GHSA-P997-JC38-XXH3
Vulnerability from github – Published: 2026-09-17 18:31 – Updated: 2026-09-17 18:31In the Linux kernel, the following vulnerability has been resolved:
lwt_bpf: Restore reserved headroom after xmit program
ip_finish_output2() expands an skb to LL_RESERVED_SPACE(dev) before LWT xmit. An LWT_XMIT BPF program can then modify the skb head and still return BPF_OK, so bpf_xmit() rechecks the remaining headroom before the skb continues to neighbour output.
That recheck uses dst->dev->hard_header_len. This is not enough for the neighbour cached-header path: neigh_hh_output() copies the cached hardware header using the aligned hh_cache size, HH_DATA_MOD for short headers or HH_DATA_ALIGN(hh_len) otherwise.
On Ethernet, hard_header_len is 14 but the cached copy needs 16 bytes. If an LWT_XMIT BPF program calls bpf_skb_change_head(skb, 1, 0), the skb can still have 15 bytes of headroom after the program. The existing check accepts that, after which neigh_hh_output() hits its headroom warning and drops the skb.
Use LL_RESERVED_SPACE(dst->dev) in the post-BPF headroom check to match the reservation made before LWT xmit.
{
"affected": [],
"aliases": [
"CVE-2026-90160"
],
"database_specific": {
"cwe_ids": [],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-09-17T17:17:09Z",
"severity": null
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\nlwt_bpf: Restore reserved headroom after xmit program\n\nip_finish_output2() expands an skb to LL_RESERVED_SPACE(dev) before LWT\nxmit. An LWT_XMIT BPF program can then modify the skb head and still\nreturn BPF_OK, so bpf_xmit() rechecks the remaining headroom before the\nskb continues to neighbour output.\n\nThat recheck uses dst-\u003edev-\u003ehard_header_len. This is not enough for the\nneighbour cached-header path: neigh_hh_output() copies the cached hardware\nheader using the aligned hh_cache size, HH_DATA_MOD for short headers or\nHH_DATA_ALIGN(hh_len) otherwise.\n\nOn Ethernet, hard_header_len is 14 but the cached copy needs 16 bytes. If\nan LWT_XMIT BPF program calls bpf_skb_change_head(skb, 1, 0), the skb can\nstill have 15 bytes of headroom after the program. The existing check\naccepts that, after which neigh_hh_output() hits its headroom warning and\ndrops the skb.\n\nUse LL_RESERVED_SPACE(dst-\u003edev) in the post-BPF headroom check to match\nthe reservation made before LWT xmit.",
"id": "GHSA-p997-jc38-xxh3",
"modified": "2026-09-17T18:31:53Z",
"published": "2026-09-17T18:31:53Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-90160"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/179a5b2171573d94a25c9aa8e1c9f9ac352ad316"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/5fe7007aed9ad069b2bd77e5d0c875c64f5c0269"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/753e5cdcca5474d230d62bb3489e5168ab27c272"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/7cf561843ed0ad57501892a65abb77957e6c800f"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/7d043e24520a273c362be5dd7d9c82796879a49b"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/a38c0eb447e2dd0120a2ebcdba470f9505ac8907"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/c488071c3441fa34f5a87cd6c12ce2cc6304f20e"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/de2b2004e16f2930eb689175e2c1998b0a68d499"
}
],
"schema_version": "1.4.0",
"severity": []
}
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