ksmbd: limit pdu length size according to connection status

Stream protocol length will never be larger than 16KB until session setup.
After session setup, the size of requests will not be larger than
16KB + SMB2 MAX WRITE size. This patch limits these invalidly oversized
requests and closes the connection immediately.

Fixes: 0626e66 ("cifsd: add server handler for central processing and tranport layers")
Cc: [email protected]
Reported-by: [email protected] # ZDI-CAN-18259
Signed-off-by: Namjae Jeon <[email protected]>
Signed-off-by: Steve French <[email protected]>

Author: namjaejeon

fs/ksmbd/connection.c

@@ -280,7 +280,7 @@ int ksmbd_conn_handler_loop(void *p)
 {
 	struct ksmbd_conn *conn = (struct ksmbd_conn *)p;
 	struct ksmbd_transport *t = conn->transport;
-	unsigned int pdu_size;
+	unsigned int pdu_size, max_allowed_pdu_size;
 	char hdr_buf[4] = {0,};
 	int size;
 
@@ -305,13 +305,26 @@ int ksmbd_conn_handler_loop(void *p)
 		pdu_size = get_rfc1002_len(hdr_buf);
 		ksmbd_debug(CONN, "RFC1002 header %u bytes\n", pdu_size);
 
+		if (conn->status == KSMBD_SESS_GOOD)
+			max_allowed_pdu_size =
+				SMB3_MAX_MSGSIZE + conn->vals->max_write_size;
+		else
+			max_allowed_pdu_size = SMB3_MAX_MSGSIZE;
+
+		if (pdu_size > max_allowed_pdu_size) {
+			pr_err_ratelimited("PDU length(%u) excceed maximum allowed pdu size(%u) on connection(%d)\n",
+					pdu_size, max_allowed_pdu_size,
+					conn->status);
+			break;
+		}
+
 		/*
 		 * Check if pdu size is valid (min : smb header size,
 		 * max : 0x00FFFFFF).
 		 */
 		if (pdu_size < __SMB2_HEADER_STRUCTURE_SIZE ||
 		    pdu_size > MAX_STREAM_PROT_LEN) {
-			continue;
+			break;
 		}
 
 		/* 4 for rfc1002 length field */

fs/ksmbd/smb2pdu.h

@@ -24,8 +24,9 @@
 
 #define SMB21_DEFAULT_IOSIZE	(1024 * 1024)
 #define SMB3_DEFAULT_TRANS_SIZE	(1024 * 1024)
-#define SMB3_MIN_IOSIZE	(64 * 1024)
-#define SMB3_MAX_IOSIZE	(8 * 1024 * 1024)
+#define SMB3_MIN_IOSIZE		(64 * 1024)
+#define SMB3_MAX_IOSIZE		(8 * 1024 * 1024)
+#define SMB3_MAX_MSGSIZE	(4 * 4096)
 
 /*
  *	Definitions for SMB2 Protocol Data Units (network frames)