From 4441cf762c6e7e62ca20c98b77799e1574095f41 Mon Sep 17 00:00:00 2001
From: Simon Kelley <simon@thekelleys.org.uk>
Date: Tue, 10 Apr 2018 21:39:54 +0100
Subject: [PATCH] Fix DNS server fd garbage collection.

If we're talking to upstream servers from a fixed port, specified by query-port
we create the fds to do this once, before dropping root, so that ports <1024 can be used.

But we call check_servers() before reading /etc/resolv.conf, so if the only servers
are in resolv.conf, at that point there will be no servers, and the fds get garbage
collected away, only to be recreated (but without root) after we read /etc/resolv.conf

Make pre-allocated server fds immortal, to avoid this problem.
---
 src/dnsmasq.h |  2 +-
 src/network.c | 13 +++++++++----
 2 files changed, 10 insertions(+), 5 deletions(-)

diff --git a/src/dnsmasq.h b/src/dnsmasq.h
index 30c4519..ff7172f 100644
--- a/src/dnsmasq.h
+++ b/src/dnsmasq.h
@@ -506,7 +506,7 @@ struct serverfd {
   int fd;
   union mysockaddr source_addr;
   char interface[IF_NAMESIZE+1];
-  unsigned int ifindex, used;
+  unsigned int ifindex, used, preallocated;
   struct serverfd *next;
 };
 
diff --git a/src/network.c b/src/network.c
index 1af4dbc..b405458 100644
--- a/src/network.c
+++ b/src/network.c
@@ -1290,6 +1290,7 @@ static struct serverfd *allocate_sfd(union mysockaddr *addr, char *intname)
   sfd->source_addr = *addr;
   sfd->next = daemon->sfds;
   sfd->ifindex = ifindex;
+  sfd->preallocated = 0;
   daemon->sfds = sfd;
 
   return sfd; 
@@ -1300,6 +1301,7 @@ static struct serverfd *allocate_sfd(union mysockaddr *addr, char *intname)
 void pre_allocate_sfds(void)
 {
   struct server *srv;
+  struct serverfd *sfd;
   
   if (daemon->query_port != 0)
     {
@@ -1311,7 +1313,8 @@ void pre_allocate_sfds(void)
 #ifdef HAVE_SOCKADDR_SA_LEN
       addr.in.sin_len = sizeof(struct sockaddr_in);
 #endif
-      allocate_sfd(&addr, "");
+      if ((sfd = allocate_sfd(&addr, "")))
+	sfd->preallocated = 1;
 #ifdef HAVE_IPV6
       memset(&addr, 0, sizeof(addr));
       addr.in6.sin6_family = AF_INET6;
@@ -1320,7 +1323,8 @@ void pre_allocate_sfds(void)
 #ifdef HAVE_SOCKADDR_SA_LEN
       addr.in6.sin6_len = sizeof(struct sockaddr_in6);
 #endif
-      allocate_sfd(&addr, "");
+      if ((sfd = allocate_sfd(&addr, "")))
+	sfd->preallocated = 1;
 #endif
     }
   
@@ -1473,9 +1477,10 @@ void check_servers(void)
   /* interface may be new since startup */
   if (!option_bool(OPT_NOWILD))
     enumerate_interfaces(0);
-  
+
+  /* don't garbage collect pre-allocated sfds. */
   for (sfd = daemon->sfds; sfd; sfd = sfd->next)
-    sfd->used = 0;
+    sfd->used = sfd->preallocated;
 
   for (count = 0, serv = daemon->servers; serv; serv = serv->next)
     {