netdev - [PATCH 6/6] netfilter: xt_hashlimit: unregister proc file before releasing mutex

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Message-Id: <20200226225442.9598-7-pablo@netfilter.org>
Date:   Wed, 26 Feb 2020 23:54:42 +0100
From:   Pablo Neira Ayuso <pablo@...filter.org>
To:     netfilter-devel@...r.kernel.org
Cc:     davem@...emloft.net, netdev@...r.kernel.org
Subject: [PATCH 6/6] netfilter: xt_hashlimit: unregister proc file before releasing mutex

From: Cong Wang <xiyou.wangcong@...il.com>

Before releasing the global mutex, we only unlink the hashtable
from the hash list, its proc file is still not unregistered at
this point. So syzbot could trigger a race condition where a
parallel htable_create() could register the same file immediately
after the mutex is released.

Move htable_remove_proc_entry() back to mutex protection to
fix this. And, fold htable_destroy() into htable_put() to make
the code slightly easier to understand.

Reported-and-tested-by: syzbot+d195fd3b9a364ddd6731@...kaller.appspotmail.com
Fixes: c4a3922d2d20 ("netfilter: xt_hashlimit: reduce hashlimit_mutex scope for htable_put()")
Signed-off-by: Cong Wang <xiyou.wangcong@...il.com>
Signed-off-by: Pablo Neira Ayuso <pablo@...filter.org>
---
 net/netfilter/xt_hashlimit.c | 16 ++++++----------
 1 file changed, 6 insertions(+), 10 deletions(-)

diff --git a/net/netfilter/xt_hashlimit.c b/net/netfilter/xt_hashlimit.c
index 7a2c4b8408c4..8c835ad63729 100644
--- a/net/netfilter/xt_hashlimit.c
+++ b/net/netfilter/xt_hashlimit.c
@@ -402,15 +402,6 @@ static void htable_remove_proc_entry(struct xt_hashlimit_htable *hinfo)
 		remove_proc_entry(hinfo->name, parent);
 }
 
-static void htable_destroy(struct xt_hashlimit_htable *hinfo)
-{
-	cancel_delayed_work_sync(&hinfo->gc_work);
-	htable_remove_proc_entry(hinfo);
-	htable_selective_cleanup(hinfo, true);
-	kfree(hinfo->name);
-	vfree(hinfo);
-}
-
 static struct xt_hashlimit_htable *htable_find_get(struct net *net,
 						   const char *name,
 						   u_int8_t family)
@@ -432,8 +423,13 @@ static void htable_put(struct xt_hashlimit_htable *hinfo)
 {
 	if (refcount_dec_and_mutex_lock(&hinfo->use, &hashlimit_mutex)) {
 		hlist_del(&hinfo->node);
+		htable_remove_proc_entry(hinfo);
 		mutex_unlock(&hashlimit_mutex);
-		htable_destroy(hinfo);
+
+		cancel_delayed_work_sync(&hinfo->gc_work);
+		htable_selective_cleanup(hinfo, true);
+		kfree(hinfo->name);
+		vfree(hinfo);
 	}
 }
 
-- 
2.11.0