Fix for CVE-2014-0195

A buffer overrun attack can be triggered by sending invalid DTLS fragments
to an OpenSSL DTLS client or server. This is potentially exploitable to
run arbitrary code on a vulnerable client or server.

Fixed by adding consistency check for DTLS fragments.

Thanks to Jüri Aedla for reporting this issue.

Author: snhenson

ssl/d1_both.c

@@ -627,7 +627,16 @@ dtls1_reassemble_fragment(SSL *s, struct hm_header_st* msg_hdr, int *ok)
 		frag->msg_header.frag_off = 0;
 		}
 	else
+		{
 		frag = (hm_fragment*) item->data;
+		if (frag->msg_header.msg_len != msg_hdr->msg_len)
+			{
+			item = NULL;
+			frag = NULL;
+			goto err;
+			}
+		}
+
 
 	/* If message is already reassembled, this must be a
 	 * retransmit and can be dropped.