Bug 2482057 (CVE-2026-45890)

Summary: CVE-2026-45890 kernel: xen-netback: reject zero-queue configuration from guest
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
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Version: unspecifiedCC: rhel-process-autobot, watson-tool-maintainers
Target Milestone: ---Keywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in the Linux kernel's xen-netback component. A malicious or buggy Xen guest can exploit this by writing a zero value to the 'multi-queue-num-queues' xenbus key. This improper input validation can trigger a warning in the kernel's memory allocation, leading to a guest-to-host Denial of Service (DoS) on systems configured to panic on warnings.
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Description OSIDB Bzimport 2026-05-27 15:09:14 UTC 
In the Linux kernel, the following vulnerability has been resolved:

xen-netback: reject zero-queue configuration from guest

A malicious or buggy Xen guest can write "0" to the xenbus key
"multi-queue-num-queues". The connect() function in the backend only
validates the upper bound (requested_num_queues > xenvif_max_queues)
but not zero, allowing requested_num_queues=0 to reach
vzalloc(array_size(0, sizeof(struct xenvif_queue))), which triggers
WARN_ON_ONCE(!size) in __vmalloc_node_range().

On systems with panic_on_warn=1, this allows a guest-to-host denial
of service.

The Xen network interface specification requires
the queue count to be "greater than zero".

Add a zero check to match the validation already present
in xen-blkback, which has included this
guard since its multi-queue support was added.
Comment 1 Keith Grant 2026-05-28 02:55:00 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026052717-CVE-2026-45890-a18a@gregkh/T