From: Eric Dumazet <edumazet@google.com>
Date: Wed, 4 Apr 2018 08:35:10 -0700
Subject: inet: frags: fix ip6frag_low_thresh boundary
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
Patch-mainline: v4.17-rc1
Git-commit: 3d23401283e80ceb03f765842787e0e79ff598b7
References: CVE-2018-5391 bsc#1103097

Giving an integer to proc_doulongvec_minmax() is dangerous on 64bit arches,
since linker might place next to it a non zero value preventing a change
to ip6frag_low_thresh.

ip6frag_low_thresh is not used anymore in the kernel, but we do not
want to prematuraly break user scripts wanting to change it.

Since specifying a minimal value of 0 for proc_doulongvec_minmax()
is moot, let's remove these zero values in all defrag units.

Fixes: 6e00f7dd5e4e ("ipv6: frags: fix /proc/sys/net/ipv6/ip6frag_low_thresh")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Maciej Żenczykowski <maze@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Acked-by: Michal Kubecek <mkubecek@suse.cz>

---
 net/ieee802154/6lowpan/reassembly.c     | 2 --
 net/ipv4/ip_fragment.c                  | 5 ++---
 net/ipv6/netfilter/nf_conntrack_reasm.c | 2 --
 net/ipv6/reassembly.c                   | 2 --
 4 files changed, 2 insertions(+), 9 deletions(-)

--- a/net/ieee802154/6lowpan/reassembly.c
+++ b/net/ieee802154/6lowpan/reassembly.c
@@ -410,7 +410,6 @@ int lowpan_frag_rcv(struct sk_buff *skb, u8 frag_type)
 }
 
 #ifdef CONFIG_SYSCTL
-static long zero;
 
 static struct ctl_table lowpan_frags_ns_ctl_table[] = {
 	{
@@ -427,7 +426,6 @@ static struct ctl_table lowpan_frags_ns_ctl_table[] = {
 		.maxlen		= sizeof(unsigned long),
 		.mode		= 0644,
 		.proc_handler	= proc_doulongvec_minmax,
-		.extra1		= &zero,
 		.extra2		= &init_net.ieee802154_lowpan.frags.high_thresh
 	},
 	{
--- a/net/ipv4/ip_fragment.c
+++ b/net/ipv4/ip_fragment.c
@@ -677,7 +677,7 @@ struct sk_buff *ip_check_defrag(struct net *net, struct sk_buff *skb, u32 user)
 EXPORT_SYMBOL(ip_check_defrag);
 
 #ifdef CONFIG_SYSCTL
-static long zero;
+static int dist_min;
 
 static struct ctl_table ip4_frags_ns_ctl_table[] = {
 	{
@@ -694,7 +694,6 @@ static struct ctl_table ip4_frags_ns_ctl_table[] = {
 		.maxlen		= sizeof(unsigned long),
 		.mode		= 0644,
 		.proc_handler	= proc_doulongvec_minmax,
-		.extra1		= &zero,
 		.extra2		= &init_net.ipv4.frags.high_thresh
 	},
 	{
@@ -710,7 +709,7 @@ static struct ctl_table ip4_frags_ns_ctl_table[] = {
 		.maxlen		= sizeof(int),
 		.mode		= 0644,
 		.proc_handler	= proc_dointvec_minmax,
-		.extra1		= &zero
+		.extra1		= &dist_min,
 	},
 	{ }
 };
--- a/net/ipv6/netfilter/nf_conntrack_reasm.c
+++ b/net/ipv6/netfilter/nf_conntrack_reasm.c
@@ -55,7 +55,6 @@ static const char nf_frags_cache_name[] = "nf-frags";
 static struct inet_frags nf_frags;
 
 #ifdef CONFIG_SYSCTL
-static long zero;
 
 static struct ctl_table nf_ct_frag6_sysctl_table[] = {
 	{
@@ -71,7 +70,6 @@ static struct ctl_table nf_ct_frag6_sysctl_table[] = {
 		.maxlen		= sizeof(unsigned long),
 		.mode		= 0644,
 		.proc_handler	= proc_doulongvec_minmax,
-		.extra1		= &zero,
 		.extra2		= &init_net.nf_frag.frags.high_thresh
 	},
 	{
--- a/net/ipv6/reassembly.c
+++ b/net/ipv6/reassembly.c
@@ -553,7 +553,6 @@ static const struct inet6_protocol frag_protocol = {
 };
 
 #ifdef CONFIG_SYSCTL
-static int zero;
 
 static struct ctl_table ip6_frags_ns_ctl_table[] = {
 	{
@@ -570,7 +569,6 @@ static struct ctl_table ip6_frags_ns_ctl_table[] = {
 		.maxlen		= sizeof(unsigned long),
 		.mode		= 0644,
 		.proc_handler	= proc_doulongvec_minmax,
-		.extra1		= &zero,
 		.extra2		= &init_net.ipv6.frags.high_thresh
 	},
 	{