CVE-2026-74620 (GCVE-0-2026-74620)
Vulnerability from cvelistv5
Published
2026-08-22 15:32
Modified
2026-08-23 12:47
Severity ?
Summary
In the Linux kernel, the following vulnerability has been resolved: net/sched: act_gact, act_police: range check the fallback control action tcf_action_check_ctrlact() range checks the primary control action: if (!opcode) ret = action > TC_ACT_VALUE_MAX ? -EINVAL : 0; TC_ACT_VALUE_MAX is TC_ACT_TRAP, so kernel-internal verdicts above it cannot be set that way. But act_gact and act_police each carry a second, independent control action supplied by user space that never reaches that helper - TCA_GACT_PROB.paction and TCA_POLICE_RESULT. Both only reject TC_ACT_GOTO_CHAIN, so any other value is stored verbatim and returned verbatim from the action. In particular user space can store TC_ACT_CONSUMED, which is TC_ACT_VALUE_MAX + 1 and is deliberately not part of the UAPI value range. That verdict tells every caller the action took ownership of the skb, so nobody frees it: sch_handle_ingress(), sch_handle_egress() and tcf_qevent_handle() all deliberately skip the free for it. The result is one leaked sk_buff plus its data buffer per packet traversing the filter, unbounded, for all traffic on the chain including kernel-generated packets. Both are trivially deterministic. act_gact clamps tcfg_pval to >= 1, so with pval = 1 gact_determ() returns the fallback for every packet. act_police has no mandatory rate, so rate = 0 leaves tcfp_mtu = ~0 and tcf_police_mtu_check() always passes. TC_ACT_CONSUMED was added by commit 720f22fed81b ("net: sched: refactor reinsert action"), after both goto-chain guards were written: commit 9469f375ab09 ("net/sched: act_gact: disallow 'goto chain' on fallback control action") and commit c08f5ed5d625 ("net/sched: act_police: disallow 'goto chain' on fallback control action"). Neither guard was widened when the new verdict appeared. Factor the existing range test out of tcf_action_check_ctrlact() as tcf_action_valid() and apply it to both fallbacks. The helper cannot call tcf_action_check_ctrlact() directly because that also allocates a goto_chain, which is exactly what these two sites must not do. Reproduced on v7.2-rc6: kmemleak reports one leaked 232-byte skbuff_head_cache object plus its 704-byte data buffer per packet. With this patch both configurations are rejected with -EINVAL and kmemleak reports none.
References
Impacted products
Vendor Product Version
Linux Linux Version: 720f22fed81bc6fd1765db7014651b6718887bea
Version: 720f22fed81bc6fd1765db7014651b6718887bea
Version: 720f22fed81bc6fd1765db7014651b6718887bea
Version: 720f22fed81bc6fd1765db7014651b6718887bea
Version: 720f22fed81bc6fd1765db7014651b6718887bea
Version: 720f22fed81bc6fd1765db7014651b6718887bea
Version: 720f22fed81bc6fd1765db7014651b6718887bea
Version: 720f22fed81bc6fd1765db7014651b6718887bea
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{
  "containers": {
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          "product": "Linux",
          "programFiles": [
            "include/net/act_api.h",
            "net/sched/act_gact.c",
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      "cpeApplicability": [
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      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet/sched: act_gact, act_police: range check the fallback control action\n\ntcf_action_check_ctrlact() range checks the primary control action:\n\n\tif (!opcode)\n\t\tret = action \u003e TC_ACT_VALUE_MAX ? -EINVAL : 0;\n\nTC_ACT_VALUE_MAX is TC_ACT_TRAP, so kernel-internal verdicts above it\ncannot be set that way. But act_gact and act_police each carry a second,\nindependent control action supplied by user space that never reaches that\nhelper - TCA_GACT_PROB.paction and TCA_POLICE_RESULT. Both only reject\nTC_ACT_GOTO_CHAIN, so any other value is stored verbatim and returned\nverbatim from the action.\n\nIn particular user space can store TC_ACT_CONSUMED, which is\nTC_ACT_VALUE_MAX + 1 and is deliberately not part of the UAPI value\nrange. That verdict tells every caller the action took ownership of the\nskb, so nobody frees it: sch_handle_ingress(), sch_handle_egress() and\ntcf_qevent_handle() all deliberately skip the free for it. The result is\none leaked sk_buff plus its data buffer per packet traversing the filter,\nunbounded, for all traffic on the chain including kernel-generated\npackets.\n\nBoth are trivially deterministic. act_gact clamps tcfg_pval to \u003e= 1, so\nwith pval = 1 gact_determ() returns the fallback for every packet.\nact_police has no mandatory rate, so rate = 0 leaves tcfp_mtu = ~0 and\ntcf_police_mtu_check() always passes.\n\nTC_ACT_CONSUMED was added by commit 720f22fed81b (\"net: sched: refactor\nreinsert action\"), after both goto-chain guards were written:\ncommit 9469f375ab09 (\"net/sched: act_gact: disallow \u0027goto chain\u0027 on\nfallback control action\") and\ncommit c08f5ed5d625 (\"net/sched: act_police: disallow \u0027goto chain\u0027 on\nfallback control action\"). Neither guard was widened when the new\nverdict appeared.\n\nFactor the existing range test out of tcf_action_check_ctrlact() as\ntcf_action_valid() and apply it to both fallbacks. The helper cannot call\ntcf_action_check_ctrlact() directly because that also allocates a\ngoto_chain, which is exactly what these two sites must not do.\n\nReproduced on v7.2-rc6: kmemleak reports one leaked 232-byte\nskbuff_head_cache object plus its 704-byte data buffer per packet. With\nthis patch both configurations are rejected with -EINVAL and kmemleak\nreports none."
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-23T12:47:46.379Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/5f038affdacaffedf6a85a06cf59ec0a852d36a7"
        },
        {
          "url": "https://git.kernel.org/stable/c/efa58aeb6a99028b1fbc3ab2f31ba3a881211ad4"
        },
        {
          "url": "https://git.kernel.org/stable/c/725efc2ab4a40affc4e285a2dc4896d103948a6c"
        },
        {
          "url": "https://git.kernel.org/stable/c/6bcb8839aa2d686964a4154650afc4db91e1c514"
        },
        {
          "url": "https://git.kernel.org/stable/c/5344e01179baa37547ab29fd7b8614f83faa190c"
        },
        {
          "url": "https://git.kernel.org/stable/c/92f00f1d4d204a428b38e26fce3baee144b6955d"
        },
        {
          "url": "https://git.kernel.org/stable/c/2e8df8c9190335475a3b64a159d3efd8cdd1cb73"
        },
        {
          "url": "https://git.kernel.org/stable/c/883b56ae58fe657d8497806c7059646e9ba6dbd0"
        }
      ],
      "title": "net/sched: act_gact, act_police: range check the fallback control action",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-74620",
    "datePublished": "2026-08-22T15:32:04.254Z",
    "dateReserved": "2026-08-15T05:44:03.921Z",
    "dateUpdated": "2026-08-23T12:47:46.379Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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