{
  "schema_version": "1.6.1",
  "id": "RPI-CVE-2025-21709",
  "modified": "2026-10-09T11:39:44Z",
  "upstream": [
    "CVE-2025-21709"
  ],
  "published": "2025-02-27T02:06:37Z",
  "summary": "kernel: be more careful about dup_mmap() failures and uprobe registering",
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nkernel: be more careful about dup_mmap() failures and uprobe registering\n\nIf a memory allocation fails during dup_mmap(), the maple tree can be left\nin an unsafe state for other iterators besides the exit path.  All the\nlocks are dropped before the exit_mmap() call (in mm/mmap.c), but the\nincomplete mm_struct can be reached through (at least) the rmap finding\nthe vmas which have a pointer back to the mm_struct.\n\nUp to this point, there have been no issues with being able to find an\nmm_struct that was only partially initialised.  Syzbot was able to make\nthe incomplete mm_struct fail with recent forking changes, so it has been\nproven unsafe to use the mm_struct that hasn't been initialised, as\nreferenced in the link below.\n\nAlthough 8ac662f5da19f (\"fork: avoid inappropriate uprobe access to\ninvalid mm\") fixed the uprobe access, it does not completely remove the\nrace.\n\nThis patch sets the MMF_OOM_SKIP to avoid the iteration of the vmas on the\noom side (even though this is extremely unlikely to be selected as an oom\nvictim in the race window), and sets MMF_UNSTABLE to avoid other potential\nusers from using a partially initialised mm_struct.\n\nWhen registering vmas for uprobe, skip the vmas in an mm that is marked\nunstable.  Modifying a vma in an unstable mm may cause issues if the mm\nisn't fully initialised.",
  "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-2025-21709"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/74c2471eb891a7dcb3874b21c106cda75f52be30"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/da139948aeda677ac09cc0e7d837f8a314de7d55"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/64c37e134b120fb462fb4a80694bfb8e7be77b14"
    }
  ],
  "database_specific": {
    "source": "https://git.kernel.org/pub/scm/linux/security/vulns.git",
    "upstream_modified": "2026-08-05T12:19:11Z",
    "severity": {
      "source": "kernel CNA",
      "cvss_v3_score": 7.8,
      "cvss_v3_severity": "High",
      "scenario": "AV:L - The corrupted mm_struct is produced by the fork()/clone() syscall path (dup_mmap()), which requires local execution on the target system. There is no remote or adjacent-network path to dup_mmap().\nAC:L - The attacker deterministically creates the unsafe mm by forking a process with many VMAs and delivering SIGKILL mid-dup_mmap() (the fatal_signal_pending() bail-out), or by forcing -ENOMEM under a memcg/RLIMIT_AS/overcommit limit, and can repeat this continuously to widen the window; the same attacker-generated memory pressure simultaneously activates the OOM killer/reaper that iterates the broken tree, so both sides of the race are attacker-driven.\nPR:L - Only the ability to call fork()/clone() and allocate memory is needed \u2014 any unprivileged local user or container process qualifies. No capability, namespace, or tracing privilege is required on the attacker's side.\nUI:N - The attacker triggers the failed fork and the resulting corrupted mm_struct entirely on their own; no victim action is required. The consuming iterators (uprobe registration, swapoff, OOM reaper) are background/system activity, not user interaction.\nS:U - The corruption and its consequences are confined to the kernel's own memory-management structures within the same security authority. No VM, IOMMU, or hypervisor boundary is crossed.\nC:H - The partially-initialised mm's maple tree hands out an internal XA_ZERO_ENTRY (0x406) as a struct vm_area_struct * and, past that point, live pointers to the parent process's VMAs, so iterators read through invalid pointers and operate with mm != vma->vm_mm \u2014 a cross-address-space mismatch that lets page-table walks touch another process's memory; a sibling CLONE_VM thread munmap()ing during the unlocked window turns those entries into dangling freed-object pointers, giving a use-after-free read primitive.\nI:H - install_breakpoint()/uprobe_write_opcode() modifies VMAs and page tables of an mm that is not fully initialised (exactly what the fix's check_stable_address_space() gate prevents), and the OOM reaper path guarded by the new MMF_OOM_SKIP would unmap the parent's VMAs through the child's mmu_gather, flushing the wrong mm's TLB and leaving stale writable mappings to freed pages \u2014 memory corruption usable for arbitrary write.\nA:H - The demonstrated failure is a kernel OOPS dereferencing XA_ZERO_ENTRY at a low address (the sibling swapoff fix records a fault at 0x446), fatal with panic_on_oops; in register_for_each_vma() the oops occurs while holding mmap_write_lock(mm) and percpu_down_write(&dup_mmap_sem), which are never released, hanging every subsequent fork() on the system."
    }
  }
}