{
  "schema_version": "1.6.1",
  "id": "RPI-CVE-2024-56672",
  "modified": "2026-10-09T11:39:44Z",
  "upstream": [
    "CVE-2024-56672"
  ],
  "published": "2024-12-27T15:08:24Z",
  "summary": "blk-cgroup: Fix UAF in blkcg_unpin_online()",
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nblk-cgroup: Fix UAF in blkcg_unpin_online()\n\nblkcg_unpin_online() walks up the blkcg hierarchy putting the online pin. To\nwalk up, it uses blkcg_parent(blkcg) but it was calling that after\nblkcg_destroy_blkgs(blkcg) which could free the blkcg, leading to the\nfollowing UAF:\n\n  ==================================================================\n  BUG: KASAN: slab-use-after-free in blkcg_unpin_online+0x15a/0x270\n  Read of size 8 at addr ffff8881057678c0 by task kworker/9:1/117\n\n  CPU: 9 UID: 0 PID: 117 Comm: kworker/9:1 Not tainted 6.13.0-rc1-work-00182-gb8f52214c61a-dirty #48\n  Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS unknown 02/02/2022\n  Workqueue: cgwb_release cgwb_release_workfn\n  Call Trace:\n   <TASK>\n   dump_stack_lvl+0x27/0x80\n   print_report+0x151/0x710\n   kasan_report+0xc0/0x100\n   blkcg_unpin_online+0x15a/0x270\n   cgwb_release_workfn+0x194/0x480\n   process_scheduled_works+0x71b/0xe20\n   worker_thread+0x82a/0xbd0\n   kthread+0x242/0x2c0\n   ret_from_fork+0x33/0x70\n   ret_from_fork_asm+0x1a/0x30\n   </TASK>\n  ...\n  Freed by task 1944:\n   kasan_save_track+0x2b/0x70\n   kasan_save_free_info+0x3c/0x50\n   __kasan_slab_free+0x33/0x50\n   kfree+0x10c/0x330\n   css_free_rwork_fn+0xe6/0xb30\n   process_scheduled_works+0x71b/0xe20\n   worker_thread+0x82a/0xbd0\n   kthread+0x242/0x2c0\n   ret_from_fork+0x33/0x70\n   ret_from_fork_asm+0x1a/0x30\n\nNote that the UAF is not easy to trigger as the free path is indirected\nbehind a couple RCU grace periods and a work item execution. I could only\ntrigger it with artifical msleep() injected in blkcg_unpin_online().\n\nFix it by reading the parent pointer before destroying the blkcg's blkg's.",
  "severity": [
    {
      "type": "CVSS_V3",
      "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H"
    }
  ],
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  "references": [
    {
      "type": "ADVISORY",
      "url": "https://www.cve.org/CVERecord?id=CVE-2024-56672"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/83f5a87ee8caa76a917f59912a74d6811f773c67"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/8a07350fe070017a887433f4d6909433955be5f1"
    },
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      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/64afc6fe24c9896c0153e5a199bcea241ecb0d5c"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/5baa28569c924d9a90d036c2aaab79f791fedaf8"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/29d1e06560f0f6179062ac638b4064deb637d1ad"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/86e6ca55b83c575ab0f2e105cf08f98e58d3d7af"
    }
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  "database_specific": {
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    "upstream_modified": "2026-08-05T11:52:36Z",
    "severity": {
      "source": "kernel CNA",
      "cvss_v3_score": 7.8,
      "cvss_v3_severity": "High",
      "scenario": "AV:L - The bug is reached only through local operations \u2014 creating/enabling an `io` cgroup, dirtying pages to instantiate a cgroup writeback structure, and rmdir'ing the cgroup. No network-facing code path reaches `blkcg_unpin_online()`.\nAC:L - The attacker drives both sides: the cgwb release that reaches the stale read and the css free chain are both initiated by its own cgroup teardown, and the window is widened at will via `blkcg_destroy_blkgs()`'s `cond_resched()` loop (blkg count, CPU load) while the create/write/rmdir cycle can be repeated indefinitely until the race lands.\nPR:L - An unprivileged user needs only write access to a delegated cgroup v2 subtree with the io controller enabled \u2014 standard under systemd user delegation, container runtimes, and unprivileged podman \u2014 plus ordinary buffered writes; no capability check guards the path.\nUI:N - The attacker performs every step itself \u2014 cgroup creation, file writes, and cgroup removal \u2014 with no victim action required.\nS:U - The corruption occurs in kernel slab memory and impacts the same kernel security authority; no VM, IOMMU, or hypervisor boundary is crossed.\nC:H - `struct blkcg` is allocated from a general kmalloc cache, so the freed object can be sprayed with attacker-controlled data; the stale `css.parent` read produces a controlled pointer that is subsequently dereferenced, giving a path to disclose arbitrary kernel memory.\nI:H - The UAF-derived pointer is fed straight into `refcount_dec_and_test(&blkcg->online_pin)` \u2014 an arbitrary decrement \u2014 and into `blkcg_destroy_blkgs()`, which performs hlist unlink writes on the bogus object, yielding write primitives suitable for control-flow hijack and privilege escalation.\nA:H - Even unweaponized, the slab-use-after-free reliably corrupts memory and oopses/panics the kernel, as demonstrated by the reported KASAN splat in a cgwb_release kworker."
    }
  }
}