Commit aeac4ec8 authored by Gleb Mazovetskiy's avatar Gleb Mazovetskiy Committed by David S. Miller
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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 4c2c8f03 ("tcp: increase source port perturb table to
2^16").

Signed-off-by: default avatarGleb Mazovetskiy <glex.spb@gmail.com>
Reviewed-by: default avatarKuniyuki Iwashima <kuniyu@amazon.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent b68777d5

net/ipv4/Kconfig

+10 −0
Original line number Diff line number Diff line
@@ -402,6 +402,16 @@ 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

net/ipv4/inet_hashtables.c

+5 −5
Original line number Diff line number Diff line
@@ -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,