netdev - [PATCH net 1/4] netfilter: xt_recent: Fix attempt to update deleted entry

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Message-Id: <20210205001727.2125-2-pablo@netfilter.org>
Date:   Fri,  5 Feb 2021 01:17:24 +0100
From:   Pablo Neira Ayuso <pablo@...filter.org>
To:     netfilter-devel@...r.kernel.org
Cc:     davem@...emloft.net, netdev@...r.kernel.org, kuba@...nel.org
Subject: [PATCH net 1/4] netfilter: xt_recent: Fix attempt to update deleted entry

From: Jozsef Kadlecsik <kadlec@...l.kfki.hu>

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@...lounge.net>
Fixes: 0079c5aee348 ("netfilter: xt_recent: add an entry reaper")
Signed-off-by: Jozsef Kadlecsik <kadlec@...filter.org>
Signed-off-by: Pablo Neira Ayuso <pablo@...filter.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 606411869698..0446307516cd 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 ||
-- 
2.20.1