tcp: configurable source port perturb table size

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>

1 files changed, 5 insertions, 5 deletions

diff --git a/net/ipv4/inet_hashtables.c b/net/ipv4/inet_hashtables.c
index d3dc28156622..033bf3c2538f 100644
--- a/net/ipv4/inet_hashtables.c
+++ b/net/ipv4/inet_hashtables.c
@@ -906,13 +906,13 @@ EXPORT_SYMBOL_GPL(inet_bhash2_update_saddr);
  * 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,