passfile: directly read file instead of invoking cat

Allows better error handling, gets rid of the call to an
external program, and fixes https://github.com/rfjakob/gocryptfs/issues/278 .

10 files changed, 144 insertions, 15 deletions

diff --git a/internal/readpassword/extpass_test.go b/internal/readpassword/extpass_test.go
index b35153f..037d111 100644
--- a/internal/readpassword/extpass_test.go
+++ b/internal/readpassword/extpass_test.go
@@ -26,7 +26,7 @@ func TestExtpass(t *testing.T) {
 
 func TestOnceExtpass(t *testing.T) {
 	p1 := "lkadsf0923rdfi48rqwhdsf"
-	p2 := string(Once("echo "+p1, ""))
+	p2 := string(Once("echo "+p1, "", ""))
 	if p1 != p2 {
 		t.Errorf("p1=%q != p2=%q", p1, p2)
 	}
@@ -34,14 +34,16 @@ func TestOnceExtpass(t *testing.T) {
 
 func TestTwiceExtpass(t *testing.T) {
 	p1 := "w5w44t3wfe45srz434"
-	p2 := string(Once("echo "+p1, ""))
+	p2 := string(Once("echo "+p1, "", ""))
 	if p1 != p2 {
 		t.Errorf("p1=%q != p2=%q", p1, p2)
 	}
 }
 
 // When extpass returns an empty string, we should crash.
-// https://talks.golang.org/2014/testing.slide#23
+//
+// The TEST_SLAVE magic is explained at
+// https://talks.golang.org/2014/testing.slide#23 .
 func TestExtpassEmpty(t *testing.T) {
 	if os.Getenv("TEST_SLAVE") == "1" {
 		readPasswordExtpass("echo")
diff --git a/internal/readpassword/passfile.go b/internal/readpassword/passfile.go
new file mode 100644
index 0000000..73af279
--- /dev/null
+++ b/internal/readpassword/passfile.go
@@ -0,0 +1,43 @@
+package readpassword
+
+import (
+	"bytes"
+	"os"
+
+	"github.com/rfjakob/gocryptfs/internal/exitcodes"
+	"github.com/rfjakob/gocryptfs/internal/tlog"
+)
+
+func readPassFile(passfile string) []byte {
+	tlog.Info.Printf("passfile: reading from file %q", passfile)
+	f, err := os.Open(passfile)
+	if err != nil {
+		tlog.Fatal.Printf("fatal: passfile: could not open %q: %v", passfile, err)
+		os.Exit(exitcodes.ReadPassword)
+	}
+	defer f.Close()
+	// +1 for an optional trailing newline,
+	// +2 so we can detect if maxPasswordLen is exceeded.
+	buf := make([]byte, maxPasswordLen+2)
+	n, err := f.Read(buf)
+	if err != nil {
+		tlog.Fatal.Printf("fatal: passfile: could not read from %q: %v", passfile, err)
+		os.Exit(exitcodes.ReadPassword)
+	}
+	buf = buf[:n]
+	// Split into first line and "trailing garbage"
+	lines := bytes.SplitN(buf, []byte("\n"), 2)
+	if len(lines[0]) == 0 {
+		tlog.Fatal.Printf("fatal: passfile: empty first line in %q", passfile)
+		os.Exit(exitcodes.ReadPassword)
+	}
+	if len(lines[0]) > maxPasswordLen {
+		tlog.Fatal.Printf("fatal: passfile: max password length (%d bytes) exceeded", maxPasswordLen)
+		os.Exit(exitcodes.ReadPassword)
+	}
+	if len(lines) > 1 && len(lines[1]) > 0 {
+		tlog.Warn.Printf("passfile: ignoring trailing garbage (%d bytes) after first line",
+			len(lines[1]))
+	}
+	return lines[0]
+}
diff --git a/internal/readpassword/passfile_test.go b/internal/readpassword/passfile_test.go
new file mode 100644
index 0000000..457170b
--- /dev/null
+++ b/internal/readpassword/passfile_test.go
@@ -0,0 +1,80 @@
+package readpassword
+
+import (
+	"os"
+	"os/exec"
+	"testing"
+)
+
+func TestPassfile(t *testing.T) {
+	testcases := []struct {
+		file string
+		want string
+	}{
+		{"mypassword.txt", "mypassword"},
+		{"mypassword_garbage.txt", "mypassword"},
+		{"mypassword_missing_newline.txt", "mypassword"},
+	}
+	for _, tc := range testcases {
+		pw := readPassFile("passfile_test_files/" + tc.file)
+		if string(pw) != tc.want {
+			t.Errorf("Wrong result: want=%q have=%q", tc.want, pw)
+		}
+	}
+}
+
+// readPassFile() should exit instead of returning an empty string.
+//
+// The TEST_SLAVE magic is explained at
+// https://talks.golang.org/2014/testing.slide#23 .
+func TestPassfileEmpty(t *testing.T) {
+	if os.Getenv("TEST_SLAVE") == "1" {
+		readPassFile("passfile_test_files/empty.txt")
+		return
+	}
+	cmd := exec.Command(os.Args[0], "-test.run=TestPassfileEmpty$")
+	cmd.Env = append(os.Environ(), "TEST_SLAVE=1")
+	err := cmd.Run()
+	if err != nil {
+		return
+	}
+	t.Fatal("should have exited")
+}
+
+// File containing just a newline.
+// readPassFile() should exit instead of returning an empty string.
+//
+// The TEST_SLAVE magic is explained at
+// https://talks.golang.org/2014/testing.slide#23 .
+func TestPassfileNewline(t *testing.T) {
+	if os.Getenv("TEST_SLAVE") == "1" {
+		readPassFile("passfile_test_files/newline.txt")
+		return
+	}
+	cmd := exec.Command(os.Args[0], "-test.run=TestPassfileEmpty$")
+	cmd.Env = append(os.Environ(), "TEST_SLAVE=1")
+	err := cmd.Run()
+	if err != nil {
+		return
+	}
+	t.Fatal("should have exited")
+}
+
+// File containing "\ngarbage".
+// readPassFile() should exit instead of returning an empty string.
+//
+// The TEST_SLAVE magic is explained at
+// https://talks.golang.org/2014/testing.slide#23 .
+func TestPassfileEmptyFirstLine(t *testing.T) {
+	if os.Getenv("TEST_SLAVE") == "1" {
+		readPassFile("passfile_test_files/empty_first_line.txt")
+		return
+	}
+	cmd := exec.Command(os.Args[0], "-test.run=TestPassfileEmptyFirstLine$")
+	cmd.Env = append(os.Environ(), "TEST_SLAVE=1")
+	err := cmd.Run()
+	if err != nil {
+		return
+	}
+	t.Fatal("should have exited")
+}
diff --git a/internal/readpassword/passfile_test_files/empty.txt b/internal/readpassword/passfile_test_files/empty.txt
new file mode 100644
index 0000000..e69de29
--- /dev/null
+++ b/internal/readpassword/passfile_test_files/empty.txt
diff --git a/internal/readpassword/passfile_test_files/empty_first_line.txt b/internal/readpassword/passfile_test_files/empty_first_line.txt
new file mode 100644
index 0000000..a607e80
--- /dev/null
+++ b/internal/readpassword/passfile_test_files/empty_first_line.txt
@@ -0,0 +1,2 @@
+
+garbage
diff --git a/internal/readpassword/passfile_test_files/mypassword.txt b/internal/readpassword/passfile_test_files/mypassword.txt
new file mode 100644
index 0000000..48d23cf
--- /dev/null
+++ b/internal/readpassword/passfile_test_files/mypassword.txt
@@ -0,0 +1 @@
+mypassword
diff --git a/internal/readpassword/passfile_test_files/mypassword_garbage.txt b/internal/readpassword/passfile_test_files/mypassword_garbage.txt
new file mode 100644
index 0000000..74ba741
--- /dev/null
+++ b/internal/readpassword/passfile_test_files/mypassword_garbage.txt
@@ -0,0 +1,2 @@
+mypassword
+garbage
diff --git a/internal/readpassword/passfile_test_files/mypassword_missing_newline.txt b/internal/readpassword/passfile_test_files/mypassword_missing_newline.txt
new file mode 100644
index 0000000..b3c42b5
--- /dev/null
+++ b/internal/readpassword/passfile_test_files/mypassword_missing_newline.txt
@@ -0,0 +1 @@
+mypassword
\ No newline at end of file
diff --git a/internal/readpassword/passfile_test_files/newline.txt b/internal/readpassword/passfile_test_files/newline.txt
new file mode 100644
index 0000000..8b13789
--- /dev/null
+++ b/internal/readpassword/passfile_test_files/newline.txt
@@ -0,0 +1 @@
+
diff --git a/internal/readpassword/read.go b/internal/readpassword/read.go
index c99be5d..0378e53 100644
--- a/internal/readpassword/read.go
+++ b/internal/readpassword/read.go
@@ -24,7 +24,10 @@ const (
 
