rtc: ac100: Assign .num before accessing .hws

Overview

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.

Affected

• Linux >= f316cdff8d677db9ad9c90acb44c4cd535b0ee27 < 6bb55381daf1a1bed0657189a1396e7467712525
• Linux >= f316cdff8d677db9ad9c90acb44c4cd535b0ee27 < 160619b38707241e22569f9c983a4b3d0890996a
• Linux >= f316cdff8d677db9ad9c90acb44c4cd535b0ee27 < ad1bf77039cba83373bf1eff3784655e3e3ed2ab
• Linux >= f316cdff8d677db9ad9c90acb44c4cd535b0ee27 < 6a4117eee82dd85f11bf898bf66026764011eeb6
• Linux 6.6

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.