net: gro: properly validate BIG TCP aggregation criteria

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Summary

CVECVE-2026-80725
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-08-29 07:16:54 UTC
Updated2026-08-29 07:16:54 UTC
DescriptionIn the Linux kernel, the following vulnerability has been resolved: net: gro: properly validate BIG TCP aggregation criteria When GRO attempts to aggregate packets beyond GRO_LEGACY_MAX_SIZE (64KB), BIG TCP should only be permitted for plain IPv4 TCP and plain IPv6 TCP (with sufficient MAC header room to insert the temporary HBH jumbo header). However, commit b1a78b9b9886 ("net: add support for ipv4 big tcp") loosened the check in skb_gro_receive(), leading to several issues: 1. skb_gro_receive() checked skb_headroom(p) instead of the actual space before the MAC header (p->mac_header). Because skb_headroom(p) includes mac_len, crafted frames (e.g. injected via AF_PACKET) can pass the check with p->mac_header < 8 bytes. When ipv6_gro_complete() inserts the temporary HBH jumbo header, the memmove() starts before skb->head, causing an out-of-bounds write and wrapping skb->mac_header. 2. It allowed non-IP protocols such as software VLAN (ETH_P_8021Q / ETH_P_8021AD) to aggregate beyond 64KB because p->protocol != ETH_P_IPV6 was true. 3. It checked p->encapsulation instead of NAPI_GRO_CB(skb)->encap_mark, allowing encapsulated flows (e.g. SIT / IPv6-in-IPv4) to aggregate beyond 64KB. Fix skb_gro_receive() to strictly enforce: - NAPI_GRO_CB(skb)->proto == IPPROTO_TCP - Not encapsulated (!NAPI_GRO_CB(skb)->encap_mark && !p->encapsulation) - Protocol must be either ETH_P_IP or ETH_P_IPV6 - If ETH_P_IPV6, p->mac_header must be at least sizeof(struct hop_jumbo_hdr) Returning -E2BIG from skb_gro_receive() ensures that packets which cannot become BIG TCP are cleanly flushed at <= 64KB and delivered intact without dropping. This issue does not exist in mainline (7.0+) because the subsystem was rewritten in commit 81be30c1f5f2 ("net/ipv6: Drop HBH for BIG TCP on RX side"), making this fix relevant only for older stable branches like 6.18.y.

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected 0fe79f28bfaf73b66b7b1562d2468f94aa03bd12 37a5dcd6837fc2afc44a7bc3ed8af4e983783d46 git Not specified
CNA Linux Linux affected 0fe79f28bfaf73b66b7b1562d2468f94aa03bd12 e907bf694ed55bdfe421be99dba35751a655df25 git Not specified
CNA Linux Linux affected 0fe79f28bfaf73b66b7b1562d2468f94aa03bd12 03cb8cc2961f5f781d12e903782cb3815ed84b1c git Not specified
CNA Linux Linux affected 0fe79f28bfaf73b66b7b1562d2468f94aa03bd12 3ce832e2bd431d0c12ba525ed73ad8fbc4191da5 git Not specified
CNA Linux Linux affected 0fe79f28bfaf73b66b7b1562d2468f94aa03bd12 81be30c1f5f2bffda1f04c0efd0746af10b9643a git Not specified
CNA Linux Linux affected 5.19 Not specified
CNA Linux Linux unaffected 5.19 semver Not specified
CNA Linux Linux unaffected 6.1.185 6.1.* semver Not specified
CNA Linux Linux unaffected 6.6.154 6.6.* semver Not specified
CNA Linux Linux unaffected 6.12.106 6.12.* semver Not specified
CNA Linux Linux unaffected 6.18.47 6.18.* semver Not specified
CNA Linux Linux unaffected 7.0 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/03cb8cc2961f5f781d12e903782cb3815ed84b1c 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/e907bf694ed55bdfe421be99dba35751a655df25 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/81be30c1f5f2bffda1f04c0efd0746af10b9643a 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/37a5dcd6837fc2afc44a7bc3ed8af4e983783d46 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/3ce832e2bd431d0c12ba525ed73ad8fbc4191da5 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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