rtc: mpfs: fix unchecked devm_clk_get() error pointer in probe()

Overview

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

rtc: mpfs: fix unchecked devm_clk_get() error pointer in probe()

devm_clk_get(&pdev->dev, "rtcref")'s return value was passed straight into clk_get_rate() without checking it for an error first, unlike the "rtc" clock a few lines above which is correctly checked with IS_ERR(). clk_get_rate() only guards against a NULL clk, not an error pointer:

if (!clk)
	return 0;
...
rate = clk_core_get_rate_recalc(clk->core);

so if devm_clk_get() ever returns an error pointer here (for example ERR_PTR(-EPROBE_DEFER), which is the normal, expected outcome if the clkcfg clock-provider this RTC depends on has not registered its clocks yet by the time this driver probes), clk_get_rate() dereferences that error pointer instead of returning 0, crashing instead of letting probe defer.

Capture the clock in the existing 'clk' local and check it with IS_ERR() before calling clk_get_rate(), matching the handling already used for the "rtc" clock in this same function.

Affected

• Linux >= 0b31d703598dc1993867597bbd45e87d824fc427 < 74dc7c52946e3d47c40edd0875adb7cc15937066
• Linux >= 0b31d703598dc1993867597bbd45e87d824fc427 < cfd70c9b19846c524f2b6195a7484bdf22071ccf
• Linux >= 0b31d703598dc1993867597bbd45e87d824fc427 < 8a03f8422fa08eed335c51bccb612a3d81739ff2
• Linux >= 0b31d703598dc1993867597bbd45e87d824fc427 < ac41b05d15db3134e839148290d67415ee0bdb58
• Linux 6.0

Remediation

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