[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, 3 insertions, 3 deletions

diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index ef4d901ee9a..cb9fc58efb2 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -147,11 +147,11 @@ int __udp_lib_get_port(struct sock *sk, unsigned short snum,
 	write_lock_bh(&udp_hash_lock);
 
 	if (!snum) {
-		int i;
-		int low = sysctl_local_port_range[0];
-		int high = sysctl_local_port_range[1];
+		int i, low, high;
 		unsigned rover, best, best_size_so_far;
 
+		inet_get_local_port_range(&low, &high);
+
 		best_size_so_far = UINT_MAX;
 		best = rover = net_random() % (high - low) + low;