linux-kernel - [PATCH 5.15 120/124] netfilter: nft_ct: fix use after free when attaching zone template

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Message-Id: <20220426081750.701058603@linuxfoundation.org>
Date:   Tue, 26 Apr 2022 10:22:01 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, kernel test robot <oliver.sang@...el.com>,
        Florian Westphal <fw@...len.de>,
        Pablo Neira Ayuso <pablo@...filter.org>
Subject: [PATCH 5.15 120/124] netfilter: nft_ct: fix use after free when attaching zone template

From: Florian Westphal <fw@...len.de>

commit 34243b9ec856309339172b1507379074156947e8 upstream.

The conversion erroneously removed the refcount increment.
In case we can use the percpu template, we need to increment
the refcount, else it will be released when the skb gets freed.

In case the slowpath is taken, the new template already has a
refcount of 1.

Fixes: 719774377622 ("netfilter: conntrack: convert to refcount_t api")
Reported-by: kernel test robot <oliver.sang@...el.com>
Signed-off-by: Florian Westphal <fw@...len.de>
Signed-off-by: Pablo Neira Ayuso <pablo@...filter.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 net/netfilter/nft_ct.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

--- a/net/netfilter/nft_ct.c
+++ b/net/netfilter/nft_ct.c
@@ -260,9 +260,12 @@ static void nft_ct_set_zone_eval(const s
 	ct = this_cpu_read(nft_ct_pcpu_template);
 
 	if (likely(refcount_read(&ct->ct_general.use) == 1)) {
+		refcount_inc(&ct->ct_general.use);
 		nf_ct_zone_add(ct, &zone);
 	} else {
-		/* previous skb got queued to userspace */
+		/* previous skb got queued to userspace, allocate temporary
+		 * one until percpu template can be reused.
+		 */
 		ct = nf_ct_tmpl_alloc(nft_net(pkt), &zone, GFP_ATOMIC);
 		if (!ct) {
 			regs->verdict.code = NF_DROP;