CVE-2026-90326 (GCVE-0-2026-90326)
Vulnerability from cvelistv5
Published
2026-09-17 16:08
Modified
2026-10-21 12:51
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: blk-cgroup: fix race between policy activation and blkg destruction When switching an IO scheduler on a block device, blkcg_activate_policy() allocates blkg_policy_data (pd) for all blkgs attached to the queue. However, blkcg_activate_policy() may race with concurrent blkcg deletion, leading to use-after-free and memory leak issues. The use-after-free occurs in the following race: T1 (blkcg_activate_policy): - Successfully allocates pd for blkg1 (loop0->queue, blkcgA) - Fails to allocate pd for blkg2 (loop0->queue, blkcgB) - Enters the enomem rollback path to release blkg1 resources T2 (blkcg deletion): - blkcgA is deleted concurrently - blkg1 is freed via blkg_free_workfn() - blkg1->pd is freed T1 (continued): - Rollback path accesses blkg1->pd->online after pd is freed - Triggers use-after-free In addition, blkg_free_workfn() frees pd before removing the blkg from q->blkg_list. This allows blkcg_activate_policy() to allocate a new pd for a blkg that is being destroyed, leaving the newly allocated pd unreachable when the blkg is finally freed. Fix these races by extending blkcg_mutex coverage to serialize blkcg_activate_policy() rollback and blkg destruction, ensuring pd lifecycle is synchronized with blkg list visibility.
References
Impacted products
Vendor Product Version
Linux Linux Version: 81c1188905f88b77743d1fdeeedfc8cb7b67787d
Version: bfe46d2efe46c5c952f982e2ca94fe2ec5e58e2a
Version: f1c006f1c6850c14040f8337753a63119bba39b9
Version: f1c006f1c6850c14040f8337753a63119bba39b9
Version: f1c006f1c6850c14040f8337753a63119bba39b9
Version: f1c006f1c6850c14040f8337753a63119bba39b9
Version: f1c006f1c6850c14040f8337753a63119bba39b9
Version: 6.1.16   ≤
Version: 6.2.3   ≤
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{
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        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "block/blk-cgroup.c"
          ],
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      "cpeApplicability": [
        {
          "nodes": [
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              "negate": false,
              "operator": "OR"
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          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nblk-cgroup: fix race between policy activation and blkg destruction\n\nWhen switching an IO scheduler on a block device, blkcg_activate_policy()\nallocates blkg_policy_data (pd) for all blkgs attached to the queue.\nHowever, blkcg_activate_policy() may race with concurrent blkcg deletion,\nleading to use-after-free and memory leak issues.\n\nThe use-after-free occurs in the following race:\n\nT1 (blkcg_activate_policy):\n  - Successfully allocates pd for blkg1 (loop0-\u003equeue, blkcgA)\n  - Fails to allocate pd for blkg2 (loop0-\u003equeue, blkcgB)\n  - Enters the enomem rollback path to release blkg1 resources\n\nT2 (blkcg deletion):\n  - blkcgA is deleted concurrently\n  - blkg1 is freed via blkg_free_workfn()\n  - blkg1-\u003epd is freed\n\nT1 (continued):\n  - Rollback path accesses blkg1-\u003epd-\u003eonline after pd is freed\n  - Triggers use-after-free\n\nIn addition, blkg_free_workfn() frees pd before removing the blkg from\nq-\u003eblkg_list. This allows blkcg_activate_policy() to allocate a new pd\nfor a blkg that is being destroyed, leaving the newly allocated pd\nunreachable when the blkg is finally freed.\n\nFix these races by extending blkcg_mutex coverage to serialize\nblkcg_activate_policy() rollback and blkg destruction, ensuring pd\nlifecycle is synchronized with blkg list visibility."
        }
      ],
      "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 triggering operations are local cgroupfs writes: tg_set_limit() (io.max) or iolatency_set_limit() (io.latency) call blk_throtl_init()/blk_iolatency_init() then blkcg_activate_policy(), while cgroup_rmdir() runs blkcg_css_offline() into blkg_free_workfn(); elv_iosched_store() is an alternate local sysfs path. No remote protocol carries the race inputs.\nAC:L - The attacker drives both sides: one thread writes io.max/io.latency so blkcg_activate_policy() attaches pd without q-\u003eblkcg_mutex, while another rmdirs sibling blkcgs so blkg_free_workfn() calls pd_free_fn() on the same blkg-\u003epd[] before list_del. That interleaving does not depend on GFP_KERNEL failure; the documented enomem rollback UAF on pd-\u003eonline is an extra window the attacker can retry.\nPR:L - tg_set_limit() and iolatency_set_limit() have no capable() check; io.max/io.latency are CFTYPE_NOT_ON_ROOT S_IWUSR files, and blkg_conf_open_bdev() uses blkdev_get_no_open() with no device permission check. A delegated cgroup-v2 subtree owner (typical systemd user slice or rootless container) can write those files and rmdir child cgroups; scheduler sysfs is a stricter alternate path.\nUI:N - The attacker writes io.max/io.latency in cgroups they own and rmdirs those cgroups themselves; no other user must mount a device, open a file, or otherwise participate.\nS:U - The UAF corrupts kernel blkg_policy_data (throtl_grp/iolatency_grp) in the host io controller; impact stays in the kernel\u0027s authority and does not cross a VM, IOMMU, or other security boundary.\nC:H - blkg_free_workfn() frees blkg-\u003epd[] while the object remains on q-\u003eblkg_list, so blkcg_activate_policy()\u0027s enomem path reads pd-\u003eonline and pd_offline_fn() (throtl_pd_offline()/tg_flush_bios()) walks the freed throtl_grp; spraying the slab reclaims that object for an arbitrary kernel read.\nI:H - The same freed pd is written (pd-\u003eonline = false) and passed to pol-\u003epd_free_fn() again (throtl_pd_free() does timer_delete_sync() and call_rcu()), a double-free of throtl_grp/iolatency_grp that yields a kernel write/control-flow primitive.\nA:H - Use-after-free and double-free of blkg_policy_data in blkcg_activate_policy() versus blkg_free_workfn() oops/panic the kernel even when not turned into a full memory primitive."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-10-21T12:51:00.266Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/b5dae1cd0d8368b4338430ff93403df67f0b8bcc"
        },
        {
          "url": "https://git.kernel.org/stable/c/083b58373463a6e5ee60ecb135269348f68ad7df"
        },
        {
          "url": "https://git.kernel.org/stable/c/17c18a0df70c2b89ff7fcd74622f1540e98d00fd"
        },
        {
          "url": "https://git.kernel.org/stable/c/91062e3a9ed251726df4e20ff9a1113f1c8ded59"
        },
        {
          "url": "https://git.kernel.org/stable/c/ac34e655dffa74349d885a43d098115336f53842"
        },
        {
          "url": "https://git.kernel.org/stable/c/2cf9f50a38c1839e549a08e22aa35e8d69e2c8fd"
        },
        {
          "url": "https://git.kernel.org/stable/c/5313d4d41739b0cb63000747c97bb1217ac45f3e"
        }
      ],
      "title": "blk-cgroup: fix race between policy activation and blkg destruction",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-90326",
    "datePublished": "2026-09-17T16:08:41.374Z",
    "dateReserved": "2026-09-11T19:38:34.802Z",
    "dateUpdated": "2026-10-21T12:51:00.266Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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