age,cmd/age: reject oversized key files

Reported by Joe Doyle of Trail of Bits.

cmd/age/age_test.go

@@ -5,9 +5,11 @@
 package main
 
 import (
+	"io"
 	"os"
 	"os/exec"
 	"path/filepath"
+	"strings"
 	"sync"
 	"testing"
 
@@ -51,6 +53,70 @@ func (testPlugin) Unwrap(ss []*age.Stanza) ([]byte, error) {
 	return nil, age.ErrIncorrectIdentity
 }
 
+func paddedFile(pad int, lines string) io.Reader {
+	const chunkSize = 1 << 16
+	chunk := strings.Repeat("#\n", chunkSize/2)
+	var readers []io.Reader
+	if pad%2 != 0 {
+		readers = append(readers, strings.NewReader("\n"))
+		pad--
+	}
+	for ; pad > chunkSize; pad -= chunkSize {
+		readers = append(readers, strings.NewReader(chunk))
+	}
+	return io.MultiReader(append(readers,
+		strings.NewReader(chunk[:pad]), strings.NewReader(lines))...)
+}
+
+func TestParseFileSizeLimit(t *testing.T) {
+	const sizeLimit = 16 << 20
+	const identity = "AGE-SECRET-KEY-1D6K0SGAX3NU66R4GYFZY0UQWCLM3UUSF3CXLW4KXZM342WQSJ82QKU59QJ\n"
+	const recipient = "age1cy0su9fwf3gf9mw868g5yut09p6nytfmmnktexz2ya5uqg9vl9sss4euqm\n"
+	tests := []struct {
+		name  string
+		entry string
+		parse func(*testing.T, io.Reader) (int, error)
+	}{
+		{"identities", identity, func(_ *testing.T, r io.Reader) (int, error) {
+			ids, err := parseIdentities(r)
+			return len(ids), err
+		}},
+		{"recipients", recipient, func(t *testing.T, r io.Reader) (int, error) {
+			name := filepath.Join(t.TempDir(), "recipients.txt")
+			f, err := os.Create(name)
+			if err != nil {
+				t.Fatal(err)
+			}
+			if _, err := io.Copy(f, r); err != nil {
+				t.Fatal(err)
+			}
+			if err := f.Close(); err != nil {
+				t.Fatal(err)
+			}
+			recipients, err := parseRecipientsFile(name)
+			return len(recipients), err
+		}},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name+"/at limit", func(t *testing.T) {
+			r := paddedFile(sizeLimit-4*len(tt.entry), strings.Repeat(tt.entry, 4))
+			n, err := tt.parse(t, r)
+			if err != nil {
+				t.Fatal(err)
+			}
+			if n != 4 {
+				t.Errorf("got %d entries, want 4", n)
+			}
+		})
+		t.Run(tt.name+"/over limit", func(t *testing.T) {
+			r := paddedFile(sizeLimit-4*len(tt.entry), strings.Repeat(tt.entry, 8))
+			if _, err := tt.parse(t, r); err == nil {
+				t.Error("expected an error")
+			}
+		})
+	}
+}
+
 var buildExtraCommands = sync.OnceValue(func() error {
 	bindir := filepath.SplitList(os.Getenv("PATH"))[0]
 	// Build age-keygen and age-plugin-pq into the test binary directory.

cmd/age/parse.go

@@ -71,7 +71,8 @@ func parseRecipientsFile(name string) ([]age.Recipient, error) {
 	const recipientFileSizeLimit = 16 << 20 // 16 MiB
 	const lineLengthLimit = 8 << 10         // 8 KiB, same as sshd(8)
 	var recs []age.Recipient
-	scanner := bufio.NewScanner(io.LimitReader(f, recipientFileSizeLimit))
+	lr := &io.LimitedReader{R: f, N: recipientFileSizeLimit + 1}
+	scanner := bufio.NewScanner(lr)
 	var n int
 	for scanner.Scan() {
 		n++
@@ -104,6 +105,9 @@ func parseRecipientsFile(name string) ([]age.Recipient, error) {
 	if err := scanner.Err(); err != nil {
 		return nil, fmt.Errorf("%q: failed to read recipients file: %v", name, err)
 	}
+	if lr.N == 0 {
+		return nil, fmt.Errorf("%q: recipients file is too long", name)
+	}
 	if len(recs) == 0 {
 		return nil, fmt.Errorf("%q: no recipients found", name)
 	}
@@ -226,7 +230,8 @@ func parseIdentity(s string) (age.Identity, error) {
 func parseIdentities(f io.Reader) ([]age.Identity, error) {
 	const privateKeySizeLimit = 1 << 24 // 16 MiB
 	var ids []age.Identity
-	scanner := bufio.NewScanner(io.LimitReader(f, privateKeySizeLimit))
+	lr := &io.LimitedReader{R: f, N: privateKeySizeLimit + 1}
+	scanner := bufio.NewScanner(lr)
 	var n int
 	for scanner.Scan() {
 		n++
@@ -249,6 +254,9 @@ func parseIdentities(f io.Reader) ([]age.Identity, error) {
 	if err := scanner.Err(); err != nil {
 		return nil, fmt.Errorf("failed to read identities file: %v", err)
 	}
+	if lr.N == 0 {
+		return nil, fmt.Errorf("identities file is too long")
+	}
 	if len(ids) == 0 {
 		return nil, fmt.Errorf("no identities found")
 	}