CVE-2023-53854

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

ASoC: mediatek: mt8186: Fix use-after-free in driver remove path

When devm runs function in the "remove" path for a device it runs them in the reverse order. That means that if you have parts of your driver that aren't using devm or are using "roll your own" devm w/ devmaddactionorreset() you need to keep that in mind.

The mt8186 audio driver didn't quite get this right. Specifically, in mt8186initclock() it called mt8186audsysclkregister() and then went on to call a bunch of other devm function. The caller of mt8186initclock() used devmaddactionorreset() to call mt8186deinit_clock() but, because of the intervening devm functions, the order was wrong.

Specifically at probe time, the order was: 1. mt8186audsysclkregister() 2. afepriv->clk = devmkcalloc(...) 3. afepriv->clk[i] = devmclkget(...)

At remove time, the order (which should have been 3, 2, 1) was: 1. mt8186audsysclkunregister() 3. Free all of afepriv->clk[i] 2. Free afe_priv->clk

The above seemed to be causing a use-after-free. Luckily, it's easy to fix this by simply using devm more correctly. Let's move the devmaddactionorreset() to the right place. In addition to fixing the use-after-free, code inspection shows that this fixes a leak (missing call to mt8186audsysclkunregister()) that would have happened if any of the sysconregmaplookupbyphandle() calls in mt8186init_clock() had failed.