UBUNTU-CVE-2026-74481: Use After Free
In the Linux kernel, the following vulnerability has been resolved: mm/pagereporting: use systemfreezablewq to fix UAF during suspend During PM freeze (e.g. S3 suspend or S4 hibernation), device drivers like virtioballoon reset their underlying virtio devices and delete their virtqueues via vdev->config->delvqs(). However, page reporting work (pagereportingprocess) was scheduled on the global systemwq. Because systemwq lacks the WQFREEZABLE flag, the PM freezer skips it, leaving pagereportingprocess active during suspend. If pages are freed into the buddy allocator while suspending (for example, when core MM invokes the balloon shrinker during S4 hibernation image saving), page reporting triggers virtballoonfreepagereport() on deleted virtqueues, resulting in a Use-After-Free / General Protection Fault: [ 196.795226] general protection fault, probably for non-canonical address 0xaa1436fe70dae6df: 0000 [#1] SMP NOPTI [ 196.825967] Workqueue: events pagereportingprocess [ 196.831038] RIP: 0010:virtqueueaddsplit+0x233/0x4c0 [virtioring] [ 196.927073] virtballoonfreepagereport+0x3a/0xe0 [virtioballoon] [ 196.946943] pagereportingprocess+0x370/0x4f0 Fix this by switching page reporting work to systemfreezablewq. This ensures that the PM freezer pauses pagereportingprocess before device drivers destroy their reporting virtqueues. Because the reporting worker is frozen, memory reclamation/freeing (e.g. via shrinker execution) can safely return pages to MM during freeze without triggering unfrozen reporting work on deleted virtqueues. This aligns with the driver's existing design. The comment in virtballoonfreeze() states: / The workqueue is already frozen by the PM core before this function is called. / Testing: I have verified these fixes using Google’s virtualization infrastructure by running continuous suspend/resume iterations (40+ cycles) while churning memory using stress-ng (stress-ng --vm 4 --vm-bytes 60% --timeout 1) to constantly create free pages for the buddy allocator. We also set the pagereportingorder parameter to 0 to make the page reporting worker highly sensitive, forcing it to pick up any 4K free pages. This confirmed that the UAF crashes are no longer reproducible.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
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ubuntu/linux-aws-5.15to a version that resolves this vulnerability.Fixed in 5.15.0-1117.124~20.04.1 - Upgrade
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ubuntu/linux-azure-5.15to a version that resolves this vulnerability.Fixed in 5.15.0-1123.132~20.04.1 - Upgrade
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ubuntu/linux-azure-fde-5.15to a version that resolves this vulnerability.Fixed in 5.15.0-1122.131~20.04.1 - Upgrade
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ubuntu/linux-gcp-5.15to a version that resolves this vulnerability.Fixed in 5.15.0-1118.128~20.04.1 - Upgrade
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ubuntu/linux-hwe-5.15to a version that resolves this vulnerability.Fixed in 5.15.0-198.208~20.04.1 - Upgrade
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ubuntu/linux-ibm-5.15to a version that resolves this vulnerability.Fixed in 5.15.0-1111.115~20.04.1 - Upgrade
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ubuntu/linux-intel-iotg-5.15to a version that resolves this vulnerability.Fixed in 5.15.0-1112.118~20.04.1 - Upgrade
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ubuntu/linux-lowlatency-hwe-5.15to a version that resolves this vulnerability.Fixed in 5.15.0-195.205~20.04.1 - Upgrade
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ubuntu/linuxto a version that resolves this vulnerability.Fixed in 5.15.0-198.208 - Upgrade
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ubuntu/linux-awsto a version that resolves this vulnerability.Fixed in 5.15.0-1117.124 - Upgrade
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ubuntu/linux-gcpto a version that resolves this vulnerability.Fixed in 5.15.0-1118.128 - Upgrade
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ubuntu/linux-aws-fipsto a version that resolves this vulnerability.Fixed in 5.15.0-1117.124+fips1 - Upgrade
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ubuntu/linux-azure-fipsto a version that resolves this vulnerability.Fixed in 5.15.0-1123.132+fips1 - Upgrade
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ubuntu/linux-fipsto a version that resolves this vulnerability.Fixed in 5.15.0-198.208+fips1 - Upgrade
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ubuntu/linux-gcp-fipsto a version that resolves this vulnerability.Fixed in 5.15.0-1118.128+fips1 - Upgrade
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ubuntu/linux-nvidia-tegrato a version that resolves this vulnerability.Fixed in 6.8.0-1036.39 - Configuration
Switch page reporting work from system_wq to system_freezable_wq so the PM freezer pauses page_reporting_process before virtio drivers destroy their reporting virtqueues.
Linux kernel mm/page_reporting page reporting workqueue = system_freezable_wq - Configuration
Set the page_reporting_order parameter to 0 so the page reporting worker picks up 4K free pages.
Linux kernel mm/page_reporting page_reporting_order = 0
Event History
Frequently Asked Questions
Which systems are most likely to encounter this issue?
Systems using the listed Ubuntu kernel packages that use virtio ballooning and page reporting are implicated. The failure occurs during PM freeze, including S3 suspend or S4 hibernation, when virtio devices are reset and their virtqueues are deleted.
What conditions lead to the use-after-free?
Page-reporting work must remain active while suspend is in progress, and pages must be returned to the buddy allocator. One cited trigger is the core memory manager invoking the balloon shrinker while saving an S4 hibernation image.
How can I identify an affected failure in logs?
The reported failure is a general protection fault or use-after-free involving virtqueue_add_split, virtballoon_free_page_report, and page_reporting_process. The workqueue context may appear as "Workqueue: events page_reporting_process".