net: limit tcp/udp rmem/wmem to SOCK_{RCV,SND}BUF_MIN

This is similar to b1cb59cf(net: sysctl_net_core: check SNDBUF
and RCVBUF for min length). I don't think too small values can cause
crashes in the case of udp and tcp, but I've seen this set to too
small values which triggered awful performance. It also makes the
setting consistent across all the wmem/rmem sysctls.
Signed-off-by: NSorin Dumitru <sdumitru@ixiacom.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv4/sysctl_net_ipv4.c

@@ -41,6 +41,8 @@ static int tcp_syn_retries_min = 1;
 static int tcp_syn_retries_max = MAX_TCP_SYNCNT;
 static int ip_ping_group_range_min[] = { 0, 0 };
 static int ip_ping_group_range_max[] = { GID_T_MAX, GID_T_MAX };
+static int min_sndbuf = SOCK_MIN_SNDBUF;
+static int min_rcvbuf = SOCK_MIN_RCVBUF;
 
 /* Update system visible IP port range */
 static void set_local_port_range(struct net *net, int range[2])
@@ -528,7 +530,7 @@ static struct ctl_table ipv4_table[] = {
 		.maxlen		= sizeof(sysctl_tcp_wmem),
 		.mode		= 0644,
 		.proc_handler	= proc_dointvec_minmax,
-		.extra1		= &one,
+		.extra1		= &min_sndbuf,
 	},
 	{
 		.procname	= "tcp_notsent_lowat",
@@ -543,7 +545,7 @@ static struct ctl_table ipv4_table[] = {
 		.maxlen		= sizeof(sysctl_tcp_rmem),
 		.mode		= 0644,
 		.proc_handler	= proc_dointvec_minmax,
-		.extra1		= &one,
+		.extra1		= &min_rcvbuf,
 	},
 	{
 		.procname	= "tcp_app_win",
@@ -756,7 +758,7 @@ static struct ctl_table ipv4_table[] = {
 		.maxlen		= sizeof(sysctl_udp_rmem_min),
 		.mode		= 0644,
 		.proc_handler	= proc_dointvec_minmax,
-		.extra1		= &one
+		.extra1		= &min_rcvbuf,
 	},
 	{
 		.procname	= "udp_wmem_min",
@@ -764,7 +766,7 @@ static struct ctl_table ipv4_table[] = {
 		.maxlen		= sizeof(sysctl_udp_wmem_min),
 		.mode		= 0644,
 		.proc_handler	= proc_dointvec_minmax,
-		.extra1		= &one
+		.extra1		= &min_sndbuf,
 	},
 	{ }
 };