{
  "schema_version": "1.6.1",
  "id": "RPI-CVE-2026-31648",
  "modified": "2026-10-07T17:22:01Z",
  "upstream": [
    "CVE-2026-31648"
  ],
  "published": "2026-04-24T14:47:31Z",
  "summary": "mm: filemap: fix nr_pages calculation overflow in filemap_map_pages()",
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nmm: filemap: fix nr_pages calculation overflow in filemap_map_pages()\n\nWhen running stress-ng on my Arm64 machine with v7.0-rc3 kernel, I\nencountered some very strange crash issues showing up as \"Bad page state\":\n\n\"\n[  734.496287] BUG: Bad page state in process stress-ng-env  pfn:415735fb\n[  734.496427] page: refcount:0 mapcount:1 mapping:0000000000000000 index:0x4cf316 pfn:0x415735fb\n[  734.496434] flags: 0x57fffe000000800(owner_2|node=1|zone=2|lastcpupid=0x3ffff)\n[  734.496439] raw: 057fffe000000800 0000000000000000 dead000000000122 0000000000000000\n[  734.496440] raw: 00000000004cf316 0000000000000000 0000000000000000 0000000000000000\n[  734.496442] page dumped because: nonzero mapcount\n\"\n\nAfter analyzing this page\u2019s state, it is hard to understand why the\nmapcount is not 0 while the refcount is 0, since this page is not where\nthe issue first occurred.  By enabling the CONFIG_DEBUG_VM config, I can\nreproduce the crash as well and captured the first warning where the issue\nappears:\n\n\"\n[  734.469226] page: refcount:33 mapcount:0 mapping:00000000bef2d187 index:0x81a0 pfn:0x415735c0\n[  734.469304] head: order:5 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0\n[  734.469315] memcg:ffff000807a8ec00\n[  734.469320] aops:ext4_da_aops ino:100b6f dentry name(?):\"stress-ng-mmaptorture-9397-0-2736200540\"\n[  734.469335] flags: 0x57fffe400000069(locked|uptodate|lru|head|node=1|zone=2|lastcpupid=0x3ffff)\n......\n[  734.469364] page dumped because: VM_WARN_ON_FOLIO((_Generic((page + nr_pages - 1),\nconst struct page *: (const struct folio *)_compound_head(page + nr_pages - 1), struct page *:\n(struct folio *)_compound_head(page + nr_pages - 1))) != folio)\n[  734.469390] ------------[ cut here ]------------\n[  734.469393] WARNING: ./include/linux/rmap.h:351 at folio_add_file_rmap_ptes+0x3b8/0x468,\nCPU#90: stress-ng-mlock/9430\n[  734.469551]  folio_add_file_rmap_ptes+0x3b8/0x468 (P)\n[  734.469555]  set_pte_range+0xd8/0x2f8\n[  734.469566]  filemap_map_folio_range+0x190/0x400\n[  734.469579]  filemap_map_pages+0x348/0x638\n[  734.469583]  do_fault_around+0x140/0x198\n......\n[  734.469640]  el0t_64_sync+0x184/0x188\n\"\n\nThe code that triggers the warning is: \"VM_WARN_ON_FOLIO(page_folio(page +\nnr_pages - 1) != folio, folio)\", which indicates that set_pte_range()\ntried to map beyond the large folio\u2019s size.\n\nBy adding more debug information, I found that 'nr_pages' had overflowed\nin filemap_map_pages(), causing set_pte_range() to establish mappings for\na range exceeding the folio size, potentially corrupting fields of pages\nthat do not belong to this folio (e.g., page->_mapcount).\n\nAfter above analysis, I think the possible race is as follows:\n\nCPU 0                                                  CPU 1\nfilemap_map_pages()                                   ext4_setattr()\n   //get and lock folio with old inode->i_size\n   next_uptodate_folio()\n\n                                                          .......\n                                                          //shrink the inode->i_size\n                                                          i_size_write(inode, attr->ia_size);\n\n   //calculate the end_pgoff with the new inode->i_size\n   file_end = DIV_ROUND_UP(i_size_read(mapping->host), PAGE_SIZE) - 1;\n   end_pgoff = min(end_pgoff, file_end);\n\n   ......\n   //nr_pages can be overflowed, cause xas.xa_index > end_pgoff\n   end = folio_next_index(folio) - 1;\n   nr_pages = min(end, end_pgoff) - xas.xa_index + 1;\n\n   ......\n   //map large folio\n   filemap_map_folio_range()\n                                                          ......\n                                                          //truncate folios\n                                                          truncate_pagecache(inode, inode->i_size);\n\nTo fix this issue, move the 'end_pgoff' calculation before\nnext_uptodate_folio(), so the retrieved folio stays consistent with the\nfile end to avoid \n---truncated---",
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  "references": [
    {
      "type": "ADVISORY",
      "url": "https://www.cve.org/CVERecord?id=CVE-2026-31648"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/88591194df736a508dd5461ab2167a61e98caac1"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/633ab680c405ac390e6bec5b74aaf46197c837b6"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/576543bedd616254032d4ebe54a90076f9e31740"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/9316a820b9aae07d44469d6485376dad824c5b3f"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/f58df566524ebcdfa394329c64f47e3c9257516e"
    }
  ],
  "database_specific": {
    "source": "https://git.kernel.org/pub/scm/linux/security/vulns.git",
    "upstream_modified": "2026-08-05T13:16:28Z"
  }
}