NuytsTech Security

CVE-2026-31787

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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

More information : https://git.kernel.org/stable/c/1576ff3869cbd3620717195f971c85b7d7fd62b5

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