From 64de7dc7fd06470424bb4c3ea537f542c46895c4 Mon Sep 17 00:00:00 2001
From: Michael Brown <mcb30@ipxe.org>
Date: Tue, 21 Mar 2017 14:57:36 +0200
Subject: [PATCH] [slam] Avoid NULL pointer dereference in slam_pull_value()

Signed-off-by: Michael Brown <mcb30@ipxe.org>
---
 src/net/udp/slam.c | 14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/src/net/udp/slam.c b/src/net/udp/slam.c
index 61dd7d98..c165b4fb 100644
--- a/src/net/udp/slam.c
+++ b/src/net/udp/slam.c
@@ -400,12 +400,16 @@ static int slam_pull_value ( struct slam_request *slam,
 		return -EINVAL;
 	}
 
-	/* Read value */
+	/* Strip value */
 	iob_pull ( iobuf, len );
-	*value = ( *data & 0x1f );
-	while ( --len ) {
-		*value <<= 8;
-		*value |= *(++data);
+
+	/* Read value, if applicable */
+	if ( value ) {
+		*value = ( *data & 0x1f );
+		while ( --len ) {
+			*value <<= 8;
+			*value |= *(++data);
+		}
 	}
 
 	return 0;