net:rfs: adjust table size checking

Make sure root user does not try something stupid.

Also make sure mask field in struct rps_sock_flow_table
does not share a cache line with the potentially often dirtied
flow table.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Fixes: 567e4b79 ("net: rfs: add hash collision detection")
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/netdevice.h

@@ -653,7 +653,8 @@ struct rps_dev_flow_table {
  */
 struct rps_sock_flow_table {
 	u32	mask;
-	u32	ents[0];
+
+	u32	ents[0] ____cacheline_aligned_in_smp;
 };
 #define	RPS_SOCK_FLOW_TABLE_SIZE(_num) (offsetof(struct rps_sock_flow_table, ents[_num]))
 

net/core/sysctl_net_core.c

@@ -52,7 +52,7 @@ static int rps_sock_flow_sysctl(struct ctl_table *table, int write,
 
 	if (write) {
 		if (size) {
-			if (size > 1<<30) {
+			if (size > 1<<29) {
 				/* Enforce limit to prevent overflow */
 				mutex_unlock(&sock_flow_mutex);
 				return -EINVAL;