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tcp: configurable source port perturb table size

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[ 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>
This commit is contained in:
Gleb Mazovetskiy 2022-11-14 22:56:16 +00:00 committed by Greg Kroah-Hartman
parent 07da8fca30
commit 86136bf623
2 changed files with 15 additions and 5 deletions
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10
net/ipv4/Kconfig
View File

@ -389,6 +389,16 @@ 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

10
net/ipv4/inet_hashtables.c
View File

@ -675,13 +675,13 @@ 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,