[PATCH net-next 2/2] inet: frags: fix ip6frag_low_thresh boundary

[PATCH net-next 2/2] inet: frags: fix ip6frag_low_thresh boundary

[Eric Dumazet]

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>
---
 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(-)

diff --git a/net/ieee802154/6lowpan/reassembly.c b/net/ieee802154/6lowpan/reassembly.c
index 44f148a6bb57bb737c35a07e3f070472e209ea23..1790b65944b3ee188608b1a76d4f9a42fb1479d5 100644
--- a/net/ieee802154/6lowpan/reassembly.c
+++ b/net/ieee802154/6lowpan/reassembly.c
@@ -411,7 +411,6 @@ 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[] = {
 	{
@@ -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
 	},
 	{
diff --git a/net/ipv4/ip_fragment.c b/net/ipv4/ip_fragment.c
index 994fa70a910f472ebecc336ddd62d1442014eaba..8e9528ebaa8e1af91172466cc161a83301a217ca 100644
--- a/net/ipv4/ip_fragment.c
+++ b/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,
 	},
 	{ }
 };
diff --git a/net/ipv6/netfilter/nf_conntrack_reasm.c b/net/ipv6/netfilter/nf_conntrack_reasm.c
index 3622aac343aea3cd0d8165d8681f42595735cd90..5e0332014c1738999e680c1853829f384e880284 100644
--- 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
 	},
 	{
diff --git a/net/ipv6/reassembly.c b/net/ipv6/reassembly.c
index 70e4a578b2fb6b2941daeebe4f476214953db047..4979610287e262a873b807a06ac980a17cd1101b 100644
--- a/net/ipv6/reassembly.c
+++ b/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
 	},
 	{
-- 
2.17.0.484.g0c8726318c-goog

Re: [PATCH net-next 2/2] inet: frags: fix ip6frag_low_thresh boundary

[Eric Dumazet]

On 04/04/2018 08:35 AM, Eric Dumazet wrote:
> 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>

David, please ignore the net-next 2/2 in the title, there is a single patch, targeting net tree,
sorry for the confusion.

Re: [PATCH net-next 2/2] inet: frags: fix ip6frag_low_thresh boundary

[David Miller]

From: Eric Dumazet <edumazet@google.com>
Date: Wed,  4 Apr 2018 08:35:10 -0700

> 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>

Applied, thanks Eric.