Correct incantation to get a string in sys_security?

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dwheelerat_private

Hi folks - I need some quick help.
What's the proper incantation to use in sys_security()
to acquire a string sent from userspace
as the first parameter of "args"?

As you know, sys_security has this form:
static int stacker_sys_security (unsigned int id, unsigned int call,
                                unsigned long *args)

I check for the correct id, then check for certain call values,
and for certain call values I need the user to pass in a
C string (\0-terminated, with a maximum size).
get_user() seems to be for single characters, so that's not
what I want.

Preprocessor-defined copy_from_user() takes a constant length,
which isn't really what I want. I guess that could do if necessary,
though I'd prefer to stop copying on \0 (to avoid funky problems if
there isn't valid memory if I do a full copy).
The documentation on copy_from_user is pitiful;
I'm not sure what I can trust and I'm not sure what
incantations are necessary to use it to get the string I need.

Suggestions welcome!  I suspect for somebody here, this is an
easy question.

--- David A. Wheeler

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