Check for trailing garbage after the password

From the comment:

// CheckTrailingGarbage tries to read one byte from stdin and exits with a
// fatal error if the read returns any data.
// This is meant to be called after reading the password, when there is no more
// data expected. This helps to catch problems with third-party tools that
// interface with gocryptfs.

1 files changed, 32 insertions, 0 deletions

diff --git a/internal/readpassword/read.go b/internal/readpassword/read.go
index 49cf8ef..fe9be45 100644
--- a/internal/readpassword/read.go
+++ b/internal/readpassword/read.go
@@ -7,6 +7,8 @@ import (
 	"os"
 	"os/exec"
 	"strings"
+	"sync"
+	"time"
 
 	"golang.org/x/crypto/ssh/terminal"
 
@@ -141,3 +143,33 @@ func readLineUnbuffered(r io.Reader) (l string) {
 		l = l + string(b)
 	}
 }
+
+// CheckTrailingGarbage tries to read one byte from stdin and exits with a
+// fatal error if the read returns any data.
+// This is meant to be called after reading the password, when there is no more
+// data expected. This helps to catch problems with third-party tools that
+// interface with gocryptfs.
+//
+// This is tested via TestInitTrailingGarbage() in tests/cli/cli_test.go.
+func CheckTrailingGarbage() {
+	if terminal.IsTerminal(int(os.Stdin.Fd())) {
+		// Be lenient when interacting with a human.
+		return
+	}
+	var wg sync.WaitGroup
+	wg.Add(1)
+	go func() {
+		b := make([]byte, 1)
+		wg.Done()
+		n, _ := os.Stdin.Read(b)
+		if n > 0 {
+			tlog.Fatal.Printf("Received trailing garbage after the password")
+			os.Exit(exitCode)
+		}
+	}()
+	// Wait for the goroutine to start up plus one millisecond for the read to
+	// return. If there is data available, this SHOULD be plenty of time to
+	// read one byte. However, I don't see a way to be sure.
+	wg.Wait()
+	time.Sleep(1 * time.Millisecond)
+}