, &a.Version)
-	// write to a bytes.Buffer always returns a nil error
-	if err != nil {
-		panic(err)
-	}
-
-	for _, elem := range a.List {
-		ae.Tag = uint16(elem.getType())
-		ae.Perm = elem.Perm
-		ae.ID = elem.getID()
-
-		err := binary.Write(buf, binary.LittleEndian, ae)
-		// write to a bytes.Buffer always returns a nil error
-		if err != nil {
-			panic(err)
-		}
-	}
-	return buf.Bytes()
-}
-
-func (a *acl) String() string {
-	var finalacl string
-	for _, acl := range a.List {
-		finalacl += acl.String() + "\n"
-	}
-	return finalacl
 }

internal/dump/acl_test.go

@@ -1,114 +1,46 @@
 package dump
 
 import (
-	"reflect"
 	"testing"
+
+	rtest "github.com/restic/restic/internal/test"
 )
 
-func Test_acl_decode(t *testing.T) {
+func TestFormatLinuxACL(t *testing.T) {
-	type args struct {
+	for _, c := range []struct {
-		xattr []byte
+		in, out, err string
-	}
-	tests := []struct {
-		name string
-		args args
-		want string
 	}{
 		{
-			name: "decode string",
+			in: "\x02\x00\x00\x00\x01\x00\x06\x00\xff\xff\xff\xff\x02\x00" +
-			args: args{
+				"\x04\x00\x03\x00\x00\x00\x02\x00\x04\x00\xe9\x03\x00\x00" +
-				xattr: []byte{2, 0, 0, 0, 1, 0, 6, 0, 255, 255, 255, 255, 2, 0, 7, 0, 0, 0, 0, 0, 2, 0, 7, 0, 254, 255, 0, 0, 4, 0, 7, 0, 255, 255, 255, 255, 16, 0, 7, 0, 255, 255, 255, 255, 32, 0, 4, 0, 255, 255, 255, 255},
+				"\x04\x00\x02\x00\xff\xff\xff\xff\b\x00\x01\x00'\x00\x00\x00" +
-			},
+				"\x10\x00\a\x00\xff\xff\xff\xff \x00\x04\x00\xff\xff\xff\xff",
-			want: "user::rw-\nuser:0:rwx\nuser:65534:rwx\ngroup::rwx\nmask::rwx\nother::r--\n",
+			out: "user::rw-\nuser:3:r--\nuser:1001:r--\ngroup::-w-\n" +
+				"group:39:--x\nmask::rwx\nother::r--\n",
 		},
 		{
-			name: "decode group",
+			in: "\x02\x00\x00\x00\x00\x00\x06\x00\xff\xff\xff\xff\x02\x00" +
-			args: args{
+				"\x04\x00\x03\x00\x00\x00\x02\x00\x04\x00\xe9\x03\x00\x00" +
-				xattr: []byte{2, 0, 0, 0, 8, 0, 1, 0, 254, 255, 0, 0},
+				"\x04\x00\x06\x00\xff\xff\xff\xff\b\x00\x05\x00'\x00\x00\x00" +
-			},
+				"\x10\x00\a\x00\xff\xff\xff\xff \x00\x04\x00\xff\xff\xff\xff",
-			want: "group:65534:--x\n",
+			err: "unknown tag",
 		},
 		{
-			name: "decode fail",
+			in: "\x01\x00\x00\x00\x01\x00\x06\x00\xff\xff\xff\xff\x02\x00" +
-			args: args{
+				"\x04\x00\x03\x00\x00\x00\x02\x00\x04\x00\xe9\x03\x00\x00" +
-				xattr: []byte("abctest"),
+				"\x04\x00\x06\x00\xff\xff\xff\xff\b\x00\x05\x00'\x00\x00\x00" +
-			},
+				"\x10\x00\a\x00\xff\xff\xff\xff \x00\x04\x00\xff\xff\xff\xff",
-			want: "",
+			err: "unsupported ACL format version",
-		},
-		{
-			name: "decode empty fail",
-			args: args{
-				xattr: []byte(""),
-			},
-			want: "",
 		},
+		{in: "\x02\x00", err: "wrong length"},
+		{in: "", err: "wrong length"},
+	} {
+		out, err := formatLinuxACL([]byte(c.in))
+		if c.err == "" {
+			rtest.Equals(t, c.out, out)
+		} else {
+			rtest.Assert(t, err != nil, "wanted %q but got nil", c.err)
+			rtest.Equals(t, c.err, err.Error())
 		}
-	for _, tt := range tests {
-		t.Run(tt.name, func(t *testing.T) {
-			a := &acl{}
-			a.decode(tt.args.xattr)
-			if tt.want != a.String() {
-				t.Errorf("acl.decode() = %v, want: %v", a.String(), tt.want)
-			}
-			a.decode(tt.args.xattr)
-			if tt.want != a.String() {
-				t.Errorf("second acl.decode() = %v, want: %v", a.String(), tt.want)
-			}
-		})
-	}
-}
-
-func Test_acl_encode(t *testing.T) {
-	tests := []struct {
-		name string
-		want []byte
-		args []aclElement
-	}{
-		{
-			name: "encode values",
-			want: []byte{2, 0, 0, 0, 1, 0, 6, 0, 255, 255, 255, 255, 2, 0, 7, 0, 0, 0, 0, 0, 2, 0, 7, 0, 254, 255, 0, 0, 4, 0, 7, 0, 255, 255, 255, 255, 16, 0, 7, 0, 255, 255, 255, 255, 32, 0, 4, 0, 255, 255, 255, 255},
-			args: []aclElement{
-				{
-					aclSID: 8589934591,
-					Perm:   6,
-				},
-				{
-					aclSID: 8589934592,
-					Perm:   7,
-				},
-				{
-					aclSID: 8590000126,
-					Perm:   7,
-				},
-				{
-					aclSID: 21474836479,
-					Perm:   7,
-				},
-				{
-					aclSID: 73014444031,
-					Perm:   7,
-				},
-				{
-					aclSID: 141733920767,
-					Perm:   4,
-				},
-			},
-		},
-		{
-			name: "encode fail",
-			want: []byte{2, 0, 0, 0},
-			args: []aclElement{},
-		},
-	}
-	for _, tt := range tests {
-		t.Run(tt.name, func(t *testing.T) {
-			a := &acl{
-				Version: 2,
-				List:    tt.args,
-			}
-			if got := a.encode(); !reflect.DeepEqual(got, tt.want) {
-				t.Errorf("acl.encode() = %v, want %v", got, tt.want)
-			}
-		})
 	}
 }

