UBUNTU-CVE-2026-45981: Use After Free
In the Linux kernel, the following vulnerability has been resolved: s390/cio: Fix device lifecycle handling in cssallocsubchannel() cssallocsubchannel() calls deviceinitialize() before setting up the DMA masks. If dmasetcoherentmask() or dmasetmask() fails, the error path frees the subchannel structure directly, bypassing the device model reference counting. Once deviceinitialize() has been called, the embedded struct device must be released via putdevice(), allowing the release callback to free the container structure. Fix the error path by dropping the initial device reference with putdevice() instead of calling kfree() directly. This ensures correct device lifetime handling and avoids potential use-after-free or double-free issues.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
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ubuntu/linux-aws-6.8to a version that resolves this vulnerability.Fixed in 6.8.0-1060.63~22.04.1 - Upgrade
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ubuntu/linux-azure-6.8to a version that resolves this vulnerability.Fixed in 6.8.0-1063.71~22.04.1 - Upgrade
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ubuntu/linux-azure-fde-6.8to a version that resolves this vulnerability.Fixed in 6.8.0-1062.69~22.04.1 - Upgrade
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ubuntu/linux-gcp-6.8to a version that resolves this vulnerability.Fixed in 6.8.0-1063.69~22.04.1 - Upgrade
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ubuntu/linux-lowlatency-hwe-6.8to a version that resolves this vulnerability.Fixed in 6.8.0-134.134.1~22.04.1 - Upgrade
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ubuntu/linux-nvidia-6.8to a version that resolves this vulnerability.Fixed in 6.8.0-1058.61~22.04.1 - Upgrade
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ubuntu/linux-aws-fipsto a version that resolves this vulnerability.Fixed in 6.8.0-1060.63+fips1 - Upgrade
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ubuntu/linux-azure-fipsto a version that resolves this vulnerability.Fixed in 6.8.0-1062.69+fips1 - Upgrade
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ubuntu/linux-fipsto a version that resolves this vulnerability.Fixed in 6.8.0-134.134+fips1 - Upgrade
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ubuntu/linux-gcp-fipsto a version that resolves this vulnerability.Fixed in 6.8.0-1063.69+fips1 - Compensating control
In css_alloc_subchannel(), when dma_set_coherent_mask() or dma_set_mask() fails after device_initialize(), release the embedded device with put_device() instead of directly calling kfree() on the subchannel structure.
Event History
Frequently Asked Questions
Which systems are exposed to this issue?
The issue applies to the listed Ubuntu Linux kernel packages, including standard, FIPS, AWS, Azure, and GCP variants. The affected code is in the s390 channel I/O subsystem, so exposure is relevant to systems using that subsystem.
What condition triggers the vulnerable error path?
The error path is reached when DMA mask setup fails after css_alloc_subchannel() has already called device_initialize(). Specifically, dma_set_coherent_mask() or dma_set_mask() must fail.
What can happen if the error path is triggered?
The affected path directly frees a structure whose embedded device has been initialized, bypassing device-model reference counting. This can result in use-after-free or double-free conditions.