CVE-2026-68138 (GCVE-0-2026-68138)
Vulnerability from cvelistv5
Published
2026-08-10 11:59
Modified
2026-08-23 12:45
Severity ?
7.8 (High) - CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Summary
In the Linux kernel, the following vulnerability has been resolved: net/sched: serialize qdisc_rtab_list against concurrent get/put qdisc_get_rtab() and qdisc_put_rtab() mutate the process-global singly linked list qdisc_rtab_list and a plain non-atomic 'int refcnt' with no lock. This was only safe because every caller historically held the RTNL mutex, which serialized all rate-table lookups, inserts and frees. That invariant no longer holds. cls_flower sets TCF_PROTO_OPS_DOIT_UNLOCKED, so tc_new_tfilter() keeps rtnl_held == false for it and sets TCA_ACT_FLAGS_NO_RTNL. That flag propagates through tcf_exts_validate_ex() -> tcf_action_init() -> tcf_action_init_1() -> tcf_police_init(), which calls qdisc_get_rtab()/qdisc_put_rtab() with the RTNL mutex NOT held. Two RTM_NEWTFILTER requests on different CPUs, each adding a flower filter with a police action carrying the same rate, then race on qdisc_rtab_list and on the non-atomic refcnt, leading to a use-after-free / double-free of the kmalloc-2k struct qdisc_rate_table. qdisc_rtab_list is a single global (not per-netns), so the corrupted object is shared system-wide. BUG: KASAN: slab-use-after-free in qdisc_put_rtab+0x12f/0x160 qdisc_put_rtab+0x12f/0x160 tcf_police_init+0xda9/0x1590 tcf_action_init_1+0x460/0x6b0 tcf_action_init+0x439/0xa40 tcf_exts_validate_ex+0x42d/0x550 fl_change+0xddd/0x7da0 tc_new_tfilter+0xaa7/0x2420 rtnetlink_rcv_msg+0x95e/0xe90 which belongs to the cache kmalloc-2k of size 2048 Protect qdisc_rtab_list and the refcount with a dedicated spinlock. The (sleeping, GFP_KERNEL) allocation in qdisc_get_rtab() is performed before taking the lock; if a concurrent inserter added an identical table in the meantime the freshly allocated one is freed under the lock, so no duplicate is leaked. qdisc_put_rtab() now decrements the refcount and unlinks under the same lock.
References
Impacted products
Vendor Product Version
Linux Linux Version: 470502de5bdb1ed0def643a4458593a40b8f6b66
Version: 470502de5bdb1ed0def643a4458593a40b8f6b66
Version: 470502de5bdb1ed0def643a4458593a40b8f6b66
Version: 470502de5bdb1ed0def643a4458593a40b8f6b66
Version: 470502de5bdb1ed0def643a4458593a40b8f6b66
Version: 470502de5bdb1ed0def643a4458593a40b8f6b66
Version: 470502de5bdb1ed0def643a4458593a40b8f6b66
Version: 470502de5bdb1ed0def643a4458593a40b8f6b66
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{
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          "programFiles": [
            "net/sched/sch_api.c"
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      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet/sched: serialize qdisc_rtab_list against concurrent get/put\n\nqdisc_get_rtab() and qdisc_put_rtab() mutate the process-global singly\nlinked list qdisc_rtab_list and a plain non-atomic \u0027int refcnt\u0027 with no\nlock. This was only safe because every caller historically held the RTNL\nmutex, which serialized all rate-table lookups, inserts and frees.\n\nThat invariant no longer holds. cls_flower sets\nTCF_PROTO_OPS_DOIT_UNLOCKED, so tc_new_tfilter() keeps rtnl_held == false\nfor it and sets TCA_ACT_FLAGS_NO_RTNL. That flag propagates through\ntcf_exts_validate_ex() -\u003e tcf_action_init() -\u003e tcf_action_init_1() -\u003e\ntcf_police_init(), which calls qdisc_get_rtab()/qdisc_put_rtab() with the\nRTNL mutex NOT held. Two RTM_NEWTFILTER requests on different CPUs, each\nadding a flower filter with a police action carrying the same rate, then\nrace on qdisc_rtab_list and on the non-atomic refcnt, leading to a\nuse-after-free / double-free of the kmalloc-2k struct qdisc_rate_table.\nqdisc_rtab_list is a single global (not per-netns), so the corrupted\nobject is shared system-wide.\n\n  BUG: KASAN: slab-use-after-free in qdisc_put_rtab+0x12f/0x160\n   qdisc_put_rtab+0x12f/0x160\n   tcf_police_init+0xda9/0x1590\n   tcf_action_init_1+0x460/0x6b0\n   tcf_action_init+0x439/0xa40\n   tcf_exts_validate_ex+0x42d/0x550\n   fl_change+0xddd/0x7da0\n   tc_new_tfilter+0xaa7/0x2420\n   rtnetlink_rcv_msg+0x95e/0xe90\n  which belongs to the cache kmalloc-2k of size 2048\n\nProtect qdisc_rtab_list and the refcount with a dedicated spinlock. The\n(sleeping, GFP_KERNEL) allocation in qdisc_get_rtab() is performed before\ntaking the lock; if a concurrent inserter added an identical table in the\nmeantime the freshly allocated one is freed under the lock, so no\nduplicate is leaked. qdisc_put_rtab() now decrements the refcount and\nunlinks under the same lock."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 7.8,