internal/dump/tar.go

@@ -6,8 +6,8 @@ import (
 	"fmt"
 	"os"
 	"path/filepath"
-	"strings"
 
+	"github.com/restic/restic/internal/debug"
 	"github.com/restic/restic/internal/errors"
 	"github.com/restic/restic/internal/restic"
 )
@@ -104,21 +104,28 @@ func parseXattrs(xattrs []restic.ExtendedAttribute) map[string]string {
 	tmpMap := make(map[string]string)
 
 	for _, attr := range xattrs {
-		attrString := string(attr.Value)
+		// Check for Linux POSIX.1e ACLs.
-
+		//
-		if strings.HasPrefix(attr.Name, "system.posix_acl_") {
+		// TODO support ACLs from other operating systems.
-			na := acl{}
+		// FreeBSD ACLs have names "posix1e.acl_(access|default)",
-			na.decode(attr.Value)
+		// but their binary format may not match the Linux format.
-
+		aclKey := ""
-			if na.String() != "" {
+		switch attr.Name {
-				if strings.Contains(attr.Name, "system.posix_acl_access") {
+		case "system.posix_acl_access":
-					tmpMap["SCHILY.acl.access"] = na.String()
+			aclKey = "SCHILY.acl.access"
-				} else if strings.Contains(attr.Name, "system.posix_acl_default") {
+		case "system.posix_acl_default":
-					tmpMap["SCHILY.acl.default"] = na.String()
+			aclKey = "SCHILY.acl.default"
 		}
+
+		if aclKey != "" {
+			text, err := formatLinuxACL(attr.Value)
+			if err != nil {
+				debug.Log("parsing Linux ACL: %v, skipping", err)
+				continue
 			}
+			tmpMap[aclKey] = text
 		} else {
-			tmpMap["SCHILY.xattr."+attr.Name] = attrString
+			tmpMap["SCHILY.xattr."+attr.Name] = string(attr.Value)
 		}
 	}