inet: frags: fix ip6frag_low_thresh boundary

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>

net/ieee802154/6lowpan/reassembly.c

@@ -411,7 +411,6 @@ err:
 }
 
 #ifdef CONFIG_SYSCTL
-static long zero;
 
 static struct ctl_table lowpan_frags_ns_ctl_table[] = {
 	{
@@ -428,7 +427,6 @@ 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
 	},
 	{

net/ipv4/ip_fragment.c

@@ -667,7 +667,7 @@ 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[] = {
 	{
@@ -684,7 +684,6 @@ 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
 	},
 	{
@@ -700,7 +699,7 @@ static struct ctl_table ip4_frags_ns_ctl_table[] = {
 		.maxlen		= sizeof(int),
 		.mode		= 0644,
 		.proc_handler	= proc_dointvec_minmax,
-		.extra1		= &zero
+		.extra1		= &dist_min,
 	},
 	{ }
 };

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
 	},
 	{

net/ipv6/reassembly.c

@@ -548,7 +548,6 @@ static const struct inet6_protocol frag_protocol = {
 };
 
 #ifdef CONFIG_SYSCTL
-static int zero;
 
 static struct ctl_table ip6_frags_ns_ctl_table[] = {
 	{
@@ -565,7 +564,6 @@ 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
 	},
 	{