CVE-2025-40006 (GCVE-0-2025-40006)
Vulnerability from cvelistv5
Published
2025-10-20 15:26
Modified
2026-08-05 12:07
Severity ?
7.8 (High) - CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Summary
In the Linux kernel, the following vulnerability has been resolved: mm/hugetlb: fix folio is still mapped when deleted Migration may be raced with fallocating hole. remove_inode_single_folio will unmap the folio if the folio is still mapped. However, it's called without folio lock. If the folio is migrated and the mapped pte has been converted to migration entry, folio_mapped() returns false, and won't unmap it. Due to extra refcount held by remove_inode_single_folio, migration fails, restores migration entry to normal pte, and the folio is mapped again. As a result, we triggered BUG in filemap_unaccount_folio. The log is as follows: BUG: Bad page cache in process hugetlb pfn:156c00 page: refcount:515 mapcount:0 mapping:0000000099fef6e1 index:0x0 pfn:0x156c00 head: order:9 mapcount:1 entire_mapcount:1 nr_pages_mapped:0 pincount:0 aops:hugetlbfs_aops ino:dcc dentry name(?):"my_hugepage_file" flags: 0x17ffffc00000c1(locked|waiters|head|node=0|zone=2|lastcpupid=0x1fffff) page_type: f4(hugetlb) page dumped because: still mapped when deleted CPU: 1 UID: 0 PID: 395 Comm: hugetlb Not tainted 6.17.0-rc5-00044-g7aac71907bde-dirty #484 NONE Hardware name: QEMU Ubuntu 24.04 PC (i440FX + PIIX, 1996), BIOS 0.0.0 02/06/2015 Call Trace: <TASK> dump_stack_lvl+0x4f/0x70 filemap_unaccount_folio+0xc4/0x1c0 __filemap_remove_folio+0x38/0x1c0 filemap_remove_folio+0x41/0xd0 remove_inode_hugepages+0x142/0x250 hugetlbfs_fallocate+0x471/0x5a0 vfs_fallocate+0x149/0x380 Hold folio lock before checking if the folio is mapped to avold race with migration.
References
Impacted products
Vendor Product Version
Linux Linux Version: 4aae8d1c051ea00b456da6811bc36d1f69de5445
Version: 4aae8d1c051ea00b456da6811bc36d1f69de5445
Version: 4aae8d1c051ea00b456da6811bc36d1f69de5445
Version: 4aae8d1c051ea00b456da6811bc36d1f69de5445
Version: 4aae8d1c051ea00b456da6811bc36d1f69de5445
Version: 4aae8d1c051ea00b456da6811bc36d1f69de5445
Version: 4aae8d1c051ea00b456da6811bc36d1f69de5445
Version: 4aae8d1c051ea00b456da6811bc36d1f69de5445
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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "fs/hugetlbfs/inode.c"
          ],
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          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
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              "version": "0",
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            },
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              "status": "unaffected",
              "version": "6.17",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
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              ],
              "negate": false,
              "operator": "OR"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nmm/hugetlb: fix folio is still mapped when deleted\n\nMigration may be raced with fallocating hole.  remove_inode_single_folio\nwill unmap the folio if the folio is still mapped.  However, it\u0027s called\nwithout folio lock.  If the folio is migrated and the mapped pte has been\nconverted to migration entry, folio_mapped() returns false, and won\u0027t\nunmap it.  Due to extra refcount held by remove_inode_single_folio,\nmigration fails, restores migration entry to normal pte, and the folio is\nmapped again.  As a result, we triggered BUG in filemap_unaccount_folio.\n\nThe log is as follows:\n BUG: Bad page cache in process hugetlb  pfn:156c00\n page: refcount:515 mapcount:0 mapping:0000000099fef6e1 index:0x0 pfn:0x156c00\n head: order:9 mapcount:1 entire_mapcount:1 nr_pages_mapped:0 pincount:0\n aops:hugetlbfs_aops ino:dcc dentry name(?):\"my_hugepage_file\"\n flags: 0x17ffffc00000c1(locked|waiters|head|node=0|zone=2|lastcpupid=0x1fffff)\n page_type: f4(hugetlb)\n page dumped because: still mapped when deleted\n CPU: 1 UID: 0 PID: 395 Comm: hugetlb Not tainted 6.17.0-rc5-00044-g7aac71907bde-dirty #484 NONE\n Hardware name: QEMU Ubuntu 24.04 PC (i440FX + PIIX, 1996), BIOS 0.0.0 02/06/2015\n Call Trace:\n  \u003cTASK\u003e\n  dump_stack_lvl+0x4f/0x70\n  filemap_unaccount_folio+0xc4/0x1c0\n  __filemap_remove_folio+0x38/0x1c0\n  filemap_remove_folio+0x41/0xd0\n  remove_inode_hugepages+0x142/0x250\n  hugetlbfs_fallocate+0x471/0x5a0\n  vfs_fallocate+0x149/0x380\n\nHold folio lock before checking if the folio is mapped to avold race with\nmigration."
