GHSA-845X-Q62G-4V8P
Vulnerability from github – Published: 2026-05-05 18:33 – Updated: 2026-05-08 15:31In the Linux kernel, the following vulnerability has been resolved:
ext4: handle wraparound when searching for blocks for indirect mapped blocks
Commit 4865c768b563 ("ext4: always allocate blocks only from groups inode can use") restricts what blocks will be allocated for indirect block based files to block numbers that fit within 32-bit block numbers.
However, when using a review bot running on the latest Gemini LLM to check this commit when backporting into an LTS based kernel, it raised this concern:
If ac->ac_g_ex.fe_group is >= ngroups (for instance, if the goal group was populated via stream allocation from s_mb_last_groups), then start will be >= ngroups.
Does this allow allocating blocks beyond the 32-bit limit for indirect block mapped files? The commit message mentions that ext4_mb_scan_groups_linear() takes care to not select unsupported groups. However, its loop uses group = *start, and the very first iteration will call ext4_mb_scan_group() with this unsupported group because next_linear_group() is only called at the end of the iteration.
After reviewing the code paths involved and considering the LLM review, I determined that this can happen when there is a file system where some files/directories are extent-mapped and others are indirect-block mapped. To address this, add a safety clamp in ext4_mb_scan_groups().
{
"affected": [],
"aliases": [
"CVE-2026-43067"
],
"database_specific": {
"cwe_ids": [],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-05-05T16:16:15Z",
"severity": "CRITICAL"
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\next4: handle wraparound when searching for blocks for indirect mapped blocks\n\nCommit 4865c768b563 (\"ext4: always allocate blocks only from groups\ninode can use\") restricts what blocks will be allocated for indirect\nblock based files to block numbers that fit within 32-bit block\nnumbers.\n\nHowever, when using a review bot running on the latest Gemini LLM to\ncheck this commit when backporting into an LTS based kernel, it raised\nthis concern:\n\n If ac-\u003eac_g_ex.fe_group is \u003e= ngroups (for instance, if the goal\n group was populated via stream allocation from s_mb_last_groups),\n then start will be \u003e= ngroups.\n\n Does this allow allocating blocks beyond the 32-bit limit for\n indirect block mapped files? The commit message mentions that\n ext4_mb_scan_groups_linear() takes care to not select unsupported\n groups. However, its loop uses group = *start, and the very first\n iteration will call ext4_mb_scan_group() with this unsupported\n group because next_linear_group() is only called at the end of the\n iteration.\n\nAfter reviewing the code paths involved and considering the LLM\nreview, I determined that this can happen when there is a file system\nwhere some files/directories are extent-mapped and others are\nindirect-block mapped. To address this, add a safety clamp in\next4_mb_scan_groups().",
"id": "GHSA-845x-q62g-4v8p",
"modified": "2026-05-08T15:31:15Z",
"published": "2026-05-05T18:33:25Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-43067"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/12624c5b724a81e14e532972b40d863b0de3b7d1"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/2a368ccddfc492a0aa951e2caef2985f20e96503"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/4bec4a498ce86314d470ae6144120461f2138c29"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/83170a05908b6cf2fb3235d3065bf613ff866f3c"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/bb81702370fad22c06ca12b6e1648754dbc37e0f"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/f89bba144938921a2249237ad04a0183ff3f8930"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
"type": "CVSS_V3"
}
]
}
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