CVE-2026-46319 (GCVE-0-2026-46319)
Vulnerability from cvelistv5
Published
2026-06-09 12:11
Modified
2026-06-09 12:11
Severity ?
Summary
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]
References
Impacted products
Vendor Product Version
Linux Linux Version: 138470a9b2cc2e26e6018300394afc3858a54e6a
Version: 138470a9b2cc2e26e6018300394afc3858a54e6a
Version: 138470a9b2cc2e26e6018300394afc3858a54e6a
Version: 138470a9b2cc2e26e6018300394afc3858a54e6a
Version: 138470a9b2cc2e26e6018300394afc3858a54e6a
Version: 138470a9b2cc2e26e6018300394afc3858a54e6a
Version: 138470a9b2cc2e26e6018300394afc3858a54e6a
Version: 138470a9b2cc2e26e6018300394afc3858a54e6a
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{
  "containers": {
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          "product": "Linux",
          "programFiles": [
            "net/sched/act_ct.c"
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          "vendor": "Linux",
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            },
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              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.1-rc1",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
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              ],
              "negate": false,
              "operator": "OR"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "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]"
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-06-09T12:11:12.128Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/ece578ca61e572df96cfc80456357ebfae0b4b9e"
        },
        {
          "url": "https://git.kernel.org/stable/c/a2e0c045c87aa252eb61412e67dd91f2c2b19f81"
        },
        {
          "url": "https://git.kernel.org/stable/c/67c9ecc9f2575273ed1323e312881fc98ac83d6d"
        },
        {
          "url": "https://git.kernel.org/stable/c/f23424a0ddadb494d4bd57056a7ca703312d3a7b"
        },
        {
          "url": "https://git.kernel.org/stable/c/17dfb67cb399b660105d9a8c6100851c0d0cdc70"
        },
        {
          "url": "https://git.kernel.org/stable/c/4c727c6967a41b37efe0f26332ca9ec5b74785a3"
        },
        {
          "url": "https://git.kernel.org/stable/c/3e20e1b3058e0b94638e7b931c138e840e266724"
        },
        {
          "url": "https://git.kernel.org/stable/c/f462dca0c8415bf0058d0ffa476354c4476d0f09"
        }
      ],
      "title": "net/sched: act_ct: Only release RCU read lock after ct_ft",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-46319",
    "datePublished": "2026-06-09T12:11:12.128Z",
    "dateReserved": "2026-05-13T15:03:33.112Z",
    "dateUpdated": "2026-06-09T12:11:12.128Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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