1 files changed, 22 insertions, 6 deletions

diff --git a/net/ipv4/inet_hashtables.c b/net/ipv4/inet_hashtables.c
index 1346e45cf8d1..1ebad5a024a7 100644
--- a/net/ipv4/inet_hashtables.c
+++ b/net/ipv4/inet_hashtables.c
@@ -389,7 +389,7 @@ not_unique:
 	return -EADDRNOTAVAIL;
 }
 
-static u32 inet_sk_port_offset(const struct sock *sk)
+static u64 inet_sk_port_offset(const struct sock *sk)
 {
 	const struct inet_sock *inet = inet_sk(sk);
 
@@ -587,8 +587,19 @@ void inet_unhash(struct sock *sk)
 }
 EXPORT_SYMBOL_GPL(inet_unhash);
 
+/* RFC 6056 3.3.4.  Algorithm 4: Double-Hash Port Selection Algorithm
+ * Note that we use 32bit integers (vs RFC 'short integers')
+ * because 2^16 is not a multiple of num_ephemeral and this
+ * property might be used by clever attacker.
+ * RFC claims using TABLE_LENGTH=10 buckets gives an improvement,
+ * we use 256 instead to really give more isolation and
+ * privacy, this only consumes 1 KB of kernel memory.
+ */
+#define INET_TABLE_PERTURB_SHIFT 8
+static u32 table_perturb[1 << INET_TABLE_PERTURB_SHIFT];
+
 int __inet_hash_connect(struct inet_timewait_death_row *death_row,
-		struct sock *sk, u32 port_offset,
+		struct sock *sk, u64 port_offset,
 		int (*check_established)(struct inet_timewait_death_row *,
 			struct sock *, __u16, struct inet_timewait_sock **))
 {
@@ -600,7 +611,7 @@ int __inet_hash_connect(struct inet_timewait_death_row *death_row,
 	struct inet_bind_bucket *tb;
 	u32 remaining, offset;
 	int ret, i, low, high;
-	static u32 hint;
+	u32 index;
 
 	if (port) {
 		head = &hinfo->bhash[inet_bhashfn(net, port,
@@ -625,7 +636,12 @@ int __inet_hash_connect(struct inet_timewait_death_row *death_row,
 	if (likely(remaining > 1))
 		remaining &= ~1U;
 
-	offset = (hint + port_offset) % remaining;
+	net_get_random_once(table_perturb, sizeof(table_perturb));
+	index = hash_32(port_offset, INET_TABLE_PERTURB_SHIFT);
+
+	offset = READ_ONCE(table_perturb[index]) + port_offset;
+	offset %= remaining;
+
 	/* In first pass we try ports of @low parity.
 	 * inet_csk_get_port() does the opposite choice.
 	 */
@@ -678,7 +694,7 @@ next_port:
 	return -EADDRNOTAVAIL;
 
 ok:
-	hint += i + 2;
+	WRITE_ONCE(table_perturb[index], READ_ONCE(table_perturb[index]) + i + 2);
 
 	/* Head lock still held and bh's disabled */
 	inet_bind_hash(sk, tb, port);
@@ -701,7 +717,7 @@ ok:
 int inet_hash_connect(struct inet_timewait_death_row *death_row,
 		      struct sock *sk)
 {
-	u32 port_offset = 0;
+	u64 port_offset = 0;
 
 	if (!inet_sk(sk)->inet_num)
 		port_offset = inet_sk_port_offset(sk);