[RFC][CFLART] ipmi procfs bogosity

[viro@ZenIV.linux.org.uk]

drivers/char/ipmi/ipmi_poweroff.c::proc_write_chassctrl()
	a) does sscanf on userland pointer
	b) does sscanf on array that is not guaranteed to have NUL in it
	c) interprets input in incredibly cretinous way:
if strings doesn't start with a decimal number => as if it was "0".
if it starts with decimal number equal to 0 (e.g. is "-0000splat") - as if
it was "0".
if it starts with decimal number equal to 2 (e.g. is "00002FOAD") - as if
it was "2".
otherwise - -EINVAL.
	In any case that doesn't end up with -EINVAL, pretend that entire
buffer had been written.

(a) and (b) are immediate bugs; (c) is a valid reason for immediate severe
LARTing of the pervert who had done _that_ in a user-visible API.

Note that API _is_ user-visible, so we can't blindly change it - not without
checking WTF do its users actually write to /proc/ipmi/poweroff_control.

Could somebody comment on the actual uses of that FPOS?  My preference would
be to remove the damn thing completely - it's too ugly to live.