Bug 2502411 (CVE-2026-63970)

Summary: CVE-2026-63970 kernel: vsock/virtio: bind uarg before filling zerocopy skb
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
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Priority: high    
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 vsock/virtio transport. This vulnerability occurs when the system processes zerocopy socket buffers (skbs) and encounters an error during memory allocation for fixed-buffer vectored data. The system may attempt to free memory incorrectly, leading to a use-after-free condition or memory corruption. This can potentially allow a local attacker to cause a denial of service or escalate their privileges on the system.
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Description OSIDB Bzimport 2026-07-19 16:06:42 UTC 
In the Linux kernel, the following vulnerability has been resolved:

vsock/virtio: bind uarg before filling zerocopy skb

virtio_transport_send_pkt_info() allocates or reuses the zerocopy uarg
before entering the send loop, but virtio_transport_alloc_skb() still
fills the skb before it inherits that uarg. When fixed-buffer vectored
zerocopy hits MAX_SKB_FRAGS, io_sg_from_iter() may partially attach
managed frags and return -EMSGSIZE. The rollback path call kfree_skb()
to free an skb that carries SKBFL_MANAGED_FRAG_REFS but no uarg, so
skb_release_data() falls through to ordinary frag unref.

Pass the uarg into virtio_transport_alloc_skb() and bind it immediately
before virtio_transport_fill_skb(). This keeps control or no-payload skbs
untouched while ensuring success and rollback share one lifetime rule.
Comment 1 Keith Grant 2026-07-21 23:04:41 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026071959-CVE-2026-63970-1142@gregkh/T