GHSA-35Q6-8FHF-PG65
Vulnerability from github – Published: 2026-09-25 12:31 – Updated: 2026-09-25 15:31In the Linux kernel, the following vulnerability has been resolved:
ufs: validate cylinder group metadata before caching it
ufs_read_cylinder() copies the cylinder group index and the rotor positions straight from the on-disk group and caches them without any check:
ucpi->c_cgx = fs32_to_cpu(sb, ucg->cg_cgx);
ucpi->c_rotor = fs32_to_cpu(sb, ucg->cg_rotor);
ucpi->c_frotor = fs32_to_cpu(sb, ucg->cg_frotor);
ucpi->c_irotor = fs32_to_cpu(sb, ucg->cg_irotor);
They are then used as indices during allocation and free:
-
c_cgx indexes the cylinder summary array as UFS_SB(sb)->fs_cs(ucpi->c_cgx), so a value past s_ncg writes a 32 bit count outside the s_csp allocation.
-
c_frotor becomes a bitmap scan start, start = c_frotor >> 3, and then length = ((s_fpg + 7) >> 3) - start. A start beyond the block bitmap wraps the unsigned length to a huge value, so ubh_scanc() walks far past the cylinder group buffers. c_irotor drives the inode bitmap the same way.
A crafted image can set any of these freely, turning an ordinary allocation into an out of bounds access.
Reject a cylinder group whose recorded index does not match the group being read, or whose rotors fall outside the group, before the metadata is cached. Valid filesystems keep cg_cgx equal to the group number and the rotors within the group, so only malformed images are rejected.
{
"affected": [],
"aliases": [
"CVE-2026-97926"
],
"database_specific": {
"cwe_ids": [],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-09-25T11:17:19Z",
"severity": "HIGH"
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\nufs: validate cylinder group metadata before caching it\n\nufs_read_cylinder() copies the cylinder group index and the rotor\npositions straight from the on-disk group and caches them without any\ncheck:\n\n\tucpi-\u003ec_cgx = fs32_to_cpu(sb, ucg-\u003ecg_cgx);\n\tucpi-\u003ec_rotor = fs32_to_cpu(sb, ucg-\u003ecg_rotor);\n\tucpi-\u003ec_frotor = fs32_to_cpu(sb, ucg-\u003ecg_frotor);\n\tucpi-\u003ec_irotor = fs32_to_cpu(sb, ucg-\u003ecg_irotor);\n\nThey are then used as indices during allocation and free:\n\n - c_cgx indexes the cylinder summary array as\n UFS_SB(sb)-\u003efs_cs(ucpi-\u003ec_cgx), so a value past s_ncg writes a 32\n bit count outside the s_csp allocation.\n\n - c_frotor becomes a bitmap scan start, start = c_frotor \u003e\u003e 3, and\n then length = ((s_fpg + 7) \u003e\u003e 3) - start. A start beyond the block\n bitmap wraps the unsigned length to a huge value, so ubh_scanc()\n walks far past the cylinder group buffers. c_irotor drives the\n inode bitmap the same way.\n\nA crafted image can set any of these freely, turning an ordinary\nallocation into an out of bounds access.\n\nReject a cylinder group whose recorded index does not match the group\nbeing read, or whose rotors fall outside the group, before the metadata\nis cached. Valid filesystems keep cg_cgx equal to the group number and\nthe rotors within the group, so only malformed images are rejected.",
"id": "GHSA-35q6-8fhf-pg65",
"modified": "2026-09-25T15:31:44Z",
"published": "2026-09-25T12:31:28Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-97926"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/5902a95066883cf96fa15b2680694fc5dd0c7d11"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/87b12dc360a002eb2d498aa4f01e84347019612d"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/abde9eb33106850dfa367ad3965d3588bb8558d5"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/c9d263be26806d388129fab8c6904bed197fc6af"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:L/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H",
"type": "CVSS_V3"
}
]
}
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