linux-kernel - Re: [PATCH] netfilter: conntrack: drop expectations before freeing templates

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Message-ID: <aKUUBsFYBYOu2xu-@strlen.de>
Date: Wed, 20 Aug 2025 02:17:10 +0200
From: Florian Westphal <fw@...len.de>
To: Qingjie Xing <xqjcool@...il.com>
Cc: linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	netfilter-devel@...r.kernel.org
Subject: Re: [PATCH] netfilter: conntrack: drop expectations before freeing
 templates

Qingjie Xing <xqjcool@...il.com> wrote:
> With an iptables-configured TFTP helper in place, a UDP packet 
> (10.65.41.36:1069 → 10.65.36.2:69, TFTP RRQ) triggered creation of an expectation.
> Later, iptables changes removed the rule’s per-rule template nf_conn. 
> When the expectation’s timer expired, nf_ct_unlink_expect_report() 
> ran and dereferenced the freed master, causing a crash.

Sorry, I do not see the problem.
A template should never be listed as exp->master.

Can you make a reproducer/selftest for this bug?

I worry we paper over a different bug.