Validate the messageLength field of incoming messages.

The PTP messageLength field is redundant because the length of a PTP
message is precisely determined by the message type and the appended
TLVs.  The current implementation validates the sizes of both the main
message (according to the fixed header length and fixed length by
type) and the TLVs (by using the 'L' of the TLV).

However, when forwarding a message, the messageLength field is used.
If a message arrives with a messageLength field larger than the actual
message size, the code will read and possibly write data beyond the
allocated buffer.

Fix the issue by validating the field on ingress.  This prevents
reading and sending data past the message buffer when forwarding a
management message or other messages when operating as a transparent
clock, and it also prevents a memory corruption in msg_post_recv()
after forwarding a management message.

Reported-by: Miroslav Lichvar <mlichvar@redhat.com>
Signed-off-by: Richard Cochran <richardcochran@gmail.com>

msg.c

@@ -184,7 +184,7 @@ static int suffix_post_recv(struct ptp_message *msg, int len)
 {
 	uint8_t *ptr = msg_suffix(msg);
 	struct tlv_extra *extra;
-	int err;
+	int err, suffix_len = 0;
 
 	if (!ptr)
 		return 0;
@@ -202,12 +202,14 @@ static int suffix_post_recv(struct ptp_message *msg, int len)
 			tlv_extra_recycle(extra);
 			return -EBADMSG;
 		}
+		suffix_len += sizeof(struct TLV);
 		len -= sizeof(struct TLV);
 		ptr += sizeof(struct TLV);
 		if (extra->tlv->length > len) {
 			tlv_extra_recycle(extra);
 			return -EBADMSG;
 		}
+		suffix_len += extra->tlv->length;
 		len -= extra->tlv->length;
 		ptr += extra->tlv->length;
 		err = tlv_post_recv(extra);
@@ -217,7 +219,7 @@ static int suffix_post_recv(struct ptp_message *msg, int len)
 		}
 		msg_tlv_attach(msg, extra);
 	}
-	return 0;
+	return suffix_len;
 }
 
 static void suffix_pre_send(struct ptp_message *msg)
@@ -335,7 +337,7 @@ void msg_get(struct ptp_message *m)
 
 int msg_post_recv(struct ptp_message *m, int cnt)
 {
-	int pdulen, type, err;
+	int err, pdulen, suffix_len, type;
 
 	if (cnt < sizeof(struct ptp_header))
 		return -EBADMSG;
@@ -420,9 +422,13 @@ int msg_post_recv(struct ptp_message *m, int cnt)
 		break;
 	}
 
-	err = suffix_post_recv(m, cnt - pdulen);
-	if (err)
-		return err;
+	suffix_len = suffix_post_recv(m, cnt - pdulen);
+	if (suffix_len < 0) {
+		return suffix_len;
+	}
+	if (pdulen + suffix_len != m->header.messageLength) {
+		return -EBADMSG;
+	}
 
 	return 0;
 }