ipv6: BUG() in pskb_expand_head() as part of calipso_skbuff_setattr()

{
  "id": "d2e50ec069eebabb6617d8f7d59e43d0a0c547d12225937b265d58560f420d1c",
  "url": "https://osv.dev/vulnerability/CVE-2025-71085",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "ipv6: BUG() in pskb_expand_head() as part of calipso_skbuff_setattr()",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: ipv6: BUG() in pskb_expand_head() as part of calipso_skbuff_setattr() There exists a kernel oops caused by a BUG_ON(nhead < 0) at net/core/skbuff.c:2232 in pskb_expand_head(). This bug is triggered as part of the calipso_skbuff_setattr() routine when skb_cow() is passed headroom > INT_MAX (i.e. (int)(skb_headroom(skb) + len_delta) < 0). The root cause of the bug is due to an implicit integer cast in __skb_cow(). The check (headroom > skb_headroom(skb)) is meant to ensure that delta = headroom - skb_headroom(skb) is never negative, otherwise we will trigger a BUG_ON in pskb_expand_head(). However, if headroom > INT_MAX and delta <= -NET_SKB_PAD, the check passes, delta becomes negative, and pskb_expand_head() is passed a negative value for nhead. Fix the trigger condition in calipso_skbuff_setattr(). Avoid passing \"negative\" headroom sizes to skb_cow() within calipso_skbuff_setattr() by only using skb_cow() to grow headroom. PoC: Using `netlabelctl` tool: netlabelctl map del default netlabelctl calipso add pass doi:7 netlabelctl map add default address:0::1/128 protocol:calipso,7 Then run the following PoC: int fd = socket(AF_INET6, SOCK_DGRAM, IPPROTO_UDP); // setup msghdr int cmsg_size = 2; int cmsg_len = 0x60; struct msghdr msg; struct sockaddr_in6 dest_addr; struct cmsghdr * cmsg = (struct cmsghdr *) calloc(1, sizeof(struct cmsghdr) + cmsg_len); msg.msg_name = &dest_addr; msg.msg_namelen = sizeof(dest_addr",
    "evidence": "osv:CVE-2025-71085",
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    "severity": "high",
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      "modified": "2026-10-28T02:30:22.848733865Z",
      "provider": "osv",
      "references": [
        "https://cert-portal.siemens.com/productcert/html/ssa-019113.html",
        "https://cert-portal.siemens.com/productcert/html/ssa-457936.html",
        "https://git.kernel.org/stable/c/2bb759062efa188ea5d07242a43e5aa5464bbae1",
        "https://git.kernel.org/stable/c/58fc7342b529803d3c221101102fe913df7adb83",
        "https://git.kernel.org/stable/c/6b7522424529556c9cbc15e15e7bd4eeae310910",
        "https://git.kernel.org/stable/c/73744ad5696dce0e0f43872aba8de6a83d6ad570",
        "https://git.kernel.org/stable/c/86f365897068d09418488165a68b23cb5baa37f2",
        "https://git.kernel.org/stable/c/bf3709738d8a8cc6fa275773170c5c29511a0b24",
        "https://git.kernel.org/stable/c/c53aa6a5086f03f19564096ee084a202a8c738c0",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2025/71xxx/CVE-2025-71085.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2025-71085",
        "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"
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    "severity_evidence": "/severity/0/score"
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  "source_id": "core-osv",
  "document_id": 489279,
  "published_at": "2026-01-13T15:34:48.324+00:00"
}