ksmbd: lock the binding preauth session in smb3_preauth_hash_rsp

smb3_preauth_hash_rsp() computes the SMB3.1.1 preauth integrity hash on
the response path. For a binding SESSION_SETUP it looks up the
per-connection preauth_session and reads its Preauth_HashValue.

smb2_sess_setup() frees that preauth_session under ksmbd_conn_lock().
Two SMB2 requests on one connection can run concurrently, so an unlocked
lookup and hash can use a preauth_session after another worker frees it.

Take ksmbd_conn_lock() before selecting conn->binding and hold it across
the selected preauth hash lookup and update. This preserves the existing
hash selection while preventing the lookup-to-use lifetime race.

Fixes: 1c5daa2 ("ksmbd: handle channel binding with a different user")
Signed-off-by: Gil Portnoy <dddhkts1@gmail.com>
Acked-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>

Author: dhkts1

fs/smb/server/smb2pdu.c

@@ -9808,22 +9808,21 @@ void smb3_preauth_hash_rsp(struct ksmbd_work *work)
 	}
 
 	if (le16_to_cpu(rsp->Command) == SMB2_SESSION_SETUP_HE && sess) {
-		__u8 *hash_value;
+		ksmbd_conn_lock(conn);
 
 		if (conn->binding) {
 			struct preauth_session *preauth_sess;
 
 			preauth_sess = ksmbd_preauth_session_lookup(conn, sess->id);
-			if (!preauth_sess)
-				return;
-			hash_value = preauth_sess->Preauth_HashValue;
-		} else {
-			hash_value = sess->Preauth_HashValue;
-			if (!hash_value)
-				return;
+			if (preauth_sess)
+				ksmbd_gen_preauth_integrity_hash(conn,
+					work->response_buf,
+					preauth_sess->Preauth_HashValue);
+		} else if (sess->Preauth_HashValue) {
+			ksmbd_gen_preauth_integrity_hash(conn, work->response_buf,
+					 sess->Preauth_HashValue);
 		}
-		ksmbd_gen_preauth_integrity_hash(conn, work->response_buf,
-						 hash_value);
+		ksmbd_conn_unlock(conn);
 	}
 }