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> 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> 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