[PATCH] netfilter: Fix attempt to update deleted entry in xt_recent

[PATCH] netfilter: Fix attempt to update deleted entry in xt_recent

[Jozsef Kadlecsik]

Hi Pablo,

Please review the next patch and consider applying it in the nf branch:

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.

Reported by Reindl Harald.

Signed-off-by: Jozsef Kadlecsik <kadlec@netfilter.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

Best regards,
Jozsef
-
E-mail  : kadlec@blackhole.kfki.hu, kadlecsik.jozsef@wigner.hu
PGP key : https://wigner.hu/~kadlec/pgp_public_key.txt
Address : Wigner Research Centre for Physics
          H-1525 Budapest 114, POB. 49, Hungary

Re: [PATCH] netfilter: Fix attempt to update deleted entry in xt_recent

[Pablo Neira Ayuso]

On Fri, Jan 29, 2021 at 08:57:43PM +0100, Jozsef Kadlecsik wrote:
> Hi Pablo,
> 
> Please review the next patch and consider applying it in the nf branch:
> 
> 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.

Applied, thanks Jozsef.