tcp: configurable source port perturb table size

[ Upstream commit aeac4ec8f46d610a10adbaeff5e2edf6a88ffc62 ]

On embedded systems with little memory and no relevant
security concerns, it is beneficial to reduce the size
of the table.

Reducing the size from 2^16 to 2^8 saves 255 KiB
of kernel RAM.

Makes the table size configurable as an expert option.

The size was previously increased from 2^8 to 2^16
in commit 4c2c8f03a5ab ("tcp: increase source port perturb table to
2^16").

Signed-off-by: Gleb Mazovetskiy <glex.spb@gmail.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/net/ipv4/Kconfig b/net/ipv4/Kconfig
index 87983e70f03f320fffae872a13f6befb34467204..23b06063e1a512b69d437f3e9ae74ff37e03664b 100644 (file)
--- a/net/ipv4/Kconfig
+++ b/net/ipv4/Kconfig
@@ -403,6 +403,16 @@ config INET_IPCOMP
 
          If unsure, say Y.
 
+config INET_TABLE_PERTURB_ORDER
+       int "INET: Source port perturbation table size (as power of 2)" if EXPERT
+       default 16
+       help
+         Source port perturbation table size (as power of 2) for
+         RFC 6056 3.3.4.  Algorithm 4: Double-Hash Port Selection Algorithm.
+
+         The default is almost always what you want.
+         Only change this if you know what you are doing.
+
 config INET_XFRM_TUNNEL
        tristate
        select INET_TUNNEL

diff --git a/net/ipv4/inet_hashtables.c b/net/ipv4/inet_hashtables.c
index ce6a3873f89e3c1979816c90523b3e9692cb7d0d..0d378da4b1b1add01c41140631ff8dfa7f7b9500 100644 (file)
--- a/net/ipv4/inet_hashtables.c
+++ b/net/ipv4/inet_hashtables.c
@@ -721,13 +721,13 @@ EXPORT_SYMBOL_GPL(inet_unhash);
  * 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, though
- * attacks were since demonstrated, thus we use 65536 instead to really
- * give more isolation and privacy, at the expense of 256kB of kernel
- * memory.
+ * attacks were since demonstrated, thus we use 65536 by default instead
+ * to really give more isolation and privacy, at the expense of 256kB
+ * of kernel memory.
  */
-#define INET_TABLE_PERTURB_SHIFT 16
-#define INET_TABLE_PERTURB_SIZE (1 << INET_TABLE_PERTURB_SHIFT)
+#define INET_TABLE_PERTURB_SIZE (1 << CONFIG_INET_TABLE_PERTURB_ORDER)
 static u32 *table_perturb;
 
 int __inet_hash_connect(struct inet_timewait_death_row *death_row,