CVE-2026-31787

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

Weakness

The product calls free() twice on the same memory address.

Affected Software

Potential Mitigations

References

• https://git.kernel.org/stable/c/1576ff3869cbd3620717195f971c85b7d7fd62b5
• https://git.kernel.org/stable/c/24daca4fc07f3ff8cd0e3f629cd982187f48436a
• 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