CVE-2022-49340: ip_gre: test csum_start instead of transport header

Severity: medium (CVSS 5.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2025-02-26 · updated 2026-08-04

Description

In the Linux kernel, the following vulnerability has been resolved: ip_gre: test csum_start instead of transport header GRE with TUNNEL_CSUM will apply local checksum offload on CHECKSUM_PARTIAL packets. ipgre_xmit must validate csum_start after an optional skb_pull, else lco_csum may trigger an overflow. The original check was if (csum && skb_checksum_start(skb) < skb->data) return -EINVAL; This had false positives when skb_checksum_start is undefined: when ip_summed is not CHECKSUM_PARTIAL. A discussed refinement was straightforward if (csum && skb->ip_summed == CHECKSUM_PARTIAL && skb_checksum_start(skb) < skb->data) return -EINVAL; But was eventually revised more thoroughly: - restrict the check to the only branch where needed, in an uncommon GRE path that uses header_ops and calls skb_pull. - test skb_transport_header, which is set along with csum_start in skb_partial_csum_set in the normal header_ops datapath. Turns out skbs can arrive in this branch without the transport header set, e.g., through BPF redirection. Revise the check back to check csum_start directly, and only if CHECKSUM_PARTIAL. Do leave the check in the updated location. Check field regardless of whether TUNNEL_CSUM is configured.

Affected products

Linux kernel: from 4.19.207 before 4.19.247; from 5.4.148 before 5.4.198; from 5.10.68 before 5.10.122; from 5.14.7 before 5.15.47; from 5.16 before 5.17.15; from 5.18 before 5.18.4 — fixed in 4.19.247, 5.10.122, 5.15.47, 5.17.15, 5.18.4, 5.4.198

How to fix

Upgrade to a fixed version: Linux kernel 4.19.247, 5.10.122, 5.15.47, 5.17.15. Check the vendor advisory for mitigations.

References

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