Don't overwrite shell when updating user entry

internal/users/db/db_test.go

@@ -144,6 +144,13 @@ func TestUpdateUserEntry(t *testing.T) {
 			Dir:   "/new/home/user1",
 			Shell: "/bin/bash",
 		},
+		"user1-new-shell": {
+			Name:  "user1",
+			UID:   1111,
+			Gecos: "User1 gecos\nOn multiple lines",
+			Dir:   "/new/home/user1",
+			Shell: "/new/shell",
+		},
 		"user1-without-gecos": {
 			Name:  "user1",
 			UID:   1111,
@@ -185,6 +192,7 @@ func TestUpdateUserEntry(t *testing.T) {
 		// User and Group updates
 		"Update_user_by_changing_attributes":                      {userCase: "user1-new-attributes", dbFile: "one_user_and_group"},
 		"Update_user_does_not_change_homedir_if_it_exists":        {userCase: "user1-new-homedir", dbFile: "one_user_and_group"},
+		"Update_user_does_not_change_shell_if_it_exists":          {userCase: "user1-new-shell", dbFile: "one_user_and_group"},
 		"Update_user_by_removing_optional_gecos_field_if_not_set": {userCase: "user1-without-gecos", dbFile: "one_user_and_group"},
 
 		// Group updates

internal/users/db/testdata/golden/TestUpdateUserEntry/Update_user_by_changing_attributes

@@ -4,7 +4,7 @@ users:
       gid: 11111
       gecos: New user1 gecos
       dir: /home/user1
-      shell: /bin/dash
+      shell: /bin/bash
 groups:
     - name: group1
       gid: 11111

internal/users/db/testdata/golden/TestUpdateUserEntry/Update_user_does_not_change_shell_if_it_exists

@@ -0,0 +1,16 @@
+users:
+    - name: user1
+      uid: 1111
+      gid: 11111
+      gecos: |-
+        User1 gecos
+        On multiple lines
+      dir: /home/user1
+      shell: /bin/bash
+groups:
+    - name: group1
+      gid: 11111
+      ugid: "12345678"
+users_to_groups:
+    - uid: 1111
+      gid: 11111

internal/users/db/update.go

@@ -47,6 +47,8 @@ func (m *Manager) UpdateUserEntry(user UserRow, authdGroups []GroupRow, localGro
 
 // handleUserUpdate updates the user record in the database.
 func handleUserUpdate(db queryable, u UserRow) error {
+	log.Debugf(context.Background(), "Updating entry of user %q (UID: %d)", u.Name, u.UID)
+
 	existingUser, err := userByID(db, u.UID)
 	if err != nil && !errors.Is(err, NoDataFoundError{}) {
 		return err
@@ -64,7 +66,12 @@ func handleUserUpdate(db queryable, u UserRow) error {
 		u.Dir = existingUser.Dir
 	}
 
-	log.Debugf(context.Background(), "Updating entry of user %q (UID: %d)", u.Name, u.UID)
+	// Ensure that we use the same shell as the one we have in the database.
+	if existingUser.Shell != "" && existingUser.Shell != u.Shell {
+		log.Debugf(context.TODO(), "Not updating shell to %q because it's already set to %q", u.Shell, existingUser.Shell)
+		u.Shell = existingUser.Shell
+	}
+
 	return insertOrUpdateUserByID(db, u)
 }