GHSA-V583-2W7F-R9GC

Vulnerability from github – Published: 2026-09-25 12:31 – Updated: 2026-09-25 12:31
VLAI
Details

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

tracing: Free histogram the field rejected for a bad modifier

Writing a hist trigger whose value or variable carries a modifier that is not allowed there leaks the fields that were built for it.

__create_val_field() takes the field from parse_expr() and stores it in hist_data->fields[] only after the modifier checks have run:

hist_field = parse_expr(hist_data, file, field_str, flags, var_name,
            &n_subexprs);
...
if (hist_field->flags & HIST_FIELD_FL_VAR) {
    if (hist_field->flags & (...))
        goto err;
} else {
    if (hist_field->flags & (...))
        goto err;
}

hist_data->fields[val_idx] = hist_field;

Both checks jump past that store, and the err label returns without freeing anything. The error unwinds to create_hist_data(), which calls destroy_hist_data() -> destroy_hist_fields(), and that reaches a field only by walking fields[]. A field that never got there is unreachable.

commit e0213434fe3e ("tracing: Do not let histogram values have some modifiers") set ret to -EINVAL and fell through to the store, which left the field owned by fields[] and freed along with the rest of hist_data. Splitting the check into a value case and a variable case replaced that fall-through with a goto that skips it.

With CONFIG_DEBUG_KMEMLEAK, 200 writes of

# echo 'hist:keys=prev_pid:vals=next_pid.log2' > \ events/sched/sched_switch/trigger

each correctly rejected with -EINVAL, leave 332 unreferenced objects (63744 bytes) reported at create_hist_field(); 200 install and remove cycles of a valid trigger leave none. A '.log2' field is two allocations, since create_hist_field() puts the plain field in operands[0] of the log2 field, and both are reported.

Use destroy_hist_field() rather than __destroy_hist_field() so that operands[0] is freed as well. It returns early for HIST_FIELD_FL_VAR_REF, which is what an operand owned by hist_data->var_refs[] needs; the rejected field itself is never a var ref, because a var ref never carries a modifier flag.

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{
  "affected": [],
  "aliases": [
    "CVE-2026-97921"
  ],
  "database_specific": {
    "cwe_ids": [],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-09-25T11:17:19Z",
    "severity": null
  },
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\ntracing: Free histogram the field rejected for a bad modifier\n\nWriting a hist trigger whose value or variable carries a modifier that is\nnot allowed there leaks the fields that were built for it.\n\n__create_val_field() takes the field from parse_expr() and stores it in\nhist_data-\u003efields[] only after the modifier checks have run:\n\n\thist_field = parse_expr(hist_data, file, field_str, flags, var_name,\n\t\t\t\t\u0026n_subexprs);\n\t...\n\tif (hist_field-\u003eflags \u0026 HIST_FIELD_FL_VAR) {\n\t\tif (hist_field-\u003eflags \u0026 (...))\n\t\t\tgoto err;\n\t} else {\n\t\tif (hist_field-\u003eflags \u0026 (...))\n\t\t\tgoto err;\n\t}\n\n\thist_data-\u003efields[val_idx] = hist_field;\n\nBoth checks jump past that store, and the err label returns without\nfreeing anything. The error unwinds to create_hist_data(), which calls\ndestroy_hist_data() -\u003e destroy_hist_fields(), and that reaches a field\nonly by walking fields[]. A field that never got there is unreachable.\n\ncommit e0213434fe3e (\"tracing: Do not let histogram values have some\nmodifiers\") set ret to -EINVAL and fell through to the store, which left\nthe field owned by fields[] and freed along with the rest of hist_data.\nSplitting the check into a value case and a variable case replaced that\nfall-through with a goto that skips it.\n\nWith CONFIG_DEBUG_KMEMLEAK, 200 writes of\n\n  # echo \u0027hist:keys=prev_pid:vals=next_pid.log2\u0027 \u003e \\\n\t events/sched/sched_switch/trigger\n\neach correctly rejected with -EINVAL, leave 332 unreferenced objects\n(63744 bytes) reported at create_hist_field(); 200 install and remove\ncycles of a valid trigger leave none. A \u0027.log2\u0027 field is two\nallocations, since create_hist_field() puts the plain field in\noperands[0] of the log2 field, and both are reported.\n\nUse destroy_hist_field() rather than __destroy_hist_field() so that\noperands[0] is freed as well. It returns early for HIST_FIELD_FL_VAR_REF,\nwhich is what an operand owned by hist_data-\u003evar_refs[] needs; the\nrejected field itself is never a var ref, because a var ref never carries\na modifier flag.",
  "id": "GHSA-v583-2w7f-r9gc",
  "modified": "2026-09-25T12:31:28Z",
  "published": "2026-09-25T12:31:28Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-97921"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/230234d12ce42ab04132a32c3a848f07a5d27a71"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/891c21f6d5673b2a519b536243bfc6dd2d35beb6"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/b22dc0add7d72b8bd9cae3188db0dd65da1c8652"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/e787361bb6b0026ea3eb4d3fa7a304c7fcb99555"
    }
  ],
  "schema_version": "1.4.0",
  "severity": []
}



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