 // Once tries to get a password from the user, either from the terminal, extpass
 // or stdin. Leave "prompt" empty to use the default "Password: " prompt.
-func Once(extpass string, prompt string) []byte {
+func Once(extpass string, passfile string, prompt string) []byte {
+	if passfile != "" {
+		return readPassFile(passfile)
+	}
 	if extpass != "" {
 		return readPasswordExtpass(extpass)
 	}
@@ -39,7 +42,10 @@ func Once(extpass string, prompt string) []byte {
 
 // Twice is the same as Once but will prompt twice if we get the password from
 // the terminal.
-func Twice(extpass string) []byte {
+func Twice(extpass string, passfile string) []byte {
+	if passfile != "" {
+		return readPassFile(passfile)
+	}
 	if extpass != "" {
 		return readPasswordExtpass(extpass)
 	}
@@ -95,16 +101,7 @@ func readPasswordStdin(prompt string) []byte {
 // Exits on read error or empty result.
 func readPasswordExtpass(extpass string) []byte {
 	tlog.Info.Println("Reading password from extpass program")
-	var parts []string
-	// The option "-passfile=FILE" gets transformed to
-	// "-extpass="/bin/cat -- FILE". We don't want to split FILE on spaces,
-	// so let's handle it manually.
-	passfileCat := "/bin/cat -- "
-	if strings.HasPrefix(extpass, passfileCat) {
-		parts = []string{"/bin/cat", "--", extpass[len(passfileCat):]}
-	} else {
-		parts = strings.Split(extpass, " ")
-	}
+	parts := strings.Split(extpass, " ")
 	cmd := exec.Command(parts[0], parts[1:]...)
 	cmd.Stderr = os.Stderr
 	pipe, err := cmd.StdoutPipe()