From 0506a5ed4e56863627c54aedad30ad61221292ef Mon Sep 17 00:00:00 2001
From: Simon Kelley <simon@thekelleys.org.uk>
Date: Thu, 19 Mar 2020 21:56:45 +0000
Subject: [PATCH] Handle old kernels that don't do NETLINK_NO_ENOBUFS.

Deal with both old kernel header files that don't define it,
and old kernels that don't implement it.

Also generalise Linux kernel version handling.
---
 src/dnsmasq.c |  6 +++++-
 src/dnsmasq.h |  6 +++++-
 src/ipset.c   | 17 +----------------
 src/netlink.c |  8 ++++++--
 src/util.c    | 23 +++++++++++++++++++++++
 5 files changed, 40 insertions(+), 20 deletions(-)

diff --git a/src/dnsmasq.c b/src/dnsmasq.c
index 286a1cd..74938ff 100644
--- a/src/dnsmasq.c
+++ b/src/dnsmasq.c
@@ -89,11 +89,15 @@ int main (int argc, char **argv)
   sigaction(SIGPIPE, &sigact, NULL);
 
   umask(022); /* known umask, create leases and pid files as 0644 */
- 
+
   rand_init(); /* Must precede read_opts() */
   
   read_opts(argc, argv, compile_opts);
  
+#ifdef HAVE_LINUX_NETWORK
+  daemon->kernel_version = kernel_version();
+#endif
+
   if (daemon->edns_pktsz < PACKETSZ)
     daemon->edns_pktsz = PACKETSZ;
 
diff --git a/src/dnsmasq.h b/src/dnsmasq.h
index 7349332..f747868 100644
--- a/src/dnsmasq.h
+++ b/src/dnsmasq.h
@@ -141,6 +141,7 @@ typedef unsigned long long u64;
 #endif
 
 #if defined(HAVE_LINUX_NETWORK)
+#include <linux/version.h>
 #include <linux/sockios.h>
 #include <linux/capability.h>
 /* There doesn't seem to be a universally-available 
@@ -1108,7 +1109,7 @@ extern struct daemon {
   int inotifyfd;
 #endif
 #if defined(HAVE_LINUX_NETWORK)
-  int netlinkfd;
+  int netlinkfd, kernel_version;
 #elif defined(HAVE_BSD_NETWORK)
   int dhcp_raw_fd, dhcp_icmp_fd, routefd;
 #endif
@@ -1288,6 +1289,9 @@ int read_write(int fd, unsigned char *packet, int size, int rw);
 void close_fds(long max_fd, int spare1, int spare2, int spare3);
 int wildcard_match(const char* wildcard, const char* match);
 int wildcard_matchn(const char* wildcard, const char* match, int num);
+#ifdef HAVE_LINUX_NETWORK
+int kernel_version(void);
+#endif
 
 /* log.c */
 void die(char *message, char *arg1, int exit_code) ATTRIBUTE_NORETURN;
diff --git a/src/ipset.c b/src/ipset.c
index 7b97ea8..0c014cb 100644
--- a/src/ipset.c
+++ b/src/ipset.c
@@ -22,9 +22,7 @@
 #include <errno.h>
 #include <sys/types.h>
 #include <sys/socket.h>
-#include <sys/utsname.h>
 #include <arpa/inet.h>
-#include <linux/version.h>
 #include <linux/netlink.h>
 
 /* We want to be able to compile against old header files
@@ -87,20 +85,7 @@ static inline void add_attr(struct nlmsghdr *nlh, uint16_t type, size_t len, con
 
 void ipset_init(void)
 {
-  struct utsname utsname;
-  int version;
-  char *split;
-  
-  if (uname(&utsname) < 0)
-    die(_("failed to find kernel version: %s"), NULL, EC_MISC);
-  
-  split = strtok(utsname.release, ".");
-  version = (split ? atoi(split) : 0);
-  split = strtok(NULL, ".");
-  version = version * 256 + (split ? atoi(split) : 0);
-  split = strtok(NULL, ".");
-  version = version * 256 + (split ? atoi(split) : 0);
-  old_kernel = (version < KERNEL_VERSION(2,6,32));
+  old_kernel = (daemon->kernel_version < KERNEL_VERSION(2,6,32));
   
   if (old_kernel && (ipset_sock = socket(AF_INET, SOCK_RAW, IPPROTO_RAW)) != -1)
     return;
diff --git a/src/netlink.c b/src/netlink.c
index a1ca5d1..3af54c4 100644
--- a/src/netlink.c
+++ b/src/netlink.c
@@ -27,6 +27,9 @@
 #define SOL_NETLINK 270
 #endif
 
+#ifndef NETLINK_NO_ENOBUFS
+#define NETLINK_NO_ENOBUFS 5
+#endif
 
 /* linux 2.6.19 buggers up the headers, patch it up here. */ 
 #ifndef IFA_RTA
@@ -79,10 +82,11 @@ void netlink_init(void)
     }
   
   if (daemon->netlinkfd == -1 || 
-      setsockopt(daemon->netlinkfd, SOL_NETLINK, NETLINK_NO_ENOBUFS, &opt, sizeof(opt)) == -1 ||
+      (daemon->kernel_version >= KERNEL_VERSION(2,6,30) &&
+       setsockopt(daemon->netlinkfd, SOL_NETLINK, NETLINK_NO_ENOBUFS, &opt, sizeof(opt)) == -1) ||
       getsockname(daemon->netlinkfd, (struct sockaddr *)&addr, &slen) == -1)
     die(_("cannot create netlink socket: %s"), NULL, EC_MISC);
-   
+  
   /* save pid assigned by bind() and retrieved by getsockname() */ 
   netlink_pid = addr.nl_pid;
   
diff --git a/src/util.c b/src/util.c
index 0b0c7de..5f13027 100644
--- a/src/util.c
+++ b/src/util.c
@@ -30,6 +30,10 @@
 #include <idna.h>
 #endif
 
+#ifdef HAVE_LINUX_NETWORK
+#include <sys/utsname.h>
+#endif
+
 /* SURF random number generator */
 
 static u32 seed[32];
@@ -782,3 +786,22 @@ int wildcard_matchn(const char* wildcard, const char* match, int num)
 
   return (!num) || (*wildcard == *match);
 }
+
+#ifdef HAVE_LINUX_NETWORK
+int kernel_version(void)
+{
+  struct utsname utsname;
+  int version;
+  char *split;
+  
+  if (uname(&utsname) < 0)
+    die(_("failed to find kernel version: %s"), NULL, EC_MISC);
+  
+  split = strtok(utsname.release, ".");
+  version = (split ? atoi(split) : 0);
+  split = strtok(NULL, ".");
+  version = version * 256 + (split ? atoi(split) : 0);
+  split = strtok(NULL, ".");
+  return version * 256 + (split ? atoi(split) : 0);
+}
+#endif