Wind River Support Network

Description

In the Linux kernel, the following vulnerability has been resolved:  net/sched: act_ct: Only release RCU read lock after ct_ft  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]