From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 7632D3F6619; Wed, 20 May 2026 18:03:31 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779300212; cv=none; b=ZGaT6YZUli4W+2sMMP21GQS39ZyhabTsEEmsTt4S2h6tAVpiXgS+qWCfWVC4w+z3V7O6BQ9GFEo6F99BY3Kdp1lydoD6Y+wSiyqpxDDlgPEDWvFaoIeYANBJbwVHLF5Jxqg8cs8c0e6s+PwSlwDyAFkH8w3FOHy3LxFpRxi3NcQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779300212; c=relaxed/simple; bh=7ET3afKGSxH9dULYBc9Q3iCW5DNsLHdmzRFoLqvAFvI=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=AjSyRM9bZ5AXM4qebZhnKck0/DAWl0uaocUvRVOQNIPis77XjBJsmMqh4giv+BkObwJVCCg+pC5gcvL/wdVqTWwD4YGsjcJ+hfTbBZ9UdvsJ+wN4xFJ4ud0NzbNkC/92CZQPKRi76QjwO6IYfXj/XPt3vrz215R8eShwP8RKoWE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=o6b5BHs+; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="o6b5BHs+" Received: by smtp.kernel.org (Postfix) with ESMTPSA id DCE581F00893; Wed, 20 May 2026 18:03:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1779300211; bh=8Hm1fsPuSvb1zCxUwCyjA8kXC2tWxZZbVya6oiVyTvU=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=o6b5BHs+Qn5xgllckNwDi0v2jdK09Bw6EOXZ4AkIIdkLn86IS6GAMvpAtIEBCp4xq VEQmroen9pSqvMiVYSjJmMaHvfTp2V8zMgxe5FdIaXEidrhK5RexwMuqWFzXdI6lF4 ZefiIundEovrWajxQWHYnhTDxr6h9XCYIezjYY+M= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, zdi-disclosures@trendmicro.com, Victor Nogueira , Jamal Hadi Salim , Jakub Kicinski , Sasha Levin Subject: [PATCH 6.12 090/666] net/sched: act_ct: Only release RCU read lock after ct_ft Date: Wed, 20 May 2026 18:15:01 +0200 Message-ID: <20260520162113.177766746@linuxfoundation.org> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20260520162111.222830634@linuxfoundation.org> References: <20260520162111.222830634@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.12-stable review patch. If anyone has any objections, please let me know. ------------------ From: Jamal Hadi Salim [ Upstream commit f462dca0c8415bf0058d0ffa476354c4476d0f09 ] When looking up a flow table in act_ct in tcf_ct_flow_table_get(), rhashtable_lookup_fast() internally opens and closes an RCU read critical section before returning ct_ft. The tcf_ct_flow_table_cleanup_work() can complete before refcount_inc_not_zero() is invoked on the returned ct_ft resulting in a UAF on the already freed ct_ft object. This vulnerability can lead to privilege escalation. Analysis from zdi-disclosures@trendmicro.com: When initializing act_ct, tcf_ct_init() is called, which internally triggers tcf_ct_flow_table_get(). static int tcf_ct_flow_table_get(struct net *net, struct tcf_ct_params *params) { struct zones_ht_key key = { .net = net, .zone = params->zone }; struct tcf_ct_flow_table *ct_ft; int err = -ENOMEM; mutex_lock(&zones_mutex); ct_ft = rhashtable_lookup_fast(&zones_ht, &key, zones_params); // [1] if (ct_ft && refcount_inc_not_zero(&ct_ft->ref)) // [2] goto out_unlock; ... } static __always_inline void *rhashtable_lookup_fast( struct rhashtable *ht, const void *key, const struct rhashtable_params params) { void *obj; rcu_read_lock(); obj = rhashtable_lookup(ht, key, params); rcu_read_unlock(); return obj; } At [1], rhashtable_lookup_fast() looks up and returns the corresponding ct_ft from zones_ht . The lookup is performed within an RCU read critical section through rcu_read_lock() / rcu_read_unlock(), which prevents the object from being freed. However, at the point of function return, rcu_read_unlock() has already been called, and there is nothing preventing ct_ft from being freed before reaching refcount_inc_not_zero(&ct_ft->ref) at [2]. This interval becomes the race window, during which ct_ft can be freed. Free Process: tcf_ct_flow_table_put() is executed through the path tcf_ct_cleanup() call_rcu() tcf_ct_params_free_rcu() tcf_ct_params_free() tcf_ct_flow_table_put(). static void tcf_ct_flow_table_put(struct tcf_ct_flow_table *ct_ft) { if (refcount_dec_and_test(&ct_ft->ref)) { rhashtable_remove_fast(&zones_ht, &ct_ft->node, zones_params); INIT_RCU_WORK(&ct_ft->rwork, tcf_ct_flow_table_cleanup_work); // [3] queue_rcu_work(act_ct_wq, &ct_ft->rwork); } } At [3], tcf_ct_flow_table_cleanup_work() is scheduled as RCU work static void tcf_ct_flow_table_cleanup_work(struct work_struct *work) { struct tcf_ct_flow_table *ct_ft; struct flow_block *block; ct_ft = container_of(to_rcu_work(work), struct tcf_ct_flow_table, rwork); nf_flow_table_free(&ct_ft->nf_ft); block = &ct_ft->nf_ft.flow_block; down_write(&ct_ft->nf_ft.flow_block_lock); WARN_ON(!list_empty(&block->cb_list)); up_write(&ct_ft->nf_ft.flow_block_lock); kfree(ct_ft); // [4] module_put(THIS_MODULE); } tcf_ct_flow_table_cleanup_work() frees ct_ft at [4]. When this function executes between [1] and [2], UAF occurs. This race condition has a very short race window, making it generally difficult to trigger. Therefore, to trigger the vulnerability an msleep(100) was inserted after[1] Fixes: 138470a9b2cc2 ("net/sched: act_ct: fix lockdep splat in tcf_ct_flow_table_get") Reported-by: zdi-disclosures@trendmicro.com Tested-by: Victor Nogueira Signed-off-by: Jamal Hadi Salim Link: https://patch.msgid.link/20260410111627.46611-1-jhs@mojatatu.com Signed-off-by: Jakub Kicinski Signed-off-by: Sasha Levin --- net/sched/act_ct.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff --git a/net/sched/act_ct.c b/net/sched/act_ct.c index 945b64be4c1f1..c82755749211c 100644 --- a/net/sched/act_ct.c +++ b/net/sched/act_ct.c @@ -326,9 +326,13 @@ static int tcf_ct_flow_table_get(struct net *net, struct tcf_ct_params *params) int err = -ENOMEM; mutex_lock(&zones_mutex); - ct_ft = rhashtable_lookup_fast(&zones_ht, &key, zones_params); - if (ct_ft && refcount_inc_not_zero(&ct_ft->ref)) + rcu_read_lock(); + ct_ft = rhashtable_lookup(&zones_ht, &key, zones_params); + if (ct_ft && refcount_inc_not_zero(&ct_ft->ref)) { + rcu_read_unlock(); goto out_unlock; + } + rcu_read_unlock(); ct_ft = kzalloc(sizeof(*ct_ft), GFP_KERNEL); if (!ct_ft) -- 2.53.0