On Sun, Sep 12, 2021 at 06:20:30PM +0200, Len Baker wrote:
I am taking a look to the issues in the Kernel Self Protection Project [1] and this one [2] (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.
I suppose the problem is that userspace sets the value of object.address to point to something dangerous. If the kernel tries to write to that location later it will cause a crash or worse... -- Valentin