On Mon, Sep 13, 2021 at 09:59:36AM +0200, Bernd Petrovitsch wrote:
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?
Right, _correct_ code would pass a userspace address, and use copy_to_user() for writing to it. The goal here would be to find the kinds of paths that might lead to bad conditions (i.e. answering "is it possible for a userspace-controlled value to reach a place in the kernel that didn't sanity-check it before doing indexing, sizing, etc?"). -- Kees Cook