musl: add upstream security fix for CVE-2017-15650

>From the upstream announcement:
http://www.openwall.com/lists/oss-security/2017/10/19/5

Felix Wilhelm has discovered a flaw in the dns response parsing for
musl libc 1.1.16 that leads to overflow of a stack-based buffer.
Earlier versions are also affected.

When an application makes a request via getaddrinfo for both IPv4 and
IPv6 results (AF_UNSPEC), an attacker who controls or can spoof the
nameservers configured in resolv.conf can reply to both the A and AAAA
queries with A results. Since A records are smaller than AAAA records,
it's possible to fit more addresses than the precomputed bound, and a
buffer overflow occurs.

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
(cherry picked from commit 209f42fd3a5f4357e22fb72f1597a6868566aabd)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/musl/0003-in-dns-parsing-callback-enforce-MAXADDRS-to-preclude.patch

@@ -0,0 +1,35 @@
+From 45ca5d3fcb6f874bf5ba55d0e9651cef68515395 Mon Sep 17 00:00:00 2001
+From: Rich Felker <dalias@aerifal.cx>
+Date: Wed, 18 Oct 2017 14:50:03 -0400
+Subject: [PATCH] in dns parsing callback, enforce MAXADDRS to preclude
+ overflow
+
+MAXADDRS was chosen not to need enforcement, but the logic used to
+compute it assumes the answers received match the RR types of the
+queries. specifically, it assumes that only one replu contains A
+record answers. if the replies to both the A and the AAAA query have
+their answer sections filled with A records, MAXADDRS can be exceeded
+and clobber the stack of the calling function.
+
+this bug was found and reported by Felix Wilhelm.
+
+Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
+---
+ src/network/lookup_name.c | 1 +
+ 1 file changed, 1 insertion(+)
+
+diff --git a/src/network/lookup_name.c b/src/network/lookup_name.c
+index 066be4d5..209c20f0 100644
+--- a/src/network/lookup_name.c
++++ b/src/network/lookup_name.c
+@@ -111,6 +111,7 @@ static int dns_parse_callback(void *c, int rr, const void *data, int len, const
+ {
+ 	char tmp[256];
+ 	struct dpc_ctx *ctx = c;
++	if (ctx->cnt >= MAXADDRS) return -1;
+ 	switch (rr) {
+ 	case RR_A:
+ 		if (len != 4) return -1;
+-- 
+2.11.0
+