[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, 6 insertions, 7 deletions

diff --git a/net/ipv4/inet_hashtables.c b/net/ipv4/inet_hashtables.c
index fb662621c54..fac6398e436 100644
--- a/net/ipv4/inet_hashtables.c
+++ b/net/ipv4/inet_hashtables.c
@@ -279,19 +279,18 @@ int inet_hash_connect(struct inet_timewait_death_row *death_row,
         int ret;
 
         if (!snum) {
-                int low = sysctl_local_port_range[0];
-                int high = sysctl_local_port_range[1];
-                int range = high - low;
-                int i;
-                int port;
+                int i, remaining, low, high, port;
                 static u32 hint;
                 u32 offset = hint + inet_sk_port_offset(sk);
                 struct hlist_node *node;
                 struct inet_timewait_sock *tw = NULL;
 
+                inet_get_local_port_range(&low, &high);
+                remaining = high - low;
+
                 local_bh_disable();
-                for (i = 1; i <= range; i++) {
-                        port = low + (i + offset) % range;
+                for (i = 1; i <= remaining; i++) {
+                        port = low + (i + offset) % remaining;
                         head = &hinfo->bhash[inet_bhashfn(port, hinfo->bhash_size)];
                         spin_lock(&head->lock);