[Clarification] writes to kernel addresses that came from userspace
len.baker at gmx.com
Sun Sep 12 12:20:30 EDT 2021
I am taking a look to the issues in the Kernel Self Protection Project 
and this one  (perform taint-tracking of writes to kernel addresses
that came from userspace) take my attention. Reading the explanation does
not make it clear to me where the flaw is.
[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
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.
Thanks in advance.
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