pinctrl: check the return value of pinmux_ops::get_function_name()

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: pinctrl: check the return value of pinmux_ops::get_function_name() While the API contract in docs doesn't specify it explicitly, the generic implementation of the get_function_name() callback from struct pinmux_ops - pinmux_generic_get_function_name() - can fail and return NULL. This is already checked in pinmux_check_ops() so add a similar check in pinmux_func_name_to_selector() instead of passing the returned pointer right down to strcmp() where the NULL can get dereferenced. This is normal operation when adding new pinfunctions.

References

• https://git.kernel.org/stable/c/1a7fc8fed2bb2e113604fde7a45432ace2056b97
• https://git.kernel.org/stable/c/e7265dc4c670b89611bcf5fe33acf99bc0aa294f
• https://git.kernel.org/stable/c/d77ef2f621cd1d605372c4c6ce667c496f6990c3
• https://git.kernel.org/stable/c/ba7f7c2b2b3261e7def67018c38c69b626e0e66e
• https://git.kernel.org/stable/c/1a2ea887a5cd7d47bab599f733d89444df018b1a
• https://git.kernel.org/stable/c/688c688e0bf55824f4a38f8c2180046f089a3e3b
• https://git.kernel.org/stable/c/b7e0535060a60cc99eafc19cc665d979714cd73a
• https://git.kernel.org/stable/c/4002ee98c022d671ecc1e4a84029e9ae7d8a5603