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From: Pablo Neira Ayuso <pablo@netfilter.org>
To: Hyunwoo Kim <imv4bel@gmail.com>
Cc: fw@strlen.de, phil@nwl.cc, davem@davemloft.net,
	edumazet@google.com, kuba@kernel.org, pabeni@redhat.com,
	horms@kernel.org, netfilter-devel@vger.kernel.org,
	coreteam@netfilter.org, netdev@vger.kernel.org
Subject: Re: [PATCH net] netfilter: ctnetlink: fix use-after-free of exp->master in expectation dump
Date: Thu, 26 Mar 2026 22:00:39 +0100	[thread overview]
Message-ID: <acWed9opPZfOIyAs@chamomile> (raw)
In-Reply-To: <aaxeXUnPpqLUURrt@v4bel>

On Sun, Mar 08, 2026 at 02:20:29AM +0900, Hyunwoo Kim wrote:
> ctnetlink_exp_dump_table() iterates the expectation hash table under
> rcu_read_lock and dereferences exp->master to access the master
> conntrack's fields (ct_net, tuplehash, ct->ext).  However, expectations
> do not hold a reference on exp->master.  A concurrent conntrack deletion
> via NFNL_SUBSYS_CTNETLINK (a different nfnetlink subsystem mutex) can
> free the master conntrack while the dump is in progress, leading to
> use-after-free on ct->ext which is freed immediately by kfree().
>
> Fix this by taking a reference on exp->master with
> refcount_inc_not_zero() before accessing it.  If the master conntrack is
> already being destroyed, skip the expectation.

For the record, ctnetlink_exp_dump_expect() does not access ct->ext
anymore since f01794106042 ("netfilter: nf_conntrack_expect: use
expect->helper"). I am archiving this proposed patch.

Thanks for reporting.

      reply	other threads:[~2026-03-26 21:00 UTC|newest]

Thread overview: 2+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2026-03-07 17:20 [PATCH net] netfilter: ctnetlink: fix use-after-free of exp->master in expectation dump Hyunwoo Kim
2026-03-26 21:00 ` Pablo Neira Ayuso [this message]

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