            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
            "version": "3.1"
          },
          "scenarios": [
            {
              "lang": "en",
              "value": "AV:L - The bug is reached only via local RTM_NEWTFILTER rtnetlink messages (tc flower filter with police action) through rtnetlink_rcv_msg\u2192tc_new_tfilter\u2192fl_change\u2192tcf_police_init\u2192qdisc_get_rtab/qdisc_put_rtab; no remote packet or network protocol path exists.\nAC:L - cls_flower is TCF_PROTO_OPS_DOIT_UNLOCKED, so concurrent RTM_NEWTFILTER requests run without RTNL; the attacker controls both racing threads/CPUs and can repeatedly install flower filters with identical police rate tables to deterministically hit the global qdisc_rtab_list/refcnt race.\nPR:L - Non-GET rtnetlink handlers require netlink_net_capable(CAP_NET_ADMIN); this is namespace-scoped, so an unprivileged local user obtains CAP_NET_ADMIN via user namespaces (unshare -Urn), sets up clsact/ingress, and installs flower+police rules without init-namespace root.\nUI:N - Exploitation is fully self-contained: the attacker issues the concurrent tc/netlink commands from its own processes and needs no victim to mount filesystems, click links, or perform any other interactive action.\nS:U - Impact is heap corruption and UAF/double-free in kernel kmalloc-2k slabs within the same kernel security authority; although qdisc_rtab_list is global across netns, this is standard kernel memory corruption/privilege escalation, not a VM, IOMMU, or sandbox boundary escape.\nC:H - Concurrent non-atomic refcnt and list updates cause slab use-after-free/double-free of struct qdisc_rate_table (KASAN-confirmed in qdisc_put_rtab); freed 2KB objects are attacker-influenceable via kmalloc timing and are classically weaponizable for arbitrary kernel memory disclosure.\nI:H - The race corrupts a process-global singly linked list and can double-free a kmalloc-2k qdisc_rate_table, yielding classic heap metadata/object corruption primitives that can be developed into arbitrary kernel writes and local privilege escalation/code execution.\nA:H - Demonstrated KASAN slab-use-after-free in qdisc_put_rtab on the error/teardown path, and concurrent double-free of the same rate table can panic the kernel; the trigger is repeatable at will with concurrent netlink requests and causes task death or system-wide instability."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-23T12:45:55.796Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/1b050d09dd1a0ddae83bf012cf4956b7a960235f"
        },
        {
          "url": "https://git.kernel.org/stable/c/6e0241f6cbb149d926ee8efee2c734fea71452cf"
        },
        {
          "url": "https://git.kernel.org/stable/c/f93c89392bd3b180b5b7abc6fdae8e3dd667a313"
        },
        {
          "url": "https://git.kernel.org/stable/c/4131dd0b6f67acddd616ed7c244e1d3eedd46e7b"
        },
        {
          "url": "https://git.kernel.org/stable/c/d981098b76756ed71666a27518eeb69883657c43"
        },
        {
          "url": "https://git.kernel.org/stable/c/8ddc2eb0d2da9c83f54f1e5720525b461b8480c4"
        },
        {
          "url": "https://git.kernel.org/stable/c/fb29e1b41052488ee3f2d115d4a870497ebd7f7d"
        },
        {
          "url": "https://git.kernel.org/stable/c/f43ee0c0730d6191629b5ee1ceae27b1ebfdc047"
        }
      ],
      "title": "net/sched: serialize qdisc_rtab_list against concurrent get/put",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-68138",
    "datePublished": "2026-08-10T11:59:01.744Z",
    "dateReserved": "2026-07-30T09:28:09.370Z",
    "dateUpdated": "2026-08-23T12:45:55.796Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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