GHSA-Q9HW-VHJ5-HW57

Vulnerability from github – Published: 2026-06-09 15:32 – Updated: 2026-06-14 06:30
VLAI
Details

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]

Severity
7.8 (High)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Show details on source website
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{
  "affected": [],
  "aliases": [
    "CVE-2026-46319"
  ],
  "database_specific": {
    "cwe_ids": [],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-06-09T13:16:37Z",
    "severity": "HIGH"
  },
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet/sched: act_ct: Only release RCU read lock after ct_ft\n\nWhen looking up a flow table in act_ct in tcf_ct_flow_table_get(),\nrhashtable_lookup_fast() internally opens and closes an RCU read critical\nsection before returning ct_ft.\nThe tcf_ct_flow_table_cleanup_work() can complete before refcount_inc_not_zero()\nis invoked on the returned ct_ft resulting in a UAF on the already freed ct_ft\nobject. This vulnerability can lead to privilege escalation.\n\nAnalysis from zdi-disclosures@trendmicro.com:\nWhen initializing act_ct, tcf_ct_init() is called, which internally triggers\ntcf_ct_flow_table_get().\n\nstatic int tcf_ct_flow_table_get(struct net *net, struct tcf_ct_params *params)\n\n{\n                struct zones_ht_key key = { .net = net, .zone = params-\u003ezone };\n                struct tcf_ct_flow_table *ct_ft;\n                int err = -ENOMEM;\n\n                mutex_lock(\u0026zones_mutex);\n                ct_ft = rhashtable_lookup_fast(\u0026zones_ht, \u0026key, zones_params); // [1]\n                if (ct_ft \u0026\u0026 refcount_inc_not_zero(\u0026ct_ft-\u003eref)) // [2]\n                                goto out_unlock;\n                ...\n}\n\nstatic __always_inline void *rhashtable_lookup_fast(\n                struct rhashtable *ht, const void *key,\n                const struct rhashtable_params params)\n{\n                void *obj;\n\n                rcu_read_lock();\n                obj = rhashtable_lookup(ht, key, params);\n                rcu_read_unlock();\n\n                return obj;\n}\n\nAt [1], rhashtable_lookup_fast() looks up and returns the corresponding ct_ft\nfrom zones_ht . The lookup is performed within an RCU read critical section\nthrough rcu_read_lock() / rcu_read_unlock(), which prevents the object from\nbeing freed. However, at the point of function return, rcu_read_unlock() has\nalready been called, and there is nothing preventing ct_ft from being freed\nbefore reaching refcount_inc_not_zero(\u0026ct_ft-\u003eref) at [2]. This interval becomes\nthe race window, during which ct_ft can be freed.\n\nFree Process:\n\ntcf_ct_flow_table_put() is executed through the path tcf_ct_cleanup() call_rcu()\ntcf_ct_params_free_rcu() tcf_ct_params_free() tcf_ct_flow_table_put().\n\nstatic void tcf_ct_flow_table_put(struct tcf_ct_flow_table *ct_ft)\n{\n                if (refcount_dec_and_test(\u0026ct_ft-\u003eref)) {\n                                rhashtable_remove_fast(\u0026zones_ht, \u0026ct_ft-\u003enode, zones_params);\n                                INIT_RCU_WORK(\u0026ct_ft-\u003erwork, tcf_ct_flow_table_cleanup_work); // [3]\n                                queue_rcu_work(act_ct_wq, \u0026ct_ft-\u003erwork);\n                }\n}\n\nAt [3], tcf_ct_flow_table_cleanup_work() is scheduled as RCU work\n\nstatic void tcf_ct_flow_table_cleanup_work(struct work_struct *work)\n\n{\n                struct tcf_ct_flow_table *ct_ft;\n                struct flow_block *block;\n\n                ct_ft = container_of(to_rcu_work(work), struct tcf_ct_flow_table,\n                                                                rwork);\n                nf_flow_table_free(\u0026ct_ft-\u003enf_ft);\n                block = \u0026ct_ft-\u003enf_ft.flow_block;\n                down_write(\u0026ct_ft-\u003enf_ft.flow_block_lock);\n                WARN_ON(!list_empty(\u0026block-\u003ecb_list));\n                up_write(\u0026ct_ft-\u003enf_ft.flow_block_lock);\n                kfree(ct_ft); // [4]\n\n                module_put(THIS_MODULE);\n}\n\ntcf_ct_flow_table_cleanup_work() frees ct_ft at [4]. When this function executes\nbetween [1] and [2], UAF occurs.\n\nThis race condition has a very short race window, making it generally\ndifficult to trigger. Therefore, to trigger the vulnerability an msleep(100) was\ninserted after[1]",
  "id": "GHSA-q9hw-vhj5-hw57",
  "modified": "2026-06-14T06:30:24Z",
  "published": "2026-06-09T15:32:18Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-46319"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/17dfb67cb399b660105d9a8c6100851c0d0cdc70"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/3e20e1b3058e0b94638e7b931c138e840e266724"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/4c727c6967a41b37efe0f26332ca9ec5b74785a3"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/67c9ecc9f2575273ed1323e312881fc98ac83d6d"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/a2e0c045c87aa252eb61412e67dd91f2c2b19f81"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/ece578ca61e572df96cfc80456357ebfae0b4b9e"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/f23424a0ddadb494d4bd57056a7ca703312d3a7b"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/f462dca0c8415bf0058d0ffa476354c4476d0f09"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
      "type": "CVSS_V3"
    }
  ]
}


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