netdev - Re: [PATCH net] net: ipv4: avoid mixed n_redirects and rate

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Message-Id: <20191004.172808.542472286230604033.davem@davemloft.net>
Date:   Fri, 04 Oct 2019 17:28:08 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     pabeni@...hat.com
Cc:     netdev@...r.kernel.org, lbianconi@...hat.com, xmu@...hat.com
Subject: Re: [PATCH net] net: ipv4: avoid mixed n_redirects and rate_tokens
 usage

From: Paolo Abeni <pabeni@...hat.com>
Date: Fri,  4 Oct 2019 15:11:17 +0200

> Since commit c09551c6ff7f ("net: ipv4: use a dedicated counter
> for icmp_v4 redirect packets") we use 'n_redirects' to account
> for redirect packets, but we still use 'rate_tokens' to compute
> the redirect packets exponential backoff.
> 
> If the device sent to the relevant peer any ICMP error packet
> after sending a redirect, it will also update 'rate_token' according
> to the leaking bucket schema; typically 'rate_token' will raise
> above BITS_PER_LONG and the redirect packets backoff algorithm
> will produce undefined behavior.
> 
> Fix the issue using 'n_redirects' to compute the exponential backoff
> in ip_rt_send_redirect().
> 
> Note that we still clear rate_tokens after a redirect silence period,
> to avoid changing an established behaviour.
> 
> The root cause predates git history; before the mentioned commit in
> the critical scenario, the kernel stopped sending redirects, after
> the mentioned commit the behavior more randomic.
> 
> Reported-by: Xiumei Mu <xmu@...hat.com>
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> Fixes: c09551c6ff7f ("net: ipv4: use a dedicated counter for icmp_v4 redirect packets")
> Signed-off-by: Paolo Abeni <pabeni@...hat.com>

Applied and queued up for -stable.