Implement user manager AIDL.

This CL implements add/remove user and onPasswordChanged.
clearUID functionality, which is also part of this API will be added in
a separate upcoming CL.

Bug: 176123105
Test: TBD
Change-Id: I610441b0aac225740e09039958542dcf2f4fe0b6
diff --git a/keystore2/src/user_manager.rs b/keystore2/src/user_manager.rs
new file mode 100644
index 0000000..9ee6727
--- /dev/null
+++ b/keystore2/src/user_manager.rs
@@ -0,0 +1,94 @@
+// Copyright 2021, The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+//! This module implements IKeystoreUserManager AIDL interface.
+
+use crate::error::map_or_log_err;
+use crate::error::Error as KeystoreError;
+use crate::globals::{DB, SUPER_KEY};
+use crate::permission::KeystorePerm;
+use crate::super_key::UserState;
+use crate::utils::check_keystore_permission;
+use android_security_usermanager::aidl::android::security::usermanager::IKeystoreUserManager::{
+    BnKeystoreUserManager, IKeystoreUserManager,
+};
+use android_security_usermanager::binder::{Interface, Result as BinderResult};
+use android_system_keystore2::aidl::android::system::keystore2::ResponseCode::ResponseCode;
+use anyhow::{Context, Result};
+use binder::{IBinder, Strong};
+
+/// This struct is defined to implement the aforementioned AIDL interface.
+/// As of now, it is an empty struct.
+pub struct UserManager;
+
+impl UserManager {
+    /// Create a new instance of Keystore User Manager service.
+    pub fn new_native_binder() -> Result<Strong<dyn IKeystoreUserManager>> {
+        let result = BnKeystoreUserManager::new_binder(Self);
+        result.as_binder().set_requesting_sid(true);
+        Ok(result)
+    }
+
+    fn on_user_password_changed(user_id: i32, password: Option<&[u8]>) -> Result<()> {
+        //Check permission. Function should return if this failed. Therefore having '?' at the end
+        //is very important.
+        check_keystore_permission(KeystorePerm::change_password())
+            .context("In on_user_password_changed.")?;
+
+        match DB
+            .with(|db| {
+                UserState::get_with_password_changed(
+                    &mut db.borrow_mut(),
+                    &SUPER_KEY,
+                    user_id as u32,
+                    password,
+                )
+            })
+            .context("In on_user_password_changed.")?
+        {
+            UserState::LskfLocked => {
+                //error - password can not be changed when the device is locked
+                Err(KeystoreError::Rc(ResponseCode::LOCKED))
+                    .context("In on_user_password_changed. Device is locked.")
+            }
+            _ => {
+                //LskfLocked is the only error case for password change
+                Ok(())
+            }
+        }
+    }
+
+    fn add_or_remove_user(user_id: i32) -> Result<()> {
+        // Check permission. Function should return if this failed. Therefore having '?' at the end
+        // is very important.
+        check_keystore_permission(KeystorePerm::change_user()).context("In add_or_remove_user.")?;
+        DB.with(|db| UserState::reset_user(&mut db.borrow_mut(), &SUPER_KEY, user_id as u32, false))
+    }
+}
+
+impl Interface for UserManager {}
+
+impl IKeystoreUserManager for UserManager {
+    fn onUserPasswordChanged(&self, user_id: i32, password: Option<&[u8]>) -> BinderResult<()> {
+        map_or_log_err(Self::on_user_password_changed(user_id, password), Ok)
+    }
+
+    fn onUserAdded(&self, user_id: i32) -> BinderResult<()> {
+        map_or_log_err(Self::add_or_remove_user(user_id), Ok)
+    }
+
+    fn onUserRemoved(&self, user_id: i32) -> BinderResult<()> {
+        map_or_log_err(Self::add_or_remove_user(user_id), Ok)
+    }
+}