Bug 2486449 (CVE-2026-46280)

Summary: CVE-2026-46280 kernel: lib: test_hmm: evict device pages on file close to avoid use-after-free
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
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Priority: medium    
Version: unspecifiedCC: rhel-process-autobot, watson-tool-maintainers
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OS: Linux   
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A flaw was found in the Linux kernel's Heterogeneous Memory Management (HMM) test module. When a device mirror (dmirror) structure is freed, its associated device private pages are not properly migrated back to system memory. This can lead to a use-after-free condition where a dangling pointer to the freed dmirror is dereferenced, potentially causing a kernel panic. A local attacker could exploit this to trigger a denial of service.
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Description OSIDB Bzimport 2026-06-08 17:02:30 UTC 
In the Linux kernel, the following vulnerability has been resolved:

lib: test_hmm: evict device pages on file close to avoid use-after-free

Patch series "Minor hmm_test fixes and cleanups".

Two bugfixes a cleanup for the HMM kernel selftests.  These were mostly
reported by Zenghui Yu with special thanks to Lorenzo for analysing and
pointing out the problems.


This patch (of 3):

When dmirror_fops_release() is called it frees the dmirror struct but
doesn't migrate device private pages back to system memory first.  This
leaves those pages with a dangling zone_device_data pointer to the freed
dmirror.

If a subsequent fault occurs on those pages (eg.  during coredump) the
dmirror_devmem_fault() callback dereferences the stale pointer causing a
kernel panic.  This was reported [1] when running mm/ksft_hmm.sh on arm64,
where a test failure triggered SIGABRT and the resulting coredump walked
the VMAs faulting in the stale device private pages.

Fix this by calling dmirror_device_evict_chunk() for each devmem chunk in
dmirror_fops_release() to migrate all device private pages back to system
memory before freeing the dmirror struct.  The function is moved earlier
in the file to avoid a forward declaration.
Comment 1 Keith Grant 2026-06-08 19:59:54 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026060841-CVE-2026-46280-13e3@gregkh/T