Re: [Clarification] writes to kernel addresses that came from userspace

Hi all!

On 12/09/2021 18:20, Len Baker wrote:
[...]

[extracted from the KSPP]

It should be possible to perform taint tracking of addresses in the kernel
to avoid flaws of the form:

copy_from_user(object, src, ...);
...
memcpy(object.address, something, ...);

[end of extracted]

My question is: Why is this scenario a flaw?

If I understand correctly, the copy_from_user() function copies n bytes of
src (in user space address) to object (in kernel space address). I think > that it is the correct way to act. Then, in kernel space the object is

Yup.

modified. So, I don't see the problem. Sorry if it is a trivial question
but I can not figure it out on my own.

Shouldn't the memcpy() be a copy_to_user() as object.address is setup by 
the user space and thus a user space address?

MfG,
	Bernd
-- 
Bernd Petrovitsch                  Email : bernd@petrovitsch.priv.at
      There is NO CLOUD, just other people's computers. - FSFE
                      LUGA : http://www.luga.at

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