Bug 2513451 (CVE-2026-68123)

Summary: CVE-2026-68123 kernel: openvswitch: fix GSO userspace truncation underflow
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
Status: NEW --- QA Contact:
Severity: high Docs Contact:
Priority: high    
Version: unspecifiedCC: akhatavk, aos-team-art-private, asdas, dpaolell, jdelft, jupierce, lgarciaa, mbiarnes, ppalepu, ppostler, prdhamdh, rhel-process-autobot, sghai, sidsharm, suppawar, vlaad, watson-tool-maintainers
Target Milestone: ---Keywords: Security
Target Release: ---   
Hardware: All   
OS: Linux   
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A flaw was found in the Open vSwitch component of the Linux kernel. This vulnerability arises from an underflow condition when handling Generic Segmentation Offload (GSO) packets in userspace. A length calculation error can lead to a buffer underflow when data is processed by the `skb_zerocopy()` function. This issue could result in memory corruption, potentially leading to a denial of service or other unpredictable system behavior.
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Description OSIDB Bzimport 2026-08-10 12:38:06 UTC 
In the Linux kernel, the following vulnerability has been resolved:

openvswitch: fix GSO userspace truncation underflow

OVS_ACTION_ATTR_TRUNC currently stores a delta from the original skb
length in OVS_CB(skb)->cutlen. When a later userspace action segments a
GSO skb, queue_gso_packets() reuses that delta for each smaller segment.
A segment can then reach queue_userspace_packet() with cutlen greater
than skb->len, underflowing the length passed to skb_zerocopy().

Store the maximum preserved length instead and bound each consumer
against the current skb length. Use U32_MAX as the no-truncation
sentinel so the value remains valid if skb geometry changes before a
consumer handles it.
Comment 1 Mauro Matteo Cascella 2026-08-11 11:42:22 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026081056-CVE-2026-68123-49d8@gregkh/T