{"cve":"CVE-2026-68086","nvd":{"published":"2026-08-10T12:17:21.207","modified":"2026-08-10T12:17:21.207","status":"Received","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nmm/khugepaged: write all dirty file folios when collapsing\n\n[There is no upstream commit, as this code was removed by upstream\n commit 044925f9b565 (\"mm: fs: remove filemap_nr_thps*() functions and their users\")]\n\nAs-is, khugepaged and writable-file opening exclude each other. A file\ncannot be open writeable and have THPs (because the filesystem is not aware\nof them). khugepaged will never collapse file pages for files that are\nopened writeable. On an open(O_RDWR/O_WRONLY), the page cache for that\nparticular file is dropped. This is fine because nothing could've been\ndirtied.\n\nHowever, there is an edge-case: collapse_file() might not be able to\ncoexist with concurrent writers, but it can coexist with dirty folios\n(from previous writers). Therefore, the following can happen:\n\nopen(file, O_RDWR)\nwrite(file)\nclose(file)\nmadvise(file_mapping, MADV_COLLAPSE, some non-dirty range)\nopen(file, O_RDWR)\n nr_thps > 0\n  truncate_inode_pages()\n    /* THPs are cleared out, but so are the dirty folios */\n\nWhen this edge-case happens, there is data loss, as the dirty folios are\nfully discarded.\n\nFix it by fully writing back the page cache (and waiting) when collapsing\nfile THPs. Doing so provides the guarantee that no dirty folio will be\nobserved while there are active THPs. To fully ensure this is safe, the\ninvalidate_lock needs to be held while doing the writeout, so that\ndo_dentry_open()'s page cache truncation excludes this write-and-wait.\n\nAs a side effect, move the nr_thps counter bumping outside the i_pages\nlock. This is correct since the counter itself is an atomic_t and the\nproducer <-> consumer correctness is provided by a full memory barrier:\nsmp_mb() in collapse_file()/memory barrier implied by full ordering in\nget_write_access() -> atomic_inc_unless_negative().","cvss_v4":null,"cvss_v3":null,"cwes":[],"references":["https://git.kernel.org/stable/c/2dfe9f5c91d0963058f8a5e46e1c2a908382cc46"],"products":[],"source":"nvd","synced_at":"2026-10-19T22:47:54.990491175+00:00"},"epss":{"cve":"CVE-2026-68086","score":0.0015,"percentile":0.04117,"date":"2026-10-31"},"kev":null,"osv":[],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}