Linux Kernel ac100 RTC: .num uninitialized triggers UBSAN OOB
CVE-2026-98848 Published on October 18, 2026
rtc: ac100: Assign .num before accessing .hws
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.
Products Associated with CVE-2026-98848
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Affected Versions
Linux:- Version f316cdff8d677db9ad9c90acb44c4cd535b0ee27 and below 6bb55381daf1a1bed0657189a1396e7467712525 is affected.
- Version f316cdff8d677db9ad9c90acb44c4cd535b0ee27 and below 160619b38707241e22569f9c983a4b3d0890996a is affected.
- Version f316cdff8d677db9ad9c90acb44c4cd535b0ee27 and below ad1bf77039cba83373bf1eff3784655e3e3ed2ab is affected.
- Version f316cdff8d677db9ad9c90acb44c4cd535b0ee27 and below 6a4117eee82dd85f11bf898bf66026764011eeb6 is affected.
- Version 6.6 is affected.
- Before 6.6 is unaffected.
- Version 6.12.113, <= 6.12.* is unaffected.
- Version 6.18.56, <= 6.18.* is unaffected.
- Version 7.2.10, <= 7.2.* is unaffected.
- Version 7.3-rc6, <= * is unaffected.