Add experimental and preliminary policy-driven session limiting when logging in compatibility sessions.

crates/cli/src/util.rs

@@ -145,6 +145,7 @@ pub async fn policy_factory_from_config(
         register: config.register_entrypoint.clone(),
         client_registration: config.client_registration_entrypoint.clone(),
         authorization_grant: config.authorization_grant_entrypoint.clone(),
+        compat_login: config.compat_login_entrypoint.clone(),
         email: config.email_entrypoint.clone(),
     };
 

crates/config/src/sections/policy.rs

@@ -62,6 +62,14 @@ fn is_default_password_entrypoint(value: &String) -> bool {
     *value == default_password_entrypoint()
 }
 
+fn default_compat_login_entrypoint() -> String {
+    "compat_login/violation".to_owned()
+}
+
+fn is_default_compat_login_entrypoint(value: &String) -> bool {
+    *value == default_compat_login_entrypoint()
+}
+
 fn default_email_entrypoint() -> String {
     "email/violation".to_owned()
 }
@@ -111,6 +119,13 @@ pub struct PolicyConfig {
     )]
     pub authorization_grant_entrypoint: String,
 
+    /// Entrypoint to use when evaluating compatibility logins
+    #[serde(
+        default = "default_compat_login_entrypoint",
+        skip_serializing_if = "is_default_compat_login_entrypoint"
+    )]
+    pub compat_login_entrypoint: String,
+
     /// Entrypoint to use when changing password
     #[serde(
         default = "default_password_entrypoint",
@@ -137,6 +152,7 @@ impl Default for PolicyConfig {
             client_registration_entrypoint: default_client_registration_entrypoint(),
             register_entrypoint: default_register_entrypoint(),
             authorization_grant_entrypoint: default_authorization_grant_entrypoint(),
+            compat_login_entrypoint: default_compat_login_entrypoint(),
             password_entrypoint: default_password_entrypoint(),
             email_entrypoint: default_email_entrypoint(),
             data: default_data(),

crates/handlers/src/compat/login.rs

@@ -16,6 +16,7 @@ use mas_data_model::{
     User,
 };
 use mas_matrix::HomeserverConnection;
+use mas_policy::{Policy, Requester, ViolationCode, model::CompatLogin};
 use mas_storage::{
     BoxRepository, BoxRepositoryFactory, RepositoryAccess,
     compat::{
@@ -37,6 +38,7 @@ use crate::{
     BoundActivityTracker, Limiter, METER, RequesterFingerprint, impl_from_error_for_route,
     passwords::{PasswordManager, PasswordVerificationResult},
     rate_limit::PasswordCheckLimitedError,
+    session::count_user_sessions_for_limiting,
 };
 
 static LOGIN_COUNTER: LazyLock<Counter<u64>> = LazyLock::new(|| {
@@ -213,9 +215,16 @@ pub enum RouteError {
 
     #[error("failed to provision device")]
     ProvisionDeviceFailed(#[source] anyhow::Error),
+
+    #[error("login rejected by policy")]
+    PolicyRejected,
+
+    #[error("login rejected by policy (hard session limit reached)")]
+    PolicyHardSessionLimitReached,
 }
 
 impl_from_error_for_route!(mas_storage::RepositoryError);
+impl_from_error_for_route!(mas_policy::EvaluationError);
 
 impl From<anyhow::Error> for RouteError {
     fn from(err: anyhow::Error) -> Self {
@@ -274,6 +283,16 @@ impl IntoResponse for RouteError {
                 error: "User account has been locked",
                 status: StatusCode::UNAUTHORIZED,
             },
+            Self::PolicyRejected => MatrixError {
+                errcode: "M_FORBIDDEN",
+                error: "Login denied by the policy enforced by this service",
+                status: StatusCode::FORBIDDEN,
+            },
+            Self::PolicyHardSessionLimitReached => MatrixError {
+                errcode: "M_FORBIDDEN",
+                error: "You have reached your hard device limit. Please visit your account page to sign some out.",
+                status: StatusCode::FORBIDDEN,
+            },
         };
 
         (sentry_event_id, response).into_response()
@@ -290,6 +309,7 @@ pub(crate) async fn post(
     State(homeserver): State<Arc<dyn HomeserverConnection>>,
     State(site_config): State<SiteConfig>,
     State(limiter): State<Limiter>,
+    mut policy: Policy,
     requester: RequesterFingerprint,
     user_agent: Option<TypedHeader<headers::UserAgent>>,
     MatrixJsonBody(input): MatrixJsonBody<RequestBody>,
@@ -329,6 +349,11 @@ pub(crate) async fn post(
                 &limiter,
                 requester,
                 &mut repo,
+                &mut policy,
+                Requester {
+                    ip_address: activity_tracker.ip(),
+                    user_agent: user_agent.clone(),
+                },
                 username,
                 password,
                 input.device_id, // TODO check for validity
@@ -342,6 +367,11 @@ pub(crate) async fn post(
                 &mut rng,
                 &clock,
                 &mut repo,
+                &mut policy,
+                Requester {
+                    ip_address: activity_tracker.ip(),
+                    user_agent: user_agent.clone(),
+                },
                 &token,
                 input.device_id,
                 input.initial_device_display_name,
@@ -459,6 +489,8 @@ async fn token_login(
     rng: &mut (dyn RngCore + Send),
     clock: &dyn Clock,
     repo: &mut BoxRepository,
+    policy: &mut Policy,
+    requester: Requester,
     token: &str,
     requested_device_id: Option<String>,
     initial_device_display_name: Option<String>,
@@ -544,10 +576,38 @@ async fn token_login(
         Device::generate(rng)
     };
 
