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CVE-2026-90078

net/sched: act_skbmod: fix length calculations and avoid invalid header warnings PUBLISHED

Description (CNA)

In the Linux kernel, the following vulnerability has been resolved: net/sched: act_skbmod: fix length calculations and avoid invalid header warnings syzbot reported a warning in skb_network_header_len() triggered by tcf_skbmod_act(): !skb_transport_header_was_set(skb) WARNING: CPU: 0 PID: 14949 at include/linux/skbuff.h:3243 skb_network_header_len include/linux/skbuff.h:3243 [inline] WARNING: CPU: 0 PID: 14949 at net/sched/act_skbmod.c:55 tcf_skbmod_act+0xfe8/0x1810 net/sched/act_skbmod.c:55 There are a few issues in tcf_skbmod_act(): 1. Calling skb_network_header_len() assumes skb->transport_header is set, which is not guaranteed when tcf_skbmod_act() runs at TC ingress. 2. Unconditionally calling skb_mac_header_len() at the beginning of tcf_skbmod_act() triggers a warning on L3 devices (e.g. TUN) where the MAC header is unset, evaluating to an underflowed garbage length. 3. On TC ingress, skb->data points to the network header. Adding the MAC header length to the IP header length causes skb_ensure_writable() to request more bytes than the actual IP packet length, dropping valid short packets (e.g. 28-byte UDP/IPv4 packets). Fix these by: - Using skb_network_offset(skb) + sizeof(struct iphdr/ipv6hdr) for SKBMOD_F_ECN so that the required length is correctly calculated on both ingress (offset == 0) and egress (offset == mac_len). - Setting max_edit_len to ETH_HLEN for Ethernet header modifications after validating ARPHRD_ETHER.

Affected (CNA)

Vendor / productVersions
Linux / Linuxaffected 56af5e749f20c3a540310c207dcc373f4f09156e before 985a37781ade19061400100c2ba0f43979dd4d63; affected 56af5e749f20c3a540310c207dcc373f4f09156e before d896843d8d925f0adbba319020595cfb1a7bcd57; affected 56af5e749f20c3a540310c207dcc373f4f09156e before 0675cff3c2924eb9b80d9dd250cf56a1140af157; affected 56af5e749f20c3a540310c207dcc373f4f09156e before e8a2027b7e686784a69b2dfcee841d779919f313; affected 56af5e749f20c3a540310c207dcc373f4f09156e before 1719865b20b22c88d2a55e922eff5ca31b0841f6; affected 56af5e749f20c3a540310c207dcc373f4f09156e before 62126464f3a6159c0a3dd89e196ba65bfeb0afc6; affected 56af5e749f20c3a540310c207dcc373f4f09156e before 81d0d1e64f30d9989c829c0953cd6e6c68d9c5fb
Linux / Linuxaffected 5.15; unaffected 0 before 5.15; unaffected 5.15.221 through 5.15.*; unaffected 6.1.188 through 6.1.*; unaffected 6.6.157 through 6.6.*; unaffected 6.12.110 through 6.12.*; unaffected 6.18.52 through 6.18.*; unaffected 7.2.6 through 7.2.*; unaffected 7.3 through *

CWE

No CWE identifiers supplied.

References