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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Reindl Harald <h.reindl@thelounge.net>,
        Jozsef Kadlecsik <kadlec@netfilter.org>,
        Pablo Neira Ayuso <pablo@netfilter.org>,
        Sasha Levin <sashal@kernel.org>
Subject: [PATCH 5.4 29/60] netfilter: xt_recent: Fix attempt to update deleted entry
Date:   Mon, 15 Feb 2021 16:27:17 +0100
Message-Id: <20210215152716.285572820@linuxfoundation.org>
In-Reply-To: <20210215152715.401453874@linuxfoundation.org>
References: <20210215152715.401453874@linuxfoundation.org>
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From: Jozsef Kadlecsik <kadlec@mail.kfki.hu>

[ Upstream commit b1bdde33b72366da20d10770ab7a49fe87b5e190 ]

When both --reap and --update flag are specified, there's a code
path at which the entry to be updated is reaped beforehand,
which then leads to kernel crash. Reap only entries which won't be
updated.

Fixes kernel bugzilla #207773.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=207773
Reported-by: Reindl Harald <h.reindl@thelounge.net>
Fixes: 0079c5aee348 ("netfilter: xt_recent: add an entry reaper")
Signed-off-by: Jozsef Kadlecsik <kadlec@netfilter.org>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 net/netfilter/xt_recent.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/net/netfilter/xt_recent.c b/net/netfilter/xt_recent.c
index 6c2582a197667..3469b60736103 100644
--- a/net/netfilter/xt_recent.c
+++ b/net/netfilter/xt_recent.c
@@ -152,7 +152,8 @@ static void recent_entry_remove(struct recent_table *t, struct recent_entry *e)
 /*
  * Drop entries with timestamps older then 'time'.
  */
-static void recent_entry_reap(struct recent_table *t, unsigned long time)
+static void recent_entry_reap(struct recent_table *t, unsigned long time,
+			      struct recent_entry *working, bool update)
 {
 	struct recent_entry *e;
 
@@ -161,6 +162,12 @@ static void recent_entry_reap(struct recent_table *t, unsigned long time)
 	 */
 	e = list_entry(t->lru_list.next, struct recent_entry, lru_list);
 
+	/*
+	 * Do not reap the entry which are going to be updated.
+	 */
+	if (e == working && update)
+		return;
+
 	/*
 	 * The last time stamp is the most recent.
 	 */
@@ -303,7 +310,8 @@ recent_mt(const struct sk_buff *skb, struct xt_action_param *par)
 
 		/* info->seconds must be non-zero */
 		if (info->check_set & XT_RECENT_REAP)
-			recent_entry_reap(t, time);
+			recent_entry_reap(t, time, e,
+				info->check_set & XT_RECENT_UPDATE && ret);
 	}
 
 	if (info->check_set & XT_RECENT_SET ||
-- 
2.27.0