GHSA-X4GP-7H95-W6VP
Vulnerability from github – Published: 2026-08-22 18:30 – Updated: 2026-08-23 15:33In 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.
{
"affected": [],
"aliases": [
"CVE-2026-74620"
],
"database_specific": {
"cwe_ids": [],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-08-22T16:16:34Z",
"severity": null
},
"details": "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.",
"id": "GHSA-x4gp-7h95-w6vp",
"modified": "2026-08-23T15:33:03Z",
"published": "2026-08-22T18:30:27Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-74620"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/2e8df8c9190335475a3b64a159d3efd8cdd1cb73"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/5344e01179baa37547ab29fd7b8614f83faa190c"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/5f038affdacaffedf6a85a06cf59ec0a852d36a7"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/6bcb8839aa2d686964a4154650afc4db91e1c514"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/725efc2ab4a40affc4e285a2dc4896d103948a6c"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/883b56ae58fe657d8497806c7059646e9ba6dbd0"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/92f00f1d4d204a428b38e26fce3baee144b6955d"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/efa58aeb6a99028b1fbc3ab2f31ba3a881211ad4"
}
],
"schema_version": "1.4.0",
"severity": []
}
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