GHSA-4PRH-WFP5-28J7

Vulnerability from github – Published: 2026-10-18 18:31 – Updated: 2026-10-18 18:31
VLAI
Details

In the Linux kernel, the following vulnerability has been resolved:

net: ipv6: keep room for the mac header in dst_dev_overhead()

The seg6, ioam6 and rpl lwtunnels size their skb_cow_head() request as the length they are about to push plus dst_dev_overhead(), then push the new headers and rebuild the mac header below them with skb_mac_header_rebuild(). That rebuild needs skb->mac_len of headroom, but dst_dev_overhead() leaves LL_RESERVED_SPACE() of the egress device, 16 bytes for plain Ethernet.

Where the mac header is longer than that, as it is on ingress through a VLAN device with reorder_hdr off, the rebuild runs out of room: skb_set_mac_header(skb, -skb->mac_len) computes a negative offset, stores it unchecked in the u16 skb->mac_header, and the memmove that follows writes skb->mac_len bytes about 64 KB past skb->head. Forwarding plain ping6 traffic through such a device reproduces it on all five seg6 encapsulation modes and on the rpl and ioam6 inline paths; skb->mac_header comes back as 65534 on a 704-byte head.

Return the larger of the two. The helper already returns skb->mac_len when it has no dst, so this only makes the other branch agree, and it covers every caller rather than each call site in turn.

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{
  "affected": [],
  "aliases": [
    "CVE-2026-98570"
  ],
  "database_specific": {
    "cwe_ids": [],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-10-18T16:17:09Z",
    "severity": null
  },
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet: ipv6: keep room for the mac header in dst_dev_overhead()\n\nThe seg6, ioam6 and rpl lwtunnels size their skb_cow_head() request as\nthe length they are about to push plus dst_dev_overhead(), then push the\nnew headers and rebuild the mac header below them with\nskb_mac_header_rebuild().  That rebuild needs skb-\u003emac_len of headroom,\nbut dst_dev_overhead() leaves LL_RESERVED_SPACE() of the egress device,\n16 bytes for plain Ethernet.\n\nWhere the mac header is longer than that, as it is on ingress through a\nVLAN device with reorder_hdr off, the rebuild runs out of room:\nskb_set_mac_header(skb, -skb-\u003emac_len) computes a negative offset,\nstores it unchecked in the u16 skb-\u003emac_header, and the memmove that\nfollows writes skb-\u003emac_len bytes about 64 KB past skb-\u003ehead.\nForwarding plain ping6 traffic through such a device reproduces it on\nall five seg6 encapsulation modes and on the rpl and ioam6 inline paths;\nskb-\u003emac_header comes back as 65534 on a 704-byte head.\n\nReturn the larger of the two.  The helper already returns skb-\u003emac_len\nwhen it has no dst, so this only makes the other branch agree, and it\ncovers every caller rather than each call site in turn.",
  "id": "GHSA-4prh-wfp5-28j7",
  "modified": "2026-10-18T18:31:54Z",
  "published": "2026-10-18T18:31:54Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-98570"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/36c07127924f11fc5741a780abcaaf808fe9ef13"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/87cd6b717e4069dca34e0866e57eaeb44d3b173e"
    }
  ],
  "schema_version": "1.4.0",
  "severity": []
}



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