        }
      ],
      "metrics": [
        {
          "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"
          },
          "scenarios": [
            {
              "lang": "en",
              "value": "AV:L - Exploitation requires local syscalls only \u2014 `memfd_create(MFD_HUGETLB)`/`mmap` plus `fallocate(FALLOC_FL_PUNCH_HOLE)` racing against `mbind`/`move_pages`. There is no network-reachable path into hugetlbfs fallocate.\nAC:L - The attacker controls both sides of the race with its own threads \u2014 one looping on punch-hole, the other looping on NUMA migration of the same mapping \u2014 and can retry indefinitely at no cost until the window is hit. Per race-condition guidance, attacker-driven races are Low.\nPR:L - `memfd_create(MFD_HUGETLB)` uses HUGETLB_ANONHUGE_INODE and bypasses the `can_do_hugetlb_shm()`/CAP_IPC_LOCK check entirely, and `MPOL_MF_MOVE` on one\u0027s own address space needs no capability, so an ordinary unprivileged local user can reach the whole path.\nUI:N - The attacking process performs every step itself; no victim action, mount, or file open by another user is needed.\nS:U - The vulnerable code and the corrupted resources are both in the host kernel\u0027s memory management, so the impact stays within a single security authority despite the severity.\nC:H - The huge page is unlinked from the page cache with its `mapping` cleared while the attacker retains writable PTEs, and hugetlb folios are explicitly excluded from `filemap_unaccount_folio()`\u0027s recovery heuristic \u2014 leaving a stale mapping to a 2MB page the kernel may recycle to another process, container, or hugepage-backed KVM guest, yielding arbitrary read of that memory.\nI:H - The same stale writable mapping gives an arbitrary-write primitive over whatever the kernel later places in that recycled huge page, and the hugetlb reserve/subpool counters are decremented for a page still in use, corrupting pool accounting \u2014 memory corruption of this class is leveragable for control-flow hijack.\nA:H - The bug\u0027s directly observed symptom is the `BUG: Bad page cache ... still mapped when deleted` report, which is a hard `VM_BUG_ON_FOLIO()` panic under CONFIG_DEBUG_VM and a `TAINT_BAD_PAGE` plus unrecoverable page-cache/hugetlb-pool corruption otherwise, repeatable at will by an unprivileged user."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-05T12:07:03.344Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/bc1c9ce8aeff45318332035dbef9713fb9e982d7"
        },
        {
          "url": "https://git.kernel.org/stable/c/91f548e920fbf8be3f285bfa3fa045ae017e836d"
        },
        {
          "url": "https://git.kernel.org/stable/c/3e851448078f5b01f6264915df3cfef75e323a12"
        },
        {
          "url": "https://git.kernel.org/stable/c/c1dc0524ab2cc3982d4e0d2bfac71a0cd4d65c39"
        },
        {
          "url": "https://git.kernel.org/stable/c/c9c2a51f91aea70e89b496cac360cd795a2b3c26"
        },
        {
          "url": "https://git.kernel.org/stable/c/910d7749346c4b0acdc6e4adfdc4a9984281a206"
        },
        {
          "url": "https://git.kernel.org/stable/c/21ee79ce938127f88fe07e409c1817f477dbe7ea"
        },
        {
          "url": "https://git.kernel.org/stable/c/7b7387650dcf2881fd8bb55bcf3c8bd6c9542dd7"
        }
      ],
      "title": "mm/hugetlb: fix folio is still mapped when deleted",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2025-40006",
    "datePublished": "2025-10-20T15:26:53.097Z",
    "dateReserved": "2025-04-16T07:20:57.151Z",
    "dateUpdated": "2026-08-05T12:07:03.344Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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