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SubjectRe: copy_from_user/copy_to_user question

On Tue, 6 Dec 2005, Vinay Venkataraghavan wrote:

> Thanks to Steve and everybody who sent such detailed
> and timely responses to my question.
> The motivation for the copy to user question is due to
> the handling of ioctl calls in the driver for a chip
> that is widely used. I just could not beleive that
> they would/could commit such a mistake.
> It looks like the old driver code still seems to work
> even without performing copy_to_user and
> copy_from_user.
> But this brings about another scenario. What if the
> case statement in the ioctl call only needs to have
> access to the members of the structure passed in
> through the arg pointer but does not need to modify
> these values and return values.
> Is this still a problem if copy_to_user and
> copy_from_user is not used?
> Thanks,
> Vinay

If you __access__(note) user-mode data from the kernel, you __must__
use the appropriate /copy/to/from/get/put/user functions and/or
macros. And, you __must__ not be in a spin-lock, or otherwise have
the interrupts disabled, while doing it. There are no exceptions.

(note)__assess__ means even "peek at".

FYI, there should never even be such a question.

Dick Johnson
Penguin : Linux version on an i686 machine (5589.55 BogoMips).
Warning : 98.36% of all statistics are fiction.

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