Hi Linus,
On Sun, Dec 09, 2018 at 07:14:05AM +0100, Linus Lüssing wrote:
> So far any changes with ebtables will reset the state of limit rules,
> leading to spikes in traffic. This is especially noticeable if changes
> are done frequently, for instance via a daemon.
>
> This patch fixes this by bailing out from (re)setting if the limit
> rule was initialized before.
>
> When sending packets every 250ms for 600s, with a
> "--limit 1/sec --limit-burst 50" rule and a command like this
> in the background:
>
> $ ebtables -N VOIDCHAIN
> $ while true; do ebtables -F VOIDCHAIN; sleep 30; done
>
> The results are:
>
> Before: ~1600 packets
> After: 650 packets
>
> This also aligns the behavior to "xtables-nft-multi ebtables" which uses
> nft_limit instead of ebt_limit. In tests nft_limit did not suffer from
> this issue and rate limited to 650 just fine.
>
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> Signed-off-by: Linus Lüssing <linus.luessing@xxxxxxxxx>
>
> ---
>
> Changelog v2:
>
> - Adjusted commit message (adjusted title, added test results with
> nft_limit for comparison)
> - Excluded rate limiting variables from zeroing when passed to userspace
> by increasing .usersize. This became necessary with 4.11 /
> commit ec2318904965 ("xtables: extend matches and targets with .usersize")
> - Retested with 4.20-rc4 and current net-next/master (83af01ba1c2d)
>
> v1 was:
>
> "[net-next] bridge: ebtables: Avoid resetting limit rule state"
> -> https://lore.kernel.org/patchwork/patch/854802/
> ---
> net/bridge/netfilter/ebt_limit.c | 6 +++++-
> 1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/net/bridge/netfilter/ebt_limit.c b/net/bridge/netfilter/ebt_limit.c
> index 165b9d678cf1..2cf9861c3bce 100644
> --- a/net/bridge/netfilter/ebt_limit.c
> +++ b/net/bridge/netfilter/ebt_limit.c
> @@ -69,6 +69,10 @@ static int ebt_limit_mt_check(const struct xt_mtchk_param *par)
> {
> struct ebt_limit_info *info = par->matchinfo;
>
> + /* Do not reset state on unrelated table changes */
> + if (info->prev)
> + return 0;
Hm, still I don't think we can follow this path, even if it works.
This means we trust userspace in what it sets for info->prev.
Using ebtables-nft (instead of ebtables-legacy) fixes this problem,
without this patch.
> +
> /* Check for overflow. */
> if (info->burst == 0 ||
> user2credits(info->avg * info->burst) < user2credits(info->avg)) {
> @@ -105,7 +109,7 @@ static struct xt_match ebt_limit_mt_reg __read_mostly = {
> .match = ebt_limit_mt,
> .checkentry = ebt_limit_mt_check,
> .matchsize = sizeof(struct ebt_limit_info),
> - .usersize = offsetof(struct ebt_limit_info, prev),
> + .usersize = sizeof(struct ebt_limit_info),
> #ifdef CONFIG_COMPAT
> .compatsize = sizeof(struct ebt_compat_limit_info),
> #endif
> --
> 2.11.0
>
