Re: [PATCH v3 1/4] seccomp: Add sysctl to display available actions

On Thu, Feb 16, 2017 at 10:47 AM, Tyler Hicks <tyhicks(a)canonical.com&gt; wrote: > On 02/15/2017 09:14 PM, Andy Lutomirski wrote: >> On Mon, Feb 13, 2017 at 7:45 PM, Tyler Hicks <tyhicks(a)canonical.com&gt; wrote: >>> This patch creates a read-only sysctl containing an ordered list of >>> seccomp actions that the kernel supports. The ordering, from left to >>> right, is the lowest action value (kill) to the highest action value >>> (allow). Currently, a read of the sysctl file would return "kill trap >>> errno trace allow". The contents of this sysctl file can be useful for >>> userspace code as well as the system administrator. >> >> Would this make more sense as a new seccomp(2) mode a la >> SECCOMP_HAS_ACTION? Then sandboxy things that have no fs access could >> use it. >> > > It would make sense for code that needs to check which actions are > available. It wouldn't make sense for administrators that need to check > which actions are available unless libseccomp provided a wrapper utility. > > Is this a theoretical concern or do you know of a sandboxed piece of > code that cannot access the sysctl before constructing a seccomp filter? > It's semi-theoretical. But suppose I unshare namespaces, unmount a bunch of stuff, then ask libseccomp to install a filter. (I've written code that does exactly that.) libseccomp won't be able to read the sysctl.

--Andy