Re: [PATCH] serial: 8250: Disallow runtime changes to nr_uarts

[sashiko-bot@kernel.org]

> nr_uarts is clamped to UART_NR while the initial 8250 ports are
> initialized, but it is also used as the iteration bound by the remove
> path. serial8250_get_port() assumes that the index is within the
> serial8250_ports array.
> 
> Allowing nr_uarts to be changed through sysfs can therefore make the
> remove path access beyond the end of serial8250_ports. The value also
> describes the number of initialized or dynamically registered ports, so
> changing it after setup is not safe even when the new value is within the
> array limit.
> 
> Make the nr_uarts module parameter read-only through sysfs. Boot-time and
> module-load parameter parsing remain supported and still go through the
> existing clamp.
> 
> Tested on x86-64 with CONFIG_KASAN=y under QEMU:
> - 8250.nr_uarts=5 is honored at boot.
> - Writes to /sys/module/8250/parameters/nr_uarts are rejected.
> 
> Signed-off-by: Yingjie Wang <1075151112@qq.com>

Sashiko has reviewed this patch and found no issues.

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