CVE-2026-31787
Vulnerability Description
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
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
Vulnerability Details
Published Date
Last Modified
Source
NVD
Vendor
Linux
Product
Linux
External References
- https://git.kernel.org/stable/c/1576ff3869cbd3620717195f971c85b7d7fd62b5
- https://git.kernel.org/stable/c/2894a351fe2ea8684919d36df3188b9a35e3926f
- https://git.kernel.org/stable/c/2b985d3a024b9e8c24e21671b34e855569763808
- https://git.kernel.org/stable/c/402d84ad9e89bd4cbfd07ca8598532b7021daf95
- https://git.kernel.org/stable/c/446ee446d9ae66f36e95c3c90bbcc4e56b94cde0
- https://git.kernel.org/stable/c/71bf829800758a6e3889096e4754ef47ba7fc850
- https://git.kernel.org/stable/c/dbf862ce9f009128ab86b234d91413a3e450beb4
- http://www.openwall.com/lists/oss-security/2026/04/28/14
- http://xenbits.xen.org/xsa/advisory-487.html
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