ksmbd: fix racy issue from session lookup and expire

Increment the session reference count within the lock for lookup to avoid
racy issue with session expire.

Cc: [email protected]
Reported-by: [email protected] # ZDI-CAN-25737
Signed-off-by: Namjae Jeon <[email protected]>
Signed-off-by: Steve French <[email protected]>

Author: namjaejeon

fs/smb/server/auth.c

@@ -1016,6 +1016,8 @@ static int ksmbd_get_encryption_key(struct ksmbd_work *work, __u64 ses_id,
 
 	ses_enc_key = enc ? sess->smb3encryptionkey :
 		sess->smb3decryptionkey;
+	if (enc)
+		ksmbd_user_session_get(sess);
 	memcpy(key, ses_enc_key, SMB3_ENC_DEC_KEY_SIZE);
 
 	return 0;

fs/smb/server/mgmt/user_session.c

@@ -263,8 +263,10 @@ struct ksmbd_session *ksmbd_session_lookup(struct ksmbd_conn *conn,
 
 	down_read(&conn->session_lock);
 	sess = xa_load(&conn->sessions, id);
-	if (sess)
+	if (sess) {
 		sess->last_active = jiffies;
+		ksmbd_user_session_get(sess);
+	}
 	up_read(&conn->session_lock);
 	return sess;
 }
@@ -275,6 +277,8 @@ struct ksmbd_session *ksmbd_session_lookup_slowpath(unsigned long long id)
 
 	down_read(&sessions_table_lock);
 	sess = __session_lookup(id);
+	if (sess)
+		ksmbd_user_session_get(sess);
 	up_read(&sessions_table_lock);
 
 	return sess;

fs/smb/server/server.c

@@ -241,14 +241,14 @@ static void __handle_ksmbd_work(struct ksmbd_work *work,
 	if (work->tcon)
 		ksmbd_tree_connect_put(work->tcon);
 	smb3_preauth_hash_rsp(work);
-	if (work->sess)
-		ksmbd_user_session_put(work->sess);
 	if (work->sess && work->sess->enc && work->encrypted &&
 	    conn->ops->encrypt_resp) {
 		rc = conn->ops->encrypt_resp(work);
 		if (rc < 0)
 			conn->ops->set_rsp_status(work, STATUS_DATA_ERROR);
 	}
+	if (work->sess)
+		ksmbd_user_session_put(work->sess);
 
 	ksmbd_conn_write(work);
 }

fs/smb/server/smb2pdu.c

@@ -67,8 +67,10 @@ static inline bool check_session_id(struct ksmbd_conn *conn, u64 id)
 		return false;
 
 	sess = ksmbd_session_lookup_all(conn, id);
-	if (sess)
+	if (sess) {
+		ksmbd_user_session_put(sess);
 		return true;
+	}
 	pr_err("Invalid user session id: %llu\n", id);
 	return false;
 }
@@ -605,10 +607,8 @@ int smb2_check_user_session(struct ksmbd_work *work)
 
 	/* Check for validity of user session */
 	work->sess = ksmbd_session_lookup_all(conn, sess_id);
-	if (work->sess) {
-		ksmbd_user_session_get(work->sess);
+	if (work->sess)
 		return 1;
-	}
 	ksmbd_debug(SMB, "Invalid user session, Uid %llu\n", sess_id);
 	return -ENOENT;
 }
@@ -1701,37 +1701,44 @@ int smb2_sess_setup(struct ksmbd_work *work)
 
 		if (conn->dialect != sess->dialect) {
 			rc = -EINVAL;
+			ksmbd_user_session_put(sess);
 			goto out_err;
 		}
 
 		if (!(req->hdr.Flags & SMB2_FLAGS_SIGNED)) {
 			rc = -EINVAL;
+			ksmbd_user_session_put(sess);
 			goto out_err;
 		}
 
 		if (strncmp(conn->ClientGUID, sess->ClientGUID,
 			    SMB2_CLIENT_GUID_SIZE)) {
 			rc = -ENOENT;
+			ksmbd_user_session_put(sess);
 			goto out_err;
 		}
 
 		if (sess->state == SMB2_SESSION_IN_PROGRESS) {
 			rc = -EACCES;
+			ksmbd_user_session_put(sess);
 			goto out_err;
 		}
 
 		if (sess->state == SMB2_SESSION_EXPIRED) {
 			rc = -EFAULT;
+			ksmbd_user_session_put(sess);
 			goto out_err;
 		}
+		ksmbd_user_session_put(sess);
 
 		if (ksmbd_conn_need_reconnect(conn)) {
 			rc = -EFAULT;
 			sess = NULL;
 			goto out_err;
 		}
 
-		if (ksmbd_session_lookup(conn, sess_id)) {
+		sess = ksmbd_session_lookup(conn, sess_id);
+		if (!sess) {
 			rc = -EACCES;
 			goto out_err;
 		}
@@ -1742,7 +1749,6 @@ int smb2_sess_setup(struct ksmbd_work *work)
 		}
 
 		conn->binding = true;
-		ksmbd_user_session_get(sess);
 	} else if ((conn->dialect < SMB30_PROT_ID ||
 		    server_conf.flags & KSMBD_GLOBAL_FLAG_SMB3_MULTICHANNEL) &&
 		   (req->Flags & SMB2_SESSION_REQ_FLAG_BINDING)) {
@@ -1769,7 +1775,6 @@ int smb2_sess_setup(struct ksmbd_work *work)
 		}
 
 		conn->binding = false;
-		ksmbd_user_session_get(sess);
 	}
 	work->sess = sess;
 
@@ -2197,9 +2202,9 @@ int smb2_tree_disconnect(struct ksmbd_work *work)
 int smb2_session_logoff(struct ksmbd_work *work)
 {
 	struct ksmbd_conn *conn = work->conn;
+	struct ksmbd_session *sess = work->sess;
 	struct smb2_logoff_req *req;
 	struct smb2_logoff_rsp *rsp;
-	struct ksmbd_session *sess;
 	u64 sess_id;
 	int err;
 
@@ -2221,11 +2226,6 @@ int smb2_session_logoff(struct ksmbd_work *work)
 	ksmbd_close_session_fds(work);
 	ksmbd_conn_wait_idle(conn);
 
-	/*
-	 * Re-lookup session to validate if session is deleted
-	 * while waiting request complete
-	 */
-	sess = ksmbd_session_lookup_all(conn, sess_id);
 	if (ksmbd_tree_conn_session_logoff(sess)) {
 		ksmbd_debug(SMB, "Invalid tid %d\n", req->hdr.Id.SyncId.TreeId);
 		rsp->hdr.Status = STATUS_NETWORK_NAME_DELETED;
@@ -8992,6 +8992,7 @@ int smb3_decrypt_req(struct ksmbd_work *work)
 		       le64_to_cpu(tr_hdr->SessionId));
 		return -ECONNABORTED;
 	}
+	ksmbd_user_session_put(sess);
 
 	iov[0].iov_base = buf;
 	iov[0].iov_len = sizeof(struct smb2_transform_hdr) + 4;