[openib-general] [PATCH] libibumad: nit on short mad read

[Eitan Zahavi]

Hi Hal

This was reported to me by Ishai R. 

Consider function umad_recv line 810:
	if ((n = read(port->dev_fd, umad, sizeof *mad + *length)) <= 
	     sizeof *mad + *length) {
		DEBUG("mad received by agent %d length %d", mad->agent_id, n);
		*length = n - sizeof *mad;
		return mad->agent_id;
	}

	if (n == -EWOULDBLOCK) {
		if (!errno)
			errno = EWOULDBLOCK;
		return n;
	}

Seems that umad.c umad_recv would never go through the second "if" 
as if the read return n < 0 it will be cought by the first "if".

Then I have noticed that a wrap around of the returned length is also 
possible.

The patch fixes these issue.

Eitan

Signed-off-by:  Eitan Zahavi <eitan at mellanox.co.il>

Index: libibumad/src/umad.c
===================================================================
--- libibumad/src/umad.c	(revision 8313)
+++ libibumad/src/umad.c	(working copy)
@@ -806,10 +806,13 @@ umad_recv(int portid, void *umad, int *l
 		return n;
 	}
 
-	if ((n = read(port->dev_fd, umad, sizeof *mad + *length)) <= 
-	     sizeof *mad + *length) {
+	n = read(port->dev_fd, umad, sizeof *mad + *length);
+	if ((n >= 0) && (n <= sizeof *mad + *length)) {
 		DEBUG("mad received by agent %d length %d", mad->agent_id, n);
+		if (n > sizeof *mad)
 			*length = n - sizeof *mad;
+		else
+			*length = 0;
 		return mad->agent_id;
 	}