[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, 12 insertions, 10 deletions

diff --git a/drivers/infiniband/core/cma.c b/drivers/infiniband/core/cma.c
index 9ffb9987450..2e641b255db 100644
--- a/drivers/infiniband/core/cma.c
+++ b/drivers/infiniband/core/cma.c
@@ -1866,13 +1866,14 @@ err1:
 static int cma_alloc_any_port(struct idr *ps, struct rdma_id_private *id_priv)
 {
 	struct rdma_bind_list *bind_list;
-	int port, ret;
+	int port, ret, low, high;
 
 	bind_list = kzalloc(sizeof *bind_list, GFP_KERNEL);
 	if (!bind_list)
 		return -ENOMEM;
 
 retry:
+	/* FIXME: add proper port randomization per like inet_csk_get_port */
 	do {
 		ret = idr_get_new_above(ps, bind_list, next_port, &port);
 	} while ((ret == -EAGAIN) && idr_pre_get(ps, GFP_KERNEL));
@@ -1880,18 +1881,19 @@ retry:
 	if (ret)
 		goto err1;
 
-	if (port > sysctl_local_port_range[1]) {
-		if (next_port != sysctl_local_port_range[0]) {
+	inet_get_local_port_range(&low, &high);
+	if (port > high) {
+		if (next_port != low) {
 			idr_remove(ps, port);
-			next_port = sysctl_local_port_range[0];
+			next_port = low;
 			goto retry;
 		}
 		ret = -EADDRNOTAVAIL;
 		goto err2;
 	}
 
-	if (port == sysctl_local_port_range[1])
-		next_port = sysctl_local_port_range[0];
+	if (port == high)
+		next_port = low;
 	else
 		next_port = port + 1;
 
@@ -2769,12 +2771,12 @@ static void cma_remove_one(struct ib_device *device)
 
 static int cma_init(void)
 {
-	int ret;
+	int ret, low, high;
 
 	get_random_bytes(&next_port, sizeof next_port);
-	next_port = ((unsigned int) next_port %
-		    (sysctl_local_port_range[1] - sysctl_local_port_range[0])) +
-		    sysctl_local_port_range[0];
+	inet_get_local_port_range(&low, &high);
+	next_port = ((unsigned int) next_port % (high - low)) + low;
+
 	cma_wq = create_singlethread_workqueue("rdma_cm");
 	if (!cma_wq)
 		return -ENOMEM;