flow_dissector: avoid u16 truncation of skb->len when computing thoff

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-98955
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-10-23 13:17:16 UTC
Updated2026-10-23 13:17:16 UTC
DescriptionIn the Linux kernel, the following vulnerability has been resolved: flow_dissector: avoid u16 truncation of skb->len when computing thoff __skb_flow_dissect() computes key_control->thoff using: key_control->thoff = min_t(u16, nhoff, skb ? skb->len : hlen); min_t(u16, ...) casts both arguments to u16 before comparing them. Whenever skb->len (or hlen) modulo 65536 is smaller than nhoff, the truncated length wins and thoff is set to a bogus small value, even when the dissection succeeded. For example, an IPv4/TCP frame with skb->len == 65540 and nhoff == 34 gets thoff == 4, so callers such as skb_probe_transport_header() point the transport header inside the Ethernet header. Such skbs are not exotic: - At the time of commit d0c081b49137 ("flow_dissector: properly cap thoff field"), AF_PACKET with PACKET_VNET_HDR could already build GSO skbs larger than 64KB (MTU checks are skipped for GSO, and alloc_skb_with_frags() accepted up to MAX_SKB_FRAGS (17) order-0 pages on top of the linear part). - BIG TCP now makes skbs larger than 64KB common. - The following patch makes tun_get_user() dissect IFF_TAP frames before eth_type_trans() pulls the Ethernet header, so a GSO frame carrying a 65522..65535 byte L3 packet will be dissected with skb->len in [65536, 65549]. Compare as u32 instead. If the resulting offset cannot be represented in the u16 key_control->thoff, cap it to U16_MAX and report the dissection as failed rather than silently returning a wrong transport offset. thoff is still set on failure, as some callers (such as eth_get_headlen()) use it regardless of the return value.

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected d0c081b49137cd3200f2023c0875723be66e7ce5 d9e08836d06c84abb18470c94b12b131eaccdc7d git Not specified
CNA Linux Linux affected d0c081b49137cd3200f2023c0875723be66e7ce5 50d0cd575cab763f833d6ac6eb6550b23a0b3dae git Not specified
CNA Linux Linux affected d0c081b49137cd3200f2023c0875723be66e7ce5 9993e6a0ac1b5b3101ffba702cacb9f42b9909d8 git Not specified
CNA Linux Linux affected d0c081b49137cd3200f2023c0875723be66e7ce5 52efce4755a4b8b82039caa773645ffc80b25362 git Not specified
CNA Linux Linux affected d0c081b49137cd3200f2023c0875723be66e7ce5 99bda1ecbd56905f8bd934b9cdccd3bd251192b1 git Not specified
CNA Linux Linux affected d35cd5e279881ec36ff8cd82a2d9caebc0cce3fc git Not specified
CNA Linux Linux affected eecfa2eeefe3caef4c8d6b2284f6066c76ab26a1 git Not specified
CNA Linux Linux affected 80f327285cab6ab8e10c3ea03278add5dd99fb02 git Not specified
CNA Linux Linux affected 4.4.114 4.5 semver Not specified
CNA Linux Linux affected 4.9.79 4.10 semver Not specified
CNA Linux Linux affected 4.14.16 4.15 semver Not specified
CNA Linux Linux affected 4.15 Not specified
CNA Linux Linux unaffected 4.15 semver Not specified
CNA Linux Linux unaffected 6.6.160 6.6.* semver Not specified
CNA Linux Linux unaffected 6.12.113 6.12.* semver Not specified
CNA Linux Linux unaffected 6.18.57 6.18.* semver Not specified
CNA Linux Linux unaffected 7.2.11 7.2.* semver Not specified
CNA Linux Linux unaffected 7.3 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/d9e08836d06c84abb18470c94b12b131eaccdc7d 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/99bda1ecbd56905f8bd934b9cdccd3bd251192b1 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/52efce4755a4b8b82039caa773645ffc80b25362 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/50d0cd575cab763f833d6ac6eb6550b23a0b3dae 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/9993e6a0ac1b5b3101ffba702cacb9f42b9909d8 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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