-    repo.app_session()
+    let session_replaced = repo
+        .app_session()
         .finish_sessions_to_replace_device(clock, &browser_session.user, &device)
         .await?;
 
+    let session_counts = count_user_sessions_for_limiting(repo, &browser_session.user).await?;
+
+    let res = policy
+        .evaluate_compat_login(mas_policy::CompatLoginInput {
+            user: &browser_session.user,
+            login: CompatLogin::Token,
+            session_replaced,
+            session_counts,
+            requester,
+        })
+        .await?;
+    if !res.valid() {
+        // If the only violation is that we have too many sessions, then handle that
+        // separately.
+        // In the future, we intend to evict some sessions automatically instead. We
+        // don't trigger this if there was some other violation anyway, since that means
+        // that removing a session wouldn't actually unblock the login.
+        if res.violations.len() == 1 {
+            let violation = &res.violations[0];
+            if violation.code == Some(ViolationCode::TooManySessions) {
+                // The only violation is having reached the session limit.
+                return Err(RouteError::PolicyHardSessionLimitReached);
+            }
+        }
+        return Err(RouteError::PolicyRejected);
+    }
+
     // We first create the session in the database, commit the transaction, then
     // create it on the homeserver, scheduling a device sync job afterwards to
     // make sure we don't end up in an inconsistent state.
@@ -578,6 +638,8 @@ async fn user_password_login(
     limiter: &Limiter,
     requester: RequesterFingerprint,
     repo: &mut BoxRepository,
+    policy: &mut Policy,
+    policy_requester: Requester,
     username: &str,
     password: String,
     requested_device_id: Option<String>,
@@ -647,10 +709,38 @@ async fn user_password_login(
         Device::generate(&mut rng)
     };
 
-    repo.app_session()
+    let session_replaced = repo
+        .app_session()
         .finish_sessions_to_replace_device(clock, &user, &device)
         .await?;
 
+    let session_counts = count_user_sessions_for_limiting(repo, &user).await?;
+
+    let res = policy
+        .evaluate_compat_login(mas_policy::CompatLoginInput {
+            user: &user,
+            login: CompatLogin::Password,
+            session_replaced,
+            session_counts,
+            requester: policy_requester,
+        })
+        .await?;
+    if !res.valid() {
+        // If the only violation is that we have too many sessions, then handle that
+        // separately.
+        // In the future, we intend to evict some sessions automatically instead. We
+        // don't trigger this if there was some other violation anyway, since that means
+        // that removing a session wouldn't actually unblock the login.
+        if res.violations.len() == 1 {
+            let violation = &res.violations[0];
+            if violation.code == Some(ViolationCode::TooManySessions) {
+                // The only violation is having reached the session limit.
+                return Err(RouteError::PolicyHardSessionLimitReached);
+            }
+        }
+        return Err(RouteError::PolicyRejected);
+    }
+
     let session = repo
         .compat_session()
         .add(

crates/handlers/src/compat/login_sso_complete.rs

@@ -11,23 +11,27 @@ use axum::{
     extract::{Form, Path, State},
     response::{Html, IntoResponse, Redirect, Response},
 };
-use axum_extra::extract::Query;
+use axum_extra::{TypedHeader, extract::Query};
 use chrono::Duration;
+use hyper::StatusCode;
 use mas_axum_utils::{
     InternalError,
     cookies::CookieJar,
     csrf::{CsrfExt, ProtectedForm},
 };
 use mas_data_model::{BoxClock, BoxRng, Clock};
+use mas_policy::{Policy, model::CompatLogin};
 use mas_router::{CompatLoginSsoAction, UrlBuilder};
 use mas_storage::{BoxRepository, RepositoryAccess, compat::CompatSsoLoginRepository};
-use mas_templates::{CompatSsoContext, ErrorContext, TemplateContext, Templates};
+use mas_templates::{
+    CompatLoginPolicyViolationContext, CompatSsoContext, ErrorContext, TemplateContext, Templates,
+};
 use serde::{Deserialize, Serialize};
 use ulid::Ulid;
 
 use crate::{
-    PreferredLanguage,
-    session::{SessionOrFallback, load_session_or_fallback},
+    BoundActivityTracker, PreferredLanguage,
+    session::{SessionOrFallback, count_user_sessions_for_limiting, load_session_or_fallback},
 };
 
