FKIE_CVE-2026-31648

Vulnerability from fkie_nvd - Published: 2026-04-24 15:16 - Updated: 2026-04-24 17:51
Severity ?
Summary
In the Linux kernel, the following vulnerability has been resolved: mm: filemap: fix nr_pages calculation overflow in filemap_map_pages() When running stress-ng on my Arm64 machine with v7.0-rc3 kernel, I encountered some very strange crash issues showing up as "Bad page state": " [ 734.496287] BUG: Bad page state in process stress-ng-env pfn:415735fb [ 734.496427] page: refcount:0 mapcount:1 mapping:0000000000000000 index:0x4cf316 pfn:0x415735fb [ 734.496434] flags: 0x57fffe000000800(owner_2|node=1|zone=2|lastcpupid=0x3ffff) [ 734.496439] raw: 057fffe000000800 0000000000000000 dead000000000122 0000000000000000 [ 734.496440] raw: 00000000004cf316 0000000000000000 0000000000000000 0000000000000000 [ 734.496442] page dumped because: nonzero mapcount " After analyzing this page’s state, it is hard to understand why the mapcount is not 0 while the refcount is 0, since this page is not where the issue first occurred. By enabling the CONFIG_DEBUG_VM config, I can reproduce the crash as well and captured the first warning where the issue appears: " [ 734.469226] page: refcount:33 mapcount:0 mapping:00000000bef2d187 index:0x81a0 pfn:0x415735c0 [ 734.469304] head: order:5 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0 [ 734.469315] memcg:ffff000807a8ec00 [ 734.469320] aops:ext4_da_aops ino:100b6f dentry name(?):"stress-ng-mmaptorture-9397-0-2736200540" [ 734.469335] flags: 0x57fffe400000069(locked|uptodate|lru|head|node=1|zone=2|lastcpupid=0x3ffff) ...... [ 734.469364] page dumped because: VM_WARN_ON_FOLIO((_Generic((page + nr_pages - 1), const struct page *: (const struct folio *)_compound_head(page + nr_pages - 1), struct page *: (struct folio *)_compound_head(page + nr_pages - 1))) != folio) [ 734.469390] ------------[ cut here ]------------ [ 734.469393] WARNING: ./include/linux/rmap.h:351 at folio_add_file_rmap_ptes+0x3b8/0x468, CPU#90: stress-ng-mlock/9430 [ 734.469551] folio_add_file_rmap_ptes+0x3b8/0x468 (P) [ 734.469555] set_pte_range+0xd8/0x2f8 [ 734.469566] filemap_map_folio_range+0x190/0x400 [ 734.469579] filemap_map_pages+0x348/0x638 [ 734.469583] do_fault_around+0x140/0x198 ...... [ 734.469640] el0t_64_sync+0x184/0x188 " The code that triggers the warning is: "VM_WARN_ON_FOLIO(page_folio(page + nr_pages - 1) != folio, folio)", which indicates that set_pte_range() tried to map beyond the large folio’s size. By adding more debug information, I found that 'nr_pages' had overflowed in filemap_map_pages(), causing set_pte_range() to establish mappings for a range exceeding the folio size, potentially corrupting fields of pages that do not belong to this folio (e.g., page->_mapcount). After above analysis, I think the possible race is as follows: CPU 0 CPU 1 filemap_map_pages() ext4_setattr() //get and lock folio with old inode->i_size next_uptodate_folio() ....... //shrink the inode->i_size i_size_write(inode, attr->ia_size); //calculate the end_pgoff with the new inode->i_size file_end = DIV_ROUND_UP(i_size_read(mapping->host), PAGE_SIZE) - 1; end_pgoff = min(end_pgoff, file_end); ...... //nr_pages can be overflowed, cause xas.xa_index > end_pgoff end = folio_next_index(folio) - 1; nr_pages = min(end, end_pgoff) - xas.xa_index + 1; ...... //map large folio filemap_map_folio_range() ...... //truncate folios truncate_pagecache(inode, inode->i_size); To fix this issue, move the 'end_pgoff' calculation before next_uptodate_folio(), so the retrieved folio stays consistent with the file end to avoid ---truncated---
References
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/576543bedd616254032d4ebe54a90076f9e31740
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/633ab680c405ac390e6bec5b74aaf46197c837b6
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/88591194df736a508dd5461ab2167a61e98caac1
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/9316a820b9aae07d44469d6485376dad824c5b3f
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/f58df566524ebcdfa394329c64f47e3c9257516e
Impacted products
Vendor Product Version
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{
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "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 \u0027nr_pages\u0027 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-\u003e_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-\u003ei_size\n   next_uptodate_folio()\n\n                                                          .......\n                                                          //shrink the inode-\u003ei_size\n                                                          i_size_write(inode, attr-\u003eia_size);\n\n   //calculate the end_pgoff with the new inode-\u003ei_size\n   file_end = DIV_ROUND_UP(i_size_read(mapping-\u003ehost), PAGE_SIZE) - 1;\n   end_pgoff = min(end_pgoff, file_end);\n\n   ......\n   //nr_pages can be overflowed, cause xas.xa_index \u003e 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-\u003ei_size);\n\nTo fix this issue, move the \u0027end_pgoff\u0027 calculation before\nnext_uptodate_folio(), so the retrieved folio stays consistent with the\nfile end to avoid \n---truncated---"
    }
  ],
  "id": "CVE-2026-31648",
  "lastModified": "2026-04-24T17:51:40.810",
  "metrics": {},
  "published": "2026-04-24T15:16:44.193",
  "references": [
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/576543bedd616254032d4ebe54a90076f9e31740"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/633ab680c405ac390e6bec5b74aaf46197c837b6"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/88591194df736a508dd5461ab2167a61e98caac1"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/9316a820b9aae07d44469d6485376dad824c5b3f"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/f58df566524ebcdfa394329c64f47e3c9257516e"
    }
  ],
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
  "vulnStatus": "Awaiting Analysis"
}


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