CVE-2026-90078

Summary

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 Software

VendorProductVersion RangeStatus
LinuxLinux56af5e749f20c3a540310c207dcc373f4f09156e < 985a37781ade19061400100c2ba0f43979dd4d63affected
LinuxLinux56af5e749f20c3a540310c207dcc373f4f09156e < d896843d8d925f0adbba319020595cfb1a7bcd57affected
LinuxLinux56af5e749f20c3a540310c207dcc373f4f09156e < 0675cff3c2924eb9b80d9dd250cf56a1140af157affected
LinuxLinux56af5e749f20c3a540310c207dcc373f4f09156e < e8a2027b7e686784a69b2dfcee841d779919f313affected
LinuxLinux56af5e749f20c3a540310c207dcc373f4f09156e < 1719865b20b22c88d2a55e922eff5ca31b0841f6affected
LinuxLinux56af5e749f20c3a540310c207dcc373f4f09156e < 62126464f3a6159c0a3dd89e196ba65bfeb0afc6affected
LinuxLinux56af5e749f20c3a540310c207dcc373f4f09156e < 81d0d1e64f30d9989c829c0953cd6e6c68d9c5fbaffected
LinuxLinux5.15affected
LinuxLinux0 < 5.15unaffected
LinuxLinux5.15.221 <= 5.15.*unaffected
LinuxLinux6.1.188 <= 6.1.*unaffected
LinuxLinux6.6.157 <= 6.6.*unaffected
LinuxLinux6.12.110 <= 6.12.*unaffected
LinuxLinux6.18.52 <= 6.18.*unaffected
LinuxLinux7.2.6 <= 7.2.*unaffected
LinuxLinux7.3-rc1 <= *unaffected

Weaknesses

References