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    Subject[PATCH AUTOSEL 4.19 07/11] tcp: configurable source port perturb table size
    Date
    From: Gleb Mazovetskiy <glex.spb@gmail.com>

    [ 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>
    ---
    net/ipv4/Kconfig | 10 ++++++++++
    net/ipv4/inet_hashtables.c | 10 +++++-----
    2 files changed, 15 insertions(+), 5 deletions(-)

    diff --git a/net/ipv4/Kconfig b/net/ipv4/Kconfig
    index 2e12f848203a..8acfa1487478 100644
    --- a/net/ipv4/Kconfig
    +++ b/net/ipv4/Kconfig
    @@ -388,6 +388,16 @@ 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 70070f1003a0..3c58019f0718 100644
    --- a/net/ipv4/inet_hashtables.c
    +++ b/net/ipv4/inet_hashtables.c
    @@ -718,13 +718,13 @@ 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,
    --
    2.35.1
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