commit 6b61ba29c78e26109426429c6d6b354f6e4443cd
Author: David Mirabito via Linuxptp-devel <linuxptp-devel@lists.sourceforge.net>
Date:   Tue Mar 19 13:42:48 2019 +1100

    Avoid fault when receiving zero length packets
    
    The manpage for recvmsg says -1 will be returned on error, Zero indicates an
    "orderly shutdown", presumably only in case of stream sockets.
    Further, UNIX Network Programming, Vol 1 says ".. a return value of 0 from
    recvfrom is acceptable for a datagram protocol"
    
    Such packets have been observed in the wild, aimed at PTP's multicast
    address and port, possibly related to malformed management queries.
    
    Patch to properly check return from recvmesg and not trigger the fault
    codepath. Instead, such packets are treated as "Bad Message" the same as
    non-zero but still too-short UDP payloads.
    
    Signed-off-by: David Mirabito <davidjm@arista.com>

diff --git a/port.c b/port.c
index ad9554f..9264211 100644
--- a/port.c
+++ b/port.c
@@ -2563,7 +2563,7 @@ static enum fsm_event bc_event(struct port *p, int fd_index)
 	msg->hwts.type = p->timestamping;
 
 	cnt = transport_recv(p->trp, fd, msg);
-	if (cnt <= 0) {
+	if (cnt < 0) {
 		pr_err("port %hu: recv message failed", portnum(p));
 		msg_put(msg);
 		return EV_FAULT_DETECTED;
diff --git a/sk.c b/sk.c
index 30162eb..93ba77a 100644
--- a/sk.c
+++ b/sk.c
@@ -359,7 +359,7 @@ int sk_receive(int fd, void *buf, int buflen,
 	}
 
 	cnt = recvmsg(fd, &msg, flags);
-	if (cnt < 1)
+	if (cnt < 0)
 		pr_err("recvmsg%sfailed: %m",
 		       flags == MSG_ERRQUEUE ? " tx timestamp " : " ");