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 arent using devm or are using roll your own devm w/ devm_add_action_or_reset() you need to keep that in mind.

The mt8186 audio driver didnt quite get this right. Specifically, in mt8186_init_clock() it called mt8186_audsys_clk_register() and then went on to call a bunch of other devm function. The caller of mt8186_init_clock() used devm_add_action_or_reset() to call mt8186_deinit_clock() but, because of the intervening devm functions, the order was wrong.

Specifically at probe time, the order was:

1. mt8186_audsys_clk_register()
2. afe_priv->clk = devm_kcalloc(…)
3. afe_priv->clk[i] = devm_clk_get(…)

At remove time, the order (which should have been 3, 2, 1) was:

1. mt8186_audsys_clk_unregister()
2. Free all of afe_priv->clk[i]
3. Free afe_priv->clk

The above seemed to be causing a use-after-free. Luckily, its easy to fix this by simply using devm more correctly. Lets move the devm_add_action_or_reset() to the right place. In addition to fixing the use-after-free, code inspection shows that this fixes a leak (missing call to mt8186_audsys_clk_unregister()) that would have happened if any of the syscon_regmap_lookup_by_phandle() calls in mt8186_init_clock() had failed.

Affected Software

References

• https://git.kernel.org/stable/c/3e56a1c04882852e3e7d6c59756a16211ebbc457
• https://git.kernel.org/stable/c/a93d2afd3f77a7331271a0f25c6a11003db69b3c
• https://git.kernel.org/stable/c/dffd9e2b57cb845930fa885aa634a847ba2130dd