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From: Len Baker <len.baker@gmx.com>
To: "kernelnewbies@kernelnewbies.org"
	<kernelnewbies@kernelnewbies.org>,
	Kees Cook <keescook@chromium.org>
Cc: Len Baker <len.baker@gmx.com>
Subject: [Clarification] writes to kernel addresses that came from userspace
Date: Sun, 12 Sep 2021 18:20:30 +0200	[thread overview]
Message-ID: <20210912162030.GA4692@titan> (raw)

Hi,

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.

[1] https://github.com/KSPP/linux/issues
[2] https://github.com/KSPP/linux/issues/126

Thanks in advance.

Regards,
Len

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             reply	other threads:[~2021-09-12 16:21 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-12 16:20 Len Baker [this message]
2021-09-12 18:22 ` [Clarification] writes to kernel addresses that came from userspace Valentin Vidić
2021-09-12 18:47 ` Kees Cook
2021-09-13  7:59 ` Bernd Petrovitsch
2021-09-13 18:01   ` Kees Cook
2021-09-16  0:59 ` Random Guy
2021-09-18  9:47 ` Len Baker

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