No password: Use `*` instead of `!`. (#6668)

toolkit/tools/internal/userutils/userutils.go

@@ -93,8 +93,14 @@ func UpdateUserPassword(installRoot, username, hashedPassword string) error {
 	shadowFilePath := filepath.Join(installRoot, ShadowFile)
 
 	if hashedPassword == "" {
-		// In the /etc/shadow file, `!` means there is no password and password login is disabled.
-		hashedPassword = "!"
+		// In the /etc/shadow file, the values `*` and `!` both mean the user's password login is disabled but the user
+		// may login using other means (e.g. ssh, auto-login, etc.). This interpretation is also used by PAM. When sshd
+		// has `UsePAM` set to `yes`, then sshd defers to PAM the decision on whether or not the user is disabled.
+		// However, when `UsePAM` is set to `no`, then sshd must make this interpretation for itself. And the Mariner
+		// build of sshd is configured to interpret the `!` in the shadow file to mean the user is fully disabled, even
+		// for ssh login. But it interprets `*` to mean that only password login is disabled but sshd public/private key
+		// login is fine.
+		hashedPassword = "*"
 	}
 
 	// Find the line that starts with "<user>:<password>:..."

toolkit/tools/internal/userutils/userutils_test.go

@@ -80,20 +80,20 @@ func TestHashPasswordNotEmpty(t *testing.T) {
 }
 
 func TestUpdateUserPasswordEmptyToEmpty(t *testing.T) {
-	testUpdateUserPassword(t, "root:!:19634:7:99999:7:::", "root:!:19634:7:99999:7:::", "root", "")
+	testUpdateUserPassword(t, "root:*:19634:7:99999:7:::", "root:*:19634:7:99999:7:::", "root", "")
 }
 
 func TestUpdateUserPasswordSomethingToEmpty(t *testing.T) {
 	testUpdateUserPassword(t,
 		"root:$6$E0M9VkDvOLvO$nr9FjmIiSSP5C5V3Lhuqv4VzWmscABoiQ0mF.ZTbwKEN4nS60nsiU17qA/RGMbXHtJfci/DeLT1Zu2nhNFbwQ.:19634:7:99999:7:::",
-		"root:!:19634:7:99999:7:::",
+		"root:*:19634:7:99999:7:::",
 		"root",
 		"")
 }
 
 func TestUpdateUserPassword(t *testing.T) {
 	testUpdateUserPassword(t,
-		"root:!:19634:7:99999:7:::",
+		"root:*:19634:7:99999:7:::",
 		"root:$6$E0M9VkDvOLvO$nr9FjmIiSSP5C5V3Lhuqv4VzWmscABoiQ0mF.ZTbwKEN4nS60nsiU17qA/RGMbXHtJfci/DeLT1Zu2nhNFbwQ.:19634:7:99999:7:::",
 		"root",
 		"$6$E0M9VkDvOLvO$nr9FjmIiSSP5C5V3Lhuqv4VzWmscABoiQ0mF.ZTbwKEN4nS60nsiU17qA/RGMbXHtJfci/DeLT1Zu2nhNFbwQ.")