CVE-2026-99057: xen/netfront: don't leak the skb when xennet_fill_frags() fails
In the Linux kernel, the following vulnerability has been resolved:
xen/netfront: don't leak the skb when xennetfillfrags() fails
When a response chain has more slots than fit in the skb's frags, xennetfillfrags() returns an error and xennetpoll() jumps to its error path. That path moves what's left on tmpq to errq to be freed, but the skb being filled was already dequeued from tmpq, so it's never freed. Each chain that overflows leaks the skb and the pages attached to it as frags, and the backend decides how many slots it sends.
Put the skb back on tmpq before taking the error path, like the xennetsetskbgso() failure just above it does.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
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ubuntu/linux-ibmto a version that resolves this vulnerability.Fixed in 7.0.0-1018.18 - Upgrade
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ubuntu/linux-realtimeto a version that resolves this vulnerability.Fixed in 7.0.0-43.43.1 - Compensating control
In xennet_poll(), when xennet_fill_frags() fails, put the skb back on tmpq before taking the error path so it is moved to errq and freed.
Event History
Frequently Asked Questions
What must occur for the leak to be triggered?
A receive response chain must contain more slots than can fit in the skb fragment array, causing xennet_fill_frags() to fail.
Who controls the input that can trigger the condition?
The Xen backend determines how many slots it sends in the response chain. An affected guest is exposed when its netfront driver processes an oversized chain from that backend.
What is the practical impact of repeated triggering?
Each oversized chain can leak the skb that was being filled and the pages attached to it as fragments. Repeated events can therefore consume guest memory.