CVE-2026-90078 (GCVE-0-2026-90078)
Vulnerability from cvelistv5
Published
2026-09-17 16:05
Modified
2026-10-19 08:57
Severity ?
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.
References
Impacted products
Vendor Product Version
Linux Linux Version: 56af5e749f20c3a540310c207dcc373f4f09156e
Version: 56af5e749f20c3a540310c207dcc373f4f09156e
Version: 56af5e749f20c3a540310c207dcc373f4f09156e
Version: 56af5e749f20c3a540310c207dcc373f4f09156e
Version: 56af5e749f20c3a540310c207dcc373f4f09156e
Version: 56af5e749f20c3a540310c207dcc373f4f09156e
Version: 56af5e749f20c3a540310c207dcc373f4f09156e
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{
  "containers": {
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          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
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      "cpeApplicability": [
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          "nodes": [
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              "operator": "OR"
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      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet/sched: act_skbmod: fix length calculations and avoid invalid header warnings\n\nsyzbot reported a warning in skb_network_header_len() triggered\nby tcf_skbmod_act():\n\n  !skb_transport_header_was_set(skb)\n  WARNING: CPU: 0 PID: 14949 at include/linux/skbuff.h:3243 skb_network_header_len include/linux/skbuff.h:3243 [inline]\n  WARNING: CPU: 0 PID: 14949 at net/sched/act_skbmod.c:55 tcf_skbmod_act+0xfe8/0x1810 net/sched/act_skbmod.c:55\n\nThere are a few issues in tcf_skbmod_act():\n\n1. Calling skb_network_header_len() assumes skb-\u003etransport_header is set,\n   which is not guaranteed when tcf_skbmod_act() runs at TC ingress.\n2. Unconditionally calling skb_mac_header_len() at the beginning of\n   tcf_skbmod_act() triggers a warning on L3 devices (e.g. TUN) where the\n   MAC header is unset, evaluating to an underflowed garbage length.\n3. On TC ingress, skb-\u003edata points to the network header. Adding the MAC\n   header length to the IP header length causes skb_ensure_writable() to\n   request more bytes than the actual IP packet length, dropping valid\n   short packets (e.g. 28-byte UDP/IPv4 packets).\n\nFix these by:\n- Using skb_network_offset(skb) + sizeof(struct iphdr/ipv6hdr) for\n  SKBMOD_F_ECN so that the required length is correctly calculated on\n  both ingress (offset == 0) and egress (offset == mac_len).\n- Setting max_edit_len to ETH_HLEN for Ethernet header modifications\n  after validating ARPHRD_ETHER."
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-10-19T08:57:34.924Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/985a37781ade19061400100c2ba0f43979dd4d63"
        },
        {
          "url": "https://git.kernel.org/stable/c/d896843d8d925f0adbba319020595cfb1a7bcd57"
        },
        {
          "url": "https://git.kernel.org/stable/c/0675cff3c2924eb9b80d9dd250cf56a1140af157"
        },
        {
          "url": "https://git.kernel.org/stable/c/e8a2027b7e686784a69b2dfcee841d779919f313"
        },
        {
          "url": "https://git.kernel.org/stable/c/1719865b20b22c88d2a55e922eff5ca31b0841f6"
        },
        {
          "url": "https://git.kernel.org/stable/c/62126464f3a6159c0a3dd89e196ba65bfeb0afc6"
        },
        {
          "url": "https://git.kernel.org/stable/c/81d0d1e64f30d9989c829c0953cd6e6c68d9c5fb"
        }
      ],
      "title": "net/sched: act_skbmod: fix length calculations and avoid invalid header warnings",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-90078",
    "datePublished": "2026-09-17T16:05:56.878Z",
    "dateReserved": "2026-09-11T19:38:34.785Z",
    "dateUpdated": "2026-10-19T08:57:34.924Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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