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Date: Fri, 4 Nov 2011 21:04:06 +0400
From: Solar Designer <>
Subject: Re: CVE Request -- kernel: sysctl: restrict write access to dmesg_restrict

Hi Steve,

On Thu, Oct 27, 2011 at 11:38:47PM -0400, Steven M. Christey wrote:
> So, I'll repeat my subtle request in January for someone to try and define 
> what the acceptable security boundaries are at this stage, and then it 
> should make it easier to interpret what needs a CVE (or not).  It sounds 
> like this could have some benefits beyond CVE.  Looks like Brad Spengler's 
> blog post at is a 
> great start; based on my (limited) understanding, this suggests that 
> CAP_SYS_ADMIN can legitimately transition to full root.

What's "full root"?  Full root in the current container or full root on
the host system?

Without container-based virtualization, CAP_SYS_ADMIN is pretty much
equivalent to full root (and I wouldn't ask what that is).

With containers, CAP_SYS_ADMIN inside a container is not supposed to be
equivalent to full root on the host.  Such privilege escalation
possibilities are CVE-worthy.  However, LXC with procfs mounted is
currently an exception.  We can instead have a CVE id for this exception
(not for dmesg_restrict specifically), if desired/appropriate.

With OpenVZ, it is OK to have procfs mounted in a container and not
have a CAP_SYS_ADMIN in container (or other container root access
equivalent) to host root privilege escalation vulnerability (or rather,
such vulnerabilities when found would deserve CVEs of their own).

Since such container-based virtualization for Linux exists where
CAP_SYS_ADMIN is not meant to be equivalent to host root, we should not
disregard CAP_SYS_ADMIN to root privilege escalation bugs in Linux in
general.  Many of these are CVE-worthy.  However, there are occasional
exceptions, such as this case with LXC and procfs where individual
bypasses are not CVE-worthy (but this entire exception might be
CVE-worthy on its own).

I hope this helps.


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