On Tue, Jul 26, 2016 at 8:06 AM, Eric W. Biederman <ebiederm@xxxxxxxxxxxx> wrote: > "Michael Kerrisk (man-pages)" <mtk.manpages@xxxxxxxxx> writes: > >> Hello Eric, >> >> I realized I had a question after the last mail. >> >> On 07/21/2016 06:39 PM, Eric W. Biederman wrote: >>> >>> This patchset addresses two use cases: >>> - Implement a sane upper bound on the number of namespaces. >>> - Provide a way for sandboxes to limit the attack surface from >>> namespaces. >> >> Can you say more about the second point? What exactly is the >> problem that is being addressed, and how does the patch series >> address it? (It would be good to have those details in the >> revised commit message...) > > At some point it was reported that seccomp was not sufficient to disable > namespace creation. I need to go back and look at that claim to see > which set of circumstances that was referring to. Seccomp doesn't stack > so I can see why it is an issue. seccomp does stack. The trouble usually comes from a perception that seccomp overhead is not trivial, so setting a system-wide policy is a bit of a large hammer for such a limitiation. Also, at the time, seccomp could be bypasses with ptrace, but this (as of v4.8) is no longer true. > The general problem is that namespaces by their nature (and especially > in combination with the user namespaces) allow unprivileged users to use > more of the kernel than a user would have access to without them. This > in turn allows malicious users more kernel calls they can use in attempt > to find an exploitable bug. > > So if you are building a sandbox/chroot jail/chromium tab or anything > like that and you know you won't be needing a kernel feature having an > easy way to disable the feature is useful for making the kernel > marginally more secure, as certain attack vectors are no longer > possible. -Kees -- Kees Cook Chrome OS & Brillo Security -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