 #[derive(Serialize)]
@@ -56,10 +60,15 @@ pub async fn get(
     mut repo: BoxRepository,
     State(templates): State<Templates>,
     State(url_builder): State<UrlBuilder>,
+    mut policy: Policy,
+    activity_tracker: BoundActivityTracker,
+    user_agent: Option<TypedHeader<headers::UserAgent>>,
     cookie_jar: CookieJar,
     Path(id): Path<Ulid>,
     Query(params): Query<Params>,
 ) -> Result<Response, InternalError> {
+    let user_agent = user_agent.map(|ua| ua.to_string());
+
     let (cookie_jar, maybe_session) = match load_session_or_fallback(
         cookie_jar, &clock, &mut rng, &templates, &locale, &mut repo,
     )
@@ -107,6 +116,35 @@ pub async fn get(
         return Ok((cookie_jar, Html(content)).into_response());
     }
 
+    let session_counts = count_user_sessions_for_limiting(&mut repo, &session.user).await?;
+
+    let res = policy
+        .evaluate_compat_login(mas_policy::CompatLoginInput {
+            user: &session.user,
+            login: CompatLogin::Sso {
+                redirect_uri: login.redirect_uri.to_string(),
+            },
+            // We don't know if there's going to be a replacement until we received the device ID,
+            // which happens too late.
+            session_replaced: false,
+            session_counts,
+            requester: mas_policy::Requester {
+                ip_address: activity_tracker.ip(),
+                user_agent,
+            },
+        })
+        .await?;
+    if !res.valid() {
+        let ctx = CompatLoginPolicyViolationContext::for_violations(res.violations)
+            .with_session(session)
+            .with_csrf(csrf_token.form_value())
+            .with_language(locale);
+
+        let content = templates.render_compat_login_policy_violation(&ctx)?;
+
+        return Ok((StatusCode::FORBIDDEN, cookie_jar, Html(content)).into_response());
+    }
+
     let ctx = CompatSsoContext::new(login)
         .with_session(session)
         .with_csrf(csrf_token.form_value())
@@ -129,11 +167,16 @@ pub async fn post(
     PreferredLanguage(locale): PreferredLanguage,
     State(templates): State<Templates>,
     State(url_builder): State<UrlBuilder>,
+    mut policy: Policy,
+    activity_tracker: BoundActivityTracker,
+    user_agent: Option<TypedHeader<headers::UserAgent>>,
     cookie_jar: CookieJar,
     Path(id): Path<Ulid>,
     Query(params): Query<Params>,
     Form(form): Form<ProtectedForm<()>>,
 ) -> Result<Response, InternalError> {
+    let user_agent = user_agent.map(|ua| ua.to_string());
+
     let (cookie_jar, maybe_session) = match load_session_or_fallback(
         cookie_jar, &clock, &mut rng, &templates, &locale, &mut repo,
     )
@@ -200,6 +243,37 @@ pub async fn post(
         redirect_uri
     };
 
+    let session_counts = count_user_sessions_for_limiting(&mut repo, &session.user).await?;
+
+    let res = policy
+        .evaluate_compat_login(mas_policy::CompatLoginInput {
+            user: &session.user,
+            login: CompatLogin::Sso {
+                redirect_uri: login.redirect_uri.to_string(),
+            },
+            session_counts,
+            // We don't know if there's going to be a replacement until we received the device ID,
+            // which happens too late.
+            session_replaced: false,
+            requester: mas_policy::Requester {
+                ip_address: activity_tracker.ip(),
+                user_agent,
+            },
+        })
+        .await?;
+
+    if !res.valid() {
+        let (csrf_token, cookie_jar) = cookie_jar.csrf_token(&clock, &mut rng);
+        let ctx = CompatLoginPolicyViolationContext::for_violations(res.violations)
+            .with_session(session)
+            .with_csrf(csrf_token.form_value())
+            .with_language(locale);
+
+        let content = templates.render_compat_login_policy_violation(&ctx)?;
+
+        return Ok((StatusCode::FORBIDDEN, cookie_jar, Html(content)).into_response());
+    }
+
     // Note that if the login is not Pending,
     // this fails and aborts the transaction.
     repo.compat_sso_login()

crates/handlers/src/lib.rs

@@ -272,6 +272,7 @@ where
     BoxRepository: FromRequestParts<S>,
     BoxClock: FromRequestParts<S>,
     BoxRng: FromRequestParts<S>,
+    Policy: FromRequestParts<S>,
 {
     // A sub-router for human-facing routes with error handling
     let human_router = Router::new()

crates/handlers/src/test_utils.rs

@@ -82,6 +82,7 @@ pub(crate) async fn policy_factory(
         register: "register/violation".to_owned(),
         client_registration: "client_registration/violation".to_owned(),
         authorization_grant: "authorization_grant/violation".to_owned(),
+        compat_login: "compat_login/violation".to_owned(),
         email: "email/violation".to_owned(),
     };