Affected: Linux

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_re…