[INET]: local port range robustness

Expansion of original idea from Denis V. Lunev <den@openvz.org>

Add robustness and locking to the local_port_range sysctl.
1. Enforce that low < high when setting.
2. Use seqlock to ensure atomic update.

The locking might seem like overkill, but there are
cases where sysadmin might want to change value in the
middle of a DoS attack.

Signed-off-by: Stephen Hemminger <shemminger@linux-foundation.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 71 insertions, 4 deletions

diff --git a/net/ipv4/sysctl_net_ipv4.c b/net/ipv4/sysctl_net_ipv4.c
index 53ef0f4bbdaa..eb286abcf5dc 100644
--- a/net/ipv4/sysctl_net_ipv4.c
+++ b/net/ipv4/sysctl_net_ipv4.c
@@ -12,6 +12,7 @@
 #include <linux/sysctl.h>
 #include <linux/igmp.h>
 #include <linux/inetdevice.h>
+#include <linux/seqlock.h>
 #include <net/snmp.h>
 #include <net/icmp.h>
 #include <net/ip.h>
@@ -89,6 +90,74 @@ static int ipv4_sysctl_forward_strategy(ctl_table *table,
 	return 1;
 }
 
+extern seqlock_t sysctl_port_range_lock;
+extern int sysctl_local_port_range[2];
+
+/* Update system visible IP port range */
+static void set_local_port_range(int range[2])
+{
+	write_seqlock(&sysctl_port_range_lock);
+	sysctl_local_port_range[0] = range[0];
+	sysctl_local_port_range[1] = range[1];
+	write_sequnlock(&sysctl_port_range_lock);
+}
+
+/* Validate changes from /proc interface. */
+static int ipv4_local_port_range(ctl_table *table, int write, struct file *filp,
+				 void __user *buffer,
+				 size_t *lenp, loff_t *ppos)
+{
+	int ret;
+	int range[2] = { sysctl_local_port_range[0],
+			 sysctl_local_port_range[1] };
+	ctl_table tmp = {
+		.data = &range,
+		.maxlen = sizeof(range),
+		.mode = table->mode,
+		.extra1 = &ip_local_port_range_min,
+		.extra2 = &ip_local_port_range_max,
+	};
+
+	ret = proc_dointvec_minmax(&tmp, write, filp, buffer, lenp, ppos);
+
+	if (write && ret == 0) {
+		if (range[1] <= range[0])
+			ret = -EINVAL;
+		else
+			set_local_port_range(range);
+	}
+
+	return ret;
+}
+
+/* Validate changes from sysctl interface. */
+static int ipv4_sysctl_local_port_range(ctl_table *table, int __user *name,
+					 int nlen, void __user *oldval,
+					 size_t __user *oldlenp,
+					void __user *newval, size_t newlen)
+{
+	int ret;
+	int range[2] = { sysctl_local_port_range[0],
+			 sysctl_local_port_range[1] };
+	ctl_table tmp = {
+		.data = &range,
+		.maxlen = sizeof(range),
+		.mode = table->mode,
+		.extra1 = &ip_local_port_range_min,
+		.extra2 = &ip_local_port_range_max,
+	};
+
+	ret = sysctl_intvec(&tmp, name, nlen, oldval, oldlenp, newval, newlen);
+	if (ret == 0 && newval && newlen) {
+		if (range[1] <= range[0])
+			ret = -EINVAL;
+		else
+			set_local_port_range(range);
+	}
+	return ret;
+}
+
+
 static int proc_tcp_congestion_control(ctl_table *ctl, int write, struct file * filp,
 				       void __user *buffer, size_t *lenp, loff_t *ppos)
 {
@@ -427,10 +496,8 @@ ctl_table ipv4_table[] = {
 		.data		= &sysctl_local_port_range,
 		.maxlen		= sizeof(sysctl_local_port_range),
 		.mode		= 0644,
-		.proc_handler	= &proc_dointvec_minmax,
-		.strategy	= &sysctl_intvec,
-		.extra1		= ip_local_port_range_min,
-		.extra2		= ip_local_port_range_max
+		.proc_handler	= &ipv4_local_port_range,
+		.strategy	= &ipv4_sysctl_local_port_range,
 	},
 	{
 		.ctl_name	= NET_IPV4_ICMP_ECHO_IGNORE_ALL,