{
  "schema_version": "1.6.1",
  "id": "RPI-CVE-2025-22015",
  "modified": "2026-10-09T11:39:44Z",
  "upstream": [
    "CVE-2025-22015"
  ],
  "published": "2025-04-08T08:16:52Z",
  "summary": "mm/migrate: fix shmem xarray update during migration",
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nmm/migrate: fix shmem xarray update during migration\n\nA shmem folio can be either in page cache or in swap cache, but not at the\nsame time.  Namely, once it is in swap cache, folio->mapping should be\nNULL, and the folio is no longer in a shmem mapping.\n\nIn __folio_migrate_mapping(), to determine the number of xarray entries to\nupdate, folio_test_swapbacked() is used, but that conflates shmem in page\ncache case and shmem in swap cache case.  It leads to xarray multi-index\nentry corruption, since it turns a sibling entry to a normal entry during\nxas_store() (see [1] for a userspace reproduction).  Fix it by only using\nfolio_test_swapcache() to determine whether xarray is storing swap cache\nentries or not to choose the right number of xarray entries to update.\n\n[1] https://lore.kernel.org/linux-mm/Z8idPCkaJW1IChjT@casper.infradead.org/\n\nNote:\nIn __split_huge_page(), folio_test_anon() && folio_test_swapcache() is\nused to get swap_cache address space, but that ignores the shmem folio in\nswap cache case.  It could lead to NULL pointer dereferencing when a\nin-swap-cache shmem folio is split at __xa_store(), since\n!folio_test_anon() is true and folio->mapping is NULL.  But fortunately,\nits caller split_huge_page_to_list_to_order() bails out early with EBUSY\nwhen folio->mapping is NULL.  So no need to take care of it here.",
  "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-2025-22015"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/49100c0b070e900f87c8fac3be9b9ef8a30fa673"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/29124ae980e2860f0eec7355949d3d3292ee81da"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/c057ee03f751d6cecf7ee64f52f6545d94082aaa"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/75cfb92eb63298d717b6b0118f91ba12c4fcfeb5"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/60cf233b585cdf1f3c5e52d1225606b86acd08b0"
    }
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  "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 vulnerability is reached entirely through local syscalls \u2014 mounting tmpfs with huge=always, populating a large shmem folio, then mbind(MPOL_MF_MOVE)/move_pages()/madvise(MADV_PAGEOUT). There is no network-facing path into mm/migrate.c.\nAC:L - The corruption is deterministic, not a race: once a large shmem page-cache folio is migrated, folio_test_swapbacked() unconditionally selects the wrong entry count and the sibling entries are destroyed every time. The attacker creates all preconditions (the huge tmpfs mount, the folio, the migration, and the subsequent swapout) with no dependence on external state.\nPR:L - An ordinary unprivileged user suffices \u2014 tmpfs is FS_USERNS_MOUNT and its huge= option has no capability check (mm/shmem.c:4475), so a user namespace supplies large shmem folios, and migrating one's own pages requires no capability (only MPOL_MF_MOVE_ALL checks CAP_SYS_NICE). No root or real CAP_* in the init namespace is needed.\nUI:N - The attacking process performs every step itself \u2014 mount, allocate, migrate, swap out, and re-access. No victim action or cooperating process is involved.\nS:U - The corrupted xarray, the freed folio, and the resulting memory access all live within the kernel's own security authority. No VM, IOMMU, or sandbox boundary is crossed.\nC:H - After swapout frees the folio, nr-1 dangling pointers remain in the shmem page cache; once the page is reallocated the attacker reads it back through their own tmpfs file via read() or mmap, disclosing memory now owned by other processes, slab, or page tables.\nI:H - The same dangling page-cache entries are writable \u2014 write()/mmap on the tmpfs file modifies a page the allocator has handed to another owner, giving an arbitrary kernel-memory write primitive suitable for privilege escalation.\nA:H - filemap_get_entry() loops forever under rcu_read_lock() when folio_try_get() keeps failing on the zero-refcount folio, producing a soft lockup; BUG_ON(error) in shmem_delete_from_page_cache() and the VM_BUG_ON_FOLIO checks give additional panic/oops paths."
    }
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}