ksmbd: destroy expired sessions

client can indefinitely send smb2 session setup requests with
the SessionId set to 0, thus indefinitely spawning new sessions,
and causing indefinite memory usage. This patch limit to the number
of sessions using expired timeout and session state.

Cc: stable@vger.kernel.org
Reported-by: zdi-disclosures@trendmicro.com # ZDI-CAN-20478
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>

Author: namjaejeon

fs/ksmbd/mgmt/user_session.c

@@ -165,70 +165,73 @@ static struct ksmbd_session *__session_lookup(unsigned long long id)
 	struct ksmbd_session *sess;
 
 	hash_for_each_possible(sessions_table, sess, hlist, id) {
-		if (id == sess->id)
+		if (id == sess->id) {
+			sess->last_active = jiffies;
 			return sess;
+		}
 	}
 	return NULL;
 }
 
+static void ksmbd_expire_session(struct ksmbd_conn *conn)
+{
+	unsigned long id;
+	struct ksmbd_session *sess;
+
+	xa_for_each(&conn->sessions, id, sess) {
+		if (sess->state != SMB2_SESSION_VALID ||
+		    time_after(jiffies,
+			       sess->last_active + SMB2_SESSION_TIMEOUT)) {
+			xa_erase(&conn->sessions, sess->id);
+			ksmbd_session_destroy(sess);
+			continue;
+		}
+	}
+}
+
 int ksmbd_session_register(struct ksmbd_conn *conn,
 			   struct ksmbd_session *sess)
 {
 	sess->dialect = conn->dialect;
 	memcpy(sess->ClientGUID, conn->ClientGUID, SMB2_CLIENT_GUID_SIZE);
+	ksmbd_expire_session(conn);
 	return xa_err(xa_store(&conn->sessions, sess->id, sess, GFP_KERNEL));
 }
 
-static int ksmbd_chann_del(struct ksmbd_conn *conn, struct ksmbd_session *sess)
+static void ksmbd_chann_del(struct ksmbd_conn *conn, struct ksmbd_session *sess)
 {
 	struct channel *chann;
 
 	chann = xa_erase(&sess->ksmbd_chann_list, (long)conn);
 	if (!chann)
-		return -ENOENT;
+		return;
 
 	kfree(chann);
-
-	return 0;
 }
 
 void ksmbd_sessions_deregister(struct ksmbd_conn *conn)
 {
 	struct ksmbd_session *sess;
+	unsigned long id;
 
-	if (conn->binding) {
-		int bkt;
-
-		down_write(&sessions_table_lock);
-		hash_for_each(sessions_table, bkt, sess, hlist) {
-			if (!ksmbd_chann_del(conn, sess)) {
-				up_write(&sessions_table_lock);
-				goto sess_destroy;
-			}
+	xa_for_each(&conn->sessions, id, sess) {
+		ksmbd_chann_del(conn, sess);
+		if (xa_empty(&sess->ksmbd_chann_list)) {
+			xa_erase(&conn->sessions, sess->id);
+			ksmbd_session_destroy(sess);
 		}
-		up_write(&sessions_table_lock);
-	} else {
-		unsigned long id;
-
-		xa_for_each(&conn->sessions, id, sess) {
-			if (!ksmbd_chann_del(conn, sess))
-				goto sess_destroy;
-		}
-	}
-
-	return;
-
-sess_destroy:
-	if (xa_empty(&sess->ksmbd_chann_list)) {
-		xa_erase(&conn->sessions, sess->id);
-		ksmbd_session_destroy(sess);
 	}
 }
 
 struct ksmbd_session *ksmbd_session_lookup(struct ksmbd_conn *conn,
 					   unsigned long long id)
 {
-	return xa_load(&conn->sessions, id);
+	struct ksmbd_session *sess;
+
+	sess = xa_load(&conn->sessions, id);
+	if (sess)
+		sess->last_active = jiffies;
+	return sess;
 }
 
 struct ksmbd_session *ksmbd_session_lookup_slowpath(unsigned long long id)
@@ -237,6 +240,8 @@ struct ksmbd_session *ksmbd_session_lookup_slowpath(unsigned long long id)
 
 	down_read(&sessions_table_lock);
 	sess = __session_lookup(id);
+	if (sess)
+		sess->last_active = jiffies;
 	up_read(&sessions_table_lock);
 
 	return sess;
@@ -315,6 +320,7 @@ static struct ksmbd_session *__session_create(int protocol)
 	if (ksmbd_init_file_table(&sess->file_table))
 		goto error;
 
+	sess->last_active = jiffies;
 	sess->state = SMB2_SESSION_IN_PROGRESS;
 	set_session_flag(sess, protocol);
 	xa_init(&sess->tree_conns);

fs/ksmbd/mgmt/user_session.h

@@ -59,6 +59,7 @@ struct ksmbd_session {
 	__u8				smb3signingkey[SMB3_SIGN_KEY_SIZE];
 
 	struct ksmbd_file_table		file_table;
+	unsigned long			last_active;
 };
 
 static inline int test_session_flag(struct ksmbd_session *sess, int bit)

fs/ksmbd/smb2pdu.c

@@ -1838,6 +1838,7 @@ int smb2_sess_setup(struct ksmbd_work *work)
 			if (sess->user && sess->user->flags & KSMBD_USER_FLAG_DELAY_SESSION)
 				try_delay = true;
 
+			sess->last_active = jiffies;
 			sess->state = SMB2_SESSION_EXPIRED;
 			if (try_delay)
 				ssleep(5);

fs/ksmbd/smb2pdu.h

@@ -61,6 +61,8 @@ struct preauth_integrity_info {
 #define SMB2_SESSION_IN_PROGRESS	BIT(0)
 #define SMB2_SESSION_VALID		BIT(1)
 
+#define SMB2_SESSION_TIMEOUT		(10 * HZ)
+
 struct create_durable_req_v2 {
 	struct create_context ccontext;
 	__u8   Name[8];