{"dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": {"cveId": "CVE-2026-63950", "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "state": "PUBLISHED", "assignerShortName": "Linux", "dateReserved": "2026-07-19T07:54:57.023Z", "datePublished": "2026-07-19T14:55:43.404Z", "dateUpdated": "2026-07-19T14:55:43.404Z"}, "containers": {"cna": {"providerMetadata": {"orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "shortName": "Linux", "dateUpdated": "2026-07-19T14:55:43.404Z"}, "descriptions": [{"lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nmm/rmap: initialize nr_pages to 1 at loop start in try_to_unmap_one\n\nInitialize nr_pages to 1 at the start of each loop iteration, like\nfolio_referenced_one() does.\n\nWithout this, nr_pages computed by a previous folio_unmap_pte_batch() call\ncan be reused on a later iteration that does not run\nfolio_unmap_pte_batch() again.\n\nmmap a 64K large folio with MAP_ANONYMOUS | MAP_DROPPABLE, then call\nmadvise(MADV_FREE), then make the last page device-exclusive via\nHMM_DMIRROR_EXCLUSIVE.\n\nTrigger node reclaim through sysfs. Now, in try_to_unmap_one(), we will\nfirst clear the first 15 out of 16 entries mapping the lazyfree folio. \nThis will set nr_pages to 15. In the next pvmw walk, this nr_pages gets\nreused on a device-exclusive pte, thus potentially corrupting folio\nrefcount/mapcount.\n\nAt the moment, I have a userspace program which can make the kernel spit\nout a trace, but the blow up is in folio_referenced_one(), because there\nare existing bugs in the interaction between device-private and rmap\n(which too I am investigating). I did a one liner kernel change to avoid\ngoing into folio_referenced_one(), and the kernel blows up at\nfolio_remove_rmap_ptes in try_to_unmap_one which is what I wanted.\n\nNote that the bug is there not since file folio batching but lazyfree\nfolio batching, since device-exclusive only works for anonymous folios.\n\nUserspace visible effect is simply kernel crashing somewhere due to\nrefcount/mapcount corruption."}], "affected": [{"product": "Linux", "vendor": "Linux", "defaultStatus": "unaffected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": ["mm/rmap.c"], "versions": [{"version": "354dffd29575cdf13154e8fb787322354aa9efc4", "lessThan": "0fcc34d0d8fefca4fea349e45c10e3a3d90350eb", "status": "affected", "versionType": "git"}, {"version": "354dffd29575cdf13154e8fb787322354aa9efc4", "lessThan": "f611db9b771b2b6775357555d2517af044fca4f0", "status": "affected", "versionType": "git"}, {"version": "354dffd29575cdf13154e8fb787322354aa9efc4", "lessThan": "3f8968e9cbf95d5d87d32218906cab0b9b9eddbe", "status": "affected", "versionType": "git"}]}, {"product": "Linux", "vendor": "Linux", "defaultStatus": "affected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": ["mm/rmap.c"], "versions": [{"version": "6.15", "status": "affected"}, {"version": "0", "lessThan": "6.15", "status": "unaffected", "versionType": "semver"}, {"version": "6.18.35", "lessThanOrEqual": "6.18.*", "status": "unaffected", "versionType": "semver"}, {"version": "7.0.12", "lessThanOrEqual": "7.0.*", "status": "unaffected", "versionType": "semver"}, {"version": "7.1", "lessThanOrEqual": "*", "status": "unaffected", "versionType": "original_commit_for_fix"}]}], "cpeApplicability": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.15", "versionEndExcluding": "6.18.35"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.15", "versionEndExcluding": "7.0.12"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.15", "versionEndExcluding": "7.1"}]}]}], "references": [{"url": "https://git.kernel.org/stable/c/0fcc34d0d8fefca4fea349e45c10e3a3d90350eb"}, {"url": "https://git.kernel.org/stable/c/f611db9b771b2b6775357555d2517af044fca4f0"}, {"url": "https://git.kernel.org/stable/c/3f8968e9cbf95d5d87d32218906cab0b9b9eddbe"}], "title": "mm/rmap: initialize nr_pages to 1 at loop start in try_to_unmap_one", "x_generator": {"engine": "bippy-1.2.0"}}}}

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