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                "id": "CVE-2024-38663",
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      "affected": [
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          "defaultStatus": "unaffected",
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          "programFiles": [
            "block/blk-cgroup.c"
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        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nblk-cgroup: fix list corruption from resetting io stat\n\nSince commit 3b8cc6298724 (\"blk-cgroup: Optimize blkcg_rstat_flush()\"),\neach iostat instance is added to blkcg percpu list, so blkcg_reset_stats()\ncan\u0027t reset the stat instance by memset(), otherwise the llist may be\ncorrupted.\n\nFix the issue by only resetting the counter part."
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      ],
      "metrics": [
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          "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"
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          "scenarios": [
            {
              "lang": "en",
              "value": "AV:L - The vulnerability is triggered by writing to the cgroup v1 control file `blkio.reset_stats` and by submitting block I/O from the same cgroup, both of which require local access to the machine (cgroupfs write + write(2)/read(2) to a block device or file). There is no network, adjacent-network, or physical path into `blkcg_reset_stats()`.\nAC:L - The attacker controls both sides of the race: they generate I/O inside their own cgroup to populate `blkcg-\u003elhead` via `blk_cgroup_bio_start()` and concurrently write `blkio.reset_stats` in a loop from another thread, and `blkcg_reset_stats()` takes only `blkcg-\u003elock`, which the I/O path never acquires. Once `lqueued` is cleared on a still-linked node, the very next bio deterministically re-adds it and forms a cycle \u2014 no memory layout or timing outside the attacker\u0027s influence is needed, and failed attempts can be retried indefinitely.\nPR:L - `cgroup_kn_set_ugid()` explicitly sets cgroup directories and control files to the uid/gid of their creator, so an unprivileged user or container root with write access to a delegated cgroup v1 blkio subtree (standard in LXC/LXD, Docker/Kubernetes, and systemd `Delegate=` setups) can `mkdir` a child cgroup and own its `blkio.reset_stats` file, then generate I/O and write it. No init-namespace root or capability is required, and the resulting lockless-list corruption is not confined to the attacker\u0027s own cgroup \u2014 it hangs the whole machine.\nUI:N - The attacker performs both the I/O submission and the `blkio.reset_stats` write from their own processes; no victim has to mount, open, or otherwise interact with anything.\nS:U - The corrupted `blkg_iostat_set` lockless lists and the resulting crash/corruption are entirely within the kernel\u0027s own security authority; no VM, hypervisor, or IOMMU boundary is crossed by the bug itself.\nC:H - This is a memory-corruption defect \u2014 `memset()` over live `llist_node` linkage and the `lqueued` membership flag inside per-CPU `blkg_iostat_set` objects \u2014 which desynchronizes the list-membership invariant that the blkg lifetime rules depend on (in the v6.2\u2013v6.4 part of the affected range llist membership held a `percpu_ref` on `blkg-\u003erefcnt`, so lost/duplicated puts corrupt `struct blkcg_gq` lifetime accounting). The same broken invariant in this exact function has since produced a confirmed slab use-after-free in `__blkcg_rstat_flush()`, and dangling/looped links into kmalloc\u0027d blkg and per-CPU stat memory are leverageable for kernel memory disclosure via heap grooming.\nI:H - The corrupted links cause `__blkcg_rstat_flush()` to write unbounded, attacker-influenced counter deltas through the cyclic chain into ancestor blkgs\u0027 `iostat` (`blkcg_iostat_update(parent, ...)`), modifying kernel state belonging to higher-privileged cgroups, and the underlying pointer/refcount corruption of `struct blkcg_gq` is the classic primitive for heap grooming and writes through stale pointers. Per kernel CNA practice, list corruption of this class is treated as exploitable for control-flow-relevant memory modification.\nA:H - The reliable, immediate outcome is a cyclic lockless list that makes `llist_for_each_entry_safe()` in `__blkcg_rstat_flush()` spin forever while holding the global `raw_spinlock_t blkg_stat_lock` with local IRQs disabled \u2014 every other CPU entering rstat flush then spins too, producing a hard lockup and watchdog panic. Additionally, the `memset`-to-`bis-\u003eblkg = blkg` window lets a concurrent flush dereference a NULL `blkg`, and the truncated chains permanently leak blkg references and per-CPU stats."
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      "title": "blk-cgroup: fix list corruption from resetting io stat",
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    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2024-38663",
    "datePublished": "2024-06-24T13:50:51.710Z",
    "dateReserved": "2024-06-21T11:16:40.592Z",
    "dateUpdated": "2026-08-05T11:33:20.039Z",
    "state": "PUBLISHED"
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