GHSA-XJWM-2VHV-89MG

Vulnerability from github – Published: 2026-08-10 15:33 – Updated: 2026-08-10 15:33
VLAI
Details

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

ksmbd: restore DACL size on check_add_overflow() to avoid malformed ACL

check_add_overflow() unconditionally writes the truncated sum into d even on overflow, per its contract in include/linux/overflow.h. The four check_add_overflow() guards in set_posix_acl_entries_dacl() and set_ntacl_dacl() break out of the ACE-building loops on overflow, but the truncated size is then consumed downstream at the end of set_ntacl_dacl():

pndacl->size = cpu_to_le16(le16_to_cpu(pndacl->size) + size);

This produces an on-wire NT ACL whose pndacl->size under-reports the bytes actually written by the preceding fill_ace_for_sid()/memcpy() calls, yielding a malformed ACL that can trigger out-of-bounds reads when re-parsed by clients or ksmbd itself.

Restore size to its pre-addition value on each overflow branch (via *size -= ace_sz / size -= nt_ace_size) so that after the break, size once again holds the cumulative size of the successfully-written ACEs. The committed ACL is then truncated-but-self-consistent rather than malformed.

The ksmbd DACL builders are the only check_add_overflow() sites found where an overflow path breaks out of a loop and the destination value is consumed afterward. The other nearby break-style cases either return -EINVAL on overflow (transport_ipc.c) or break without consuming the overflowed destination value afterward (buildid.c).

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{
  "affected": [],
  "aliases": [
    "CVE-2026-68099"
  ],
  "database_specific": {
    "cwe_ids": [],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-08-10T13:19:54Z",
    "severity": null
  },
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nksmbd: restore DACL size on check_add_overflow() to avoid malformed ACL\n\ncheck_add_overflow() unconditionally writes the truncated sum into *d\neven on overflow, per its contract in include/linux/overflow.h.\nThe four check_add_overflow() guards in set_posix_acl_entries_dacl()\nand set_ntacl_dacl() break out of the ACE-building loops on overflow,\nbut the truncated *size is then consumed downstream at the end of\nset_ntacl_dacl():\n\n    pndacl-\u003esize = cpu_to_le16(le16_to_cpu(pndacl-\u003esize) + size);\n\nThis produces an on-wire NT ACL whose pndacl-\u003esize under-reports the\nbytes actually written by the preceding fill_ace_for_sid()/memcpy()\ncalls, yielding a malformed ACL that can trigger out-of-bounds reads\nwhen re-parsed by clients or ksmbd itself.\n\nRestore *size to its pre-addition value on each overflow branch (via\n`*size -= ace_sz` / `size -= nt_ace_size`) so that after the break,\n*size once again holds the cumulative size of the successfully-written\nACEs. The committed ACL is then truncated-but-self-consistent rather\nthan malformed.\n\nThe ksmbd DACL builders are the only check_add_overflow() sites found\nwhere an overflow path breaks out of a loop and the destination value\nis consumed afterward. The other nearby break-style cases either\nreturn -EINVAL on overflow (transport_ipc.c) or break without\nconsuming the overflowed destination value afterward (buildid.c).",
  "id": "GHSA-xjwm-2vhv-89mg",
  "modified": "2026-08-10T15:33:35Z",
  "published": "2026-08-10T15:33:35Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-68099"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/0bf38372821b1526f31538a7d9811844c55c7f38"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/847ecd4eb3c117c3d2f13f1e7ab506543aad8183"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/bbf0a8e931204ecdab494a88d43b0a24a04285c5"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/bc90144ce8bb7fcf05ad9417c7adb4e9509d9e13"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/f4fcd0c1a243d449307b887fafee23921e9db5ab"
    }
  ],
  "schema_version": "1.4.0",
  "severity": []
}



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