{
  "schema_version": "1.6.1",
  "id": "RPI-CVE-2024-56759",
  "modified": "2026-10-09T11:39:44Z",
  "upstream": [
    "CVE-2024-56759"
  ],
  "published": "2025-01-06T16:21:18Z",
  "summary": "btrfs: fix use-after-free when COWing tree bock and tracing is enabled",
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nbtrfs: fix use-after-free when COWing tree bock and tracing is enabled\n\nWhen a COWing a tree block, at btrfs_cow_block(), and we have the\ntracepoint trace_btrfs_cow_block() enabled and preemption is also enabled\n(CONFIG_PREEMPT=y), we can trigger a use-after-free in the COWed extent\nbuffer while inside the tracepoint code. This is because in some paths\nthat call btrfs_cow_block(), such as btrfs_search_slot(), we are holding\nthe last reference on the extent buffer @buf so btrfs_force_cow_block()\ndrops the last reference on the @buf extent buffer when it calls\nfree_extent_buffer_stale(buf), which schedules the release of the extent\nbuffer with RCU. This means that if we are on a kernel with preemption,\nthe current task may be preempted before calling trace_btrfs_cow_block()\nand the extent buffer already released by the time trace_btrfs_cow_block()\nis called, resulting in a use-after-free.\n\nFix this by moving the trace_btrfs_cow_block() from btrfs_cow_block() to\nbtrfs_force_cow_block() before the COWed extent buffer is freed.\nThis also has a side effect of invoking the tracepoint in the tree defrag\ncode, at defrag.c:btrfs_realloc_node(), since btrfs_force_cow_block() is\ncalled there, but this is fine and it was actually missing there.",
  "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-2024-56759"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/ba5120a2fb5f23b4d39d302e181aa5d4e28a90d1"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/526ff5b27f090fb15040471f892cd2c9899ce314"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/66376f1a73cba57fd0af2631d7888605b738e499"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/9a466b8693b9add05de99af00c7bdff8259ecf19"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/c3a403d8ce36f5a809a492581de5ad17843e4701"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/44f52bbe96dfdbe4aca3818a2534520082a07040"
    }
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  "database_specific": {
    "source": "https://git.kernel.org/pub/scm/linux/security/vulns.git",
    "upstream_modified": "2026-08-05T11:52:36Z",
    "severity": {
      "source": "kernel CNA",
      "cvss_v3_score": 7.8,
      "cvss_v3_severity": "High",
      "scenario": "AV:L - The vulnerable code is btrfs's core b-tree COW path, reached through ordinary filesystem syscalls (write, create, unlink, rename) on a mounted btrfs volume. This requires local access to the system; there is no network protocol handler involved.\nAC:L - The attacker fully controls the triggering side \u2014 every metadata modification calls btrfs_search_slot() \u2192 btrfs_cow_block(), so the free-then-trace window can be retried millions of times, and the attacker can raise CPU/scheduling pressure with concurrent threads to make preemption at that point (and elapse of the RCU grace period) occur. A race the attacker can drive at will and retry unboundedly is Low complexity.\nPR:L - Only an unprivileged local account with write access to any btrfs filesystem is needed; no capability, CAP_SYS_ADMIN, or namespace check exists anywhere on the btrfs_search_slot() \u2192 btrfs_cow_block() path. Writing into a home directory or container rootfs on btrfs is sufficient.\nUI:N - The attacker triggers the COW path directly with its own filesystem operations; no victim action, mount, or file-open by another user is required.\nS:U - The use-after-free is confined to kernel memory managed by the same kernel security authority; there is no VM, IOMMU, or sandbox boundary crossed.\nC:H - The freed extent_buffer is read after release from a mergeable, non-TYPESAFE_BY_RCU slab cache, and btrfs_header_level(buf) loads eb->folios[0] and dereferences it \u2014 with heap spray this becomes a controlled-address read whose result is emitted into the trace ring buffer, disclosing kernel memory.\nI:H - The use-after-free on a reclaimable, slab-mergeable object gives the attacker influence over the contents of the reused allocation and the pointer subsequently dereferenced, which is the standard primitive for escalating a UAF into kernel memory corruption and control-flow hijacking.\nA:H - Dereferencing the freed extent_buffer and its stale folios[0] pointer causes a wild-pointer access that oopses or panics the kernel (this is exactly what syzbot's KASAN report captured), and it can be re-triggered repeatedly."
    }
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}