Avoid an out-of-bounds read in the redis-sentinel

The Redis sentinel would crash with a segfault after a few minutes because
it tried to read from a page without read permissions. Check up front
whether the sds is long enough to contain redis:slave or redis:master
before memcmp() as is done everywhere else in sentinelRefreshInstanceInfo().

From Nam Nguyen

databases/redis/Makefile

@@ -1,9 +1,10 @@
-# $OpenBSD: Makefile,v 1.113 2020/06/14 07:35:36 tb Exp $
+# $OpenBSD: Makefile,v 1.114 2020/06/28 10:47:15 tb Exp $
 
 COMMENT =		persistent key-value database
 DISTNAME =		redis-6.0.5
 CATEGORIES =		databases
 HOMEPAGE =		https://redis.io/
+REVISION =		0
 
 # BSD
 PERMIT_PACKAGE =	Yes

databases/redis/patches/patch-src_sentinel_c

@@ -0,0 +1,18 @@
+$OpenBSD: patch-src_sentinel_c,v 1.1 2020/06/28 10:47:15 tb Exp $
+
+redis-sentinel out of bounds memory access from memcmp
+
+Index: src/sentinel.c
+--- src/sentinel.c.orig
++++ src/sentinel.c
+@@ -2217,8 +2217,8 @@ void sentinelRefreshInstanceInfo(sentinelRedisInstance
+         }
+ 
+         /* role:<role> */
+-        if (!memcmp(l,"role:master",11)) role = SRI_MASTER;
+-        else if (!memcmp(l,"role:slave",10)) role = SRI_SLAVE;
++        if (sdslen(l) >= 11 && !memcmp(l,"role:master",11)) role = SRI_MASTER;
++        else if (sdslen(l) >= 10 && !memcmp(l,"role:slave",10)) role = SRI_SLAVE;
+ 
+         if (role == SRI_SLAVE) {
+             /* master_host:<host> */