{"api_version":"1","generated_at":"2026-07-24T00:44:18+00:00","cve":"CVE-2026-63950","urls":{"html":"https://cve.report/CVE-2026-63950","api":"https://cve.report/api/cve/CVE-2026-63950.json","docs":"https://cve.report/api","cve_org":"https://www.cve.org/CVERecord?id=CVE-2026-63950","nvd":"https://nvd.nist.gov/vuln/detail/CVE-2026-63950"},"summary":{"title":"mm/rmap: initialize nr_pages to 1 at loop start in try_to_unmap_one","description":"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.","state":"PUBLISHED","assigner":"Linux","published_at":"2026-07-19 16:17:13","updated_at":"2026-07-20 15:16:58"},"problem_types":[],"metrics":[{"version":"3.1","source":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","type":"Secondary","score":"7.8","severity":"HIGH","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","data":{"version":"3.1","vectorString":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","baseScore":7.8,"baseSeverity":"HIGH","attackVector":"LOCAL","attackComplexity":"LOW","privilegesRequired":"LOW","userInteraction":"NONE","scope":"UNCHANGED","confidentialityImpact":"HIGH","integrityImpact":"HIGH","availabilityImpact":"HIGH"}},{"version":"3.1","source":"CNA","type":"DECLARED","score":"7.8","severity":"HIGH","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","data":{"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"}}],"references":[{"url":"https://git.kernel.org/stable/c/f611db9b771b2b6775357555d2517af044fca4f0","name":"https://git.kernel.org/stable/c/f611db9b771b2b6775357555d2517af044fca4f0","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/3f8968e9cbf95d5d87d32218906cab0b9b9eddbe","name":"https://git.kernel.org/stable/c/3f8968e9cbf95d5d87d32218906cab0b9b9eddbe","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/0fcc34d0d8fefca4fea349e45c10e3a3d90350eb","name":"https://git.kernel.org/stable/c/0fcc34d0d8fefca4fea349e45c10e3a3d90350eb","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://www.cve.org/CVERecord?id=CVE-2026-63950","name":"CVE Program record","refsource":"CVE.ORG","tags":["canonical"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-63950","name":"NVD vulnerability detail","refsource":"NVD","tags":["canonical","analysis"]}],"affected":[{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 354dffd29575cdf13154e8fb787322354aa9efc4 0fcc34d0d8fefca4fea349e45c10e3a3d90350eb git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 354dffd29575cdf13154e8fb787322354aa9efc4 f611db9b771b2b6775357555d2517af044fca4f0 git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 354dffd29575cdf13154e8fb787322354aa9efc4 3f8968e9cbf95d5d87d32218906cab0b9b9eddbe git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 6.15","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 6.15 semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 6.18.35 6.18.* semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 7.0.12 7.0.* semver","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"unaffected 7.1 * original_commit_for_fix","platforms":[]}],"timeline":[],"solutions":[],"workarounds":[],"exploits":[],"credits":[],"nvd_cpes":[],"vendor_comments":[],"enrichments":{"kev":null,"epss":{"cve_year":"2026","cve_id":"63950","cve":"CVE-2026-63950","epss":"0.001980000","percentile":"0.097880000","score_date":"2026-07-20","updated_at":"2026-07-21 00:13:13"},"legacy_qids":[]},"source_records":{"cve_program":{"containers":{"cna":{"affected":[{"defaultStatus":"unaffected","product":"Linux","programFiles":["mm/rmap.c"],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","vendor":"Linux","versions":[{"lessThan":"0fcc34d0d8fefca4fea349e45c10e3a3d90350eb","status":"affected","version":"354dffd29575cdf13154e8fb787322354aa9efc4","versionType":"git"},{"lessThan":"f611db9b771b2b6775357555d2517af044fca4f0","status":"affected","version":"354dffd29575cdf13154e8fb787322354aa9efc4","versionType":"git"},{"lessThan":"3f8968e9cbf95d5d87d32218906cab0b9b9eddbe","status":"affected","version":"354dffd29575cdf13154e8fb787322354aa9efc4","versionType":"git"}]},{"defaultStatus":"affected","product":"Linux","programFiles":["mm/rmap.c"],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","vendor":"Linux","versions":[{"status":"affected","version":"6.15"},{"lessThan":"6.15","status":"unaffected","version":"0","versionType":"semver"},{"lessThanOrEqual":"6.18.*","status":"unaffected","version":"6.18.35","versionType":"semver"},{"lessThanOrEqual":"7.0.*","status":"unaffected","version":"7.0.12","versionType":"semver"},{"lessThanOrEqual":"*","status":"unaffected","version":"7.1","versionType":"original_commit_for_fix"}]}],"cpeApplicability":[{"nodes":[{"cpeMatch":[{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"6.18.35","versionStartIncluding":"6.15","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"7.0.12","versionStartIncluding":"6.15","vulnerable":true},{"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionEndExcluding":"7.1","versionStartIncluding":"6.15","vulnerable":true}],"negate":false,"operator":"OR"}]}],"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."}],"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"}}],"providerMetadata":{"dateUpdated":"2026-07-20T13:41:49.078Z","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","shortName":"Linux"},"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"}}},"cveMetadata":{"assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","assignerShortName":"Linux","cveId":"CVE-2026-63950","datePublished":"2026-07-19T14:55:43.404Z","dateReserved":"2026-07-19T07:54:57.023Z","dateUpdated":"2026-07-20T13:41:49.078Z","state":"PUBLISHED"},"dataType":"CVE_RECORD","dataVersion":"5.2"},"nvd":{"publishedDate":"2026-07-19 16:17:13","lastModifiedDate":"2026-07-20 15:16:58","problem_types":[],"metrics":{"cvssMetricV31":[{"source":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","type":"Secondary","cvssData":{"version":"3.1","vectorString":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","baseScore":7.8,"baseSeverity":"HIGH","attackVector":"LOCAL","attackComplexity":"LOW","privilegesRequired":"LOW","userInteraction":"NONE","scope":"UNCHANGED","confidentialityImpact":"HIGH","integrityImpact":"HIGH","availabilityImpact":"HIGH"},"exploitabilityScore":1.8,"impactScore":5.9}]},"configurations":[]},"legacy_mitre":{"record":{"CveYear":"2026","CveId":"63950","Ordinal":"1","Title":"mm/rmap: initialize nr_pages to 1 at loop start in try_to_unmap_","CVE":"CVE-2026-63950","Year":"2026"},"notes":[{"CveYear":"2026","CveId":"63950","Ordinal":"1","NoteData":"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.","Type":"Description","Title":"mm/rmap: initialize nr_pages to 1 at loop start in try_to_unmap_"}]}}}