CVE-2026-31787 (GCVE-0-2026-31787)
Vulnerability from cvelistv5
Published
2026-04-30 10:31
Modified
2026-06-14 17:44
Severity ?
Summary
In the Linux kernel, the following vulnerability has been resolved: xen/privcmd: fix double free via VMA splitting privcmd_vm_ops defines .close (privcmd_close), but neither .may_split nor .open. When userspace does a partial munmap() on a privcmd mapping, the kernel splits the VMA via __split_vma(). Since may_split is NULL, the split is allowed. vm_area_dup() copies vm_private_data (a pages array allocated in alloc_empty_pages()) into the new VMA without any fixup, because there is no .open callback. Both VMAs now point to the same pages array. When the unmapped portion is closed, privcmd_close() calls: - xen_unmap_domain_gfn_range() - xen_free_unpopulated_pages() - kvfree(pages) The surviving VMA still holds the dangling pointer. When it is later destroyed, the same sequence runs again, which leads to a double free. Fix this issue by adding a .may_split callback denying the VMA split. This is XSA-487 / CVE-2026-31787
References
Impacted products
Vendor Product Version
Linux Linux Version: d71f513985c22f1050295d1a7e4327cf9fb060da
Version: d71f513985c22f1050295d1a7e4327cf9fb060da
Version: d71f513985c22f1050295d1a7e4327cf9fb060da
Version: d71f513985c22f1050295d1a7e4327cf9fb060da
Version: d71f513985c22f1050295d1a7e4327cf9fb060da
Version: d71f513985c22f1050295d1a7e4327cf9fb060da
Version: d71f513985c22f1050295d1a7e4327cf9fb060da
Version: d71f513985c22f1050295d1a7e4327cf9fb060da
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          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nxen/privcmd: fix double free via VMA splitting\n\nprivcmd_vm_ops defines .close (privcmd_close), but neither .may_split\nnor .open. When userspace does a partial munmap() on a privcmd mapping,\nthe kernel splits the VMA via __split_vma(). Since may_split is NULL,\nthe split is allowed. vm_area_dup() copies vm_private_data (a pages\narray allocated in alloc_empty_pages()) into the new VMA without any\nfixup, because there is no .open callback.\n\nBoth VMAs now point to the same pages array. When the unmapped portion\nis closed, privcmd_close() calls:\n    - xen_unmap_domain_gfn_range()\n    - xen_free_unpopulated_pages()\n    - kvfree(pages)\n\nThe surviving VMA still holds the dangling pointer. When it is later\ndestroyed, the same sequence runs again, which leads to a double free.\n\nFix this issue by adding a .may_split callback denying the VMA split.\n\nThis is XSA-487 / CVE-2026-31787"
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