netdev - Re: [PATCH net] net: ipv4: really enforce backoff for redirects

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Message-ID: <20200508225704.40f53162@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Fri, 8 May 2020 22:57:04 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Paolo Abeni <pabeni@...hat.com>
Cc:     netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
        Colin Walters <walters@...hat.com>
Subject: Re: [PATCH net] net: ipv4: really enforce backoff for redirects

On Fri,  8 May 2020 19:28:34 +0200 Paolo Abeni wrote:
> In commit b406472b5ad7 ("net: ipv4: avoid mixed n_redirects and
> rate_tokens usage") I missed the fact that a 0 'rate_tokens' will
> bypass the backoff algorithm.
> 
> Since rate_tokens is cleared after a redirect silence, and never
> incremented on redirects, if the host keeps receiving packets
> requiring redirect it will reply ignoring the backoff.
> 
> Additionally, the 'rate_last' field will be updated with the
> cadence of the ingress packet requiring redirect. If that rate is
> high enough, that will prevent the host from generating any
> other kind of ICMP messages
> 
> The check for a zero 'rate_tokens' value was likely a shortcut
> to avoid the more complex backoff algorithm after a redirect
> silence period. Address the issue checking for 'n_redirects'
> instead, which is incremented on successful redirect, and
> does not interfere with other ICMP replies.
> 
> Fixes: b406472b5ad7 ("net: ipv4: avoid mixed n_redirects and rate_tokens usage")

Looks like this one got backported all the way back to 3.16..

> Reported-and-tested-by: Colin Walters <walters@...hat.com>
> Signed-off-by: Paolo Abeni <pabeni@...hat.com>

Applied, thanks!