On Monday, 25 May 2020 09:37:19 PDT Ed Maste wrote: > On Sat, 16 May 2020 at 20:02, Ihor Antonov <ihor@antonovs.family> wrote: > > Hello FreeBSD Community, > > > > I am looking for possible options to sandbox an untrusted application that > > runs with root privileges. > > > > I can't use Jails or Capsicum as modification of the application is > > outside of the scope of my task and application needs to share the file > > system with some other applications. (several applications use PAM to > > authenticate users and they all have to have the same set of users, and I > > want > > to avoid duplicating system users across jails) > > > > For this write up I will use opensmptd server as an example application, > > but there are many more examples that fit the usecase. > > Is the application dynamically linked? If so it's possible to do > "oblivious sandboxing" with Capsicum. There's a proof of concept in > the "Super Capsicumizer 9000" - > https://github.com/myfreeweb/capsicumizer. It builds on libpreopen > from MUN which handles filesystem access. This is not something that > will work "out of the box" today for your application, but is an area > of active interest that could benefit from a motivating use case. With > some development work (using the approach of capsicumizer + > libpreopen) it could be the basis for a quality sandbox. > > > 1) Application should only be able to listen and talk to TCP port 25. > > > > Initiating connections to other TCP ports and other address families > > must be prevented. > > This would be net new work, intercepting connect(2), accept(2) and > such, passing the args to a socket service, and returning the fd. > > > 2) Application should only have write access to a specific directory, the > > > > rest of the filesystem must be seen by the application as read-only. > > Capsicumizer + libpreopen is most of the way there now. A little work > would be needed to extend it to support different permissions per > directory group. > > > 3) Application should not be able to change it's login class. > > This is inherent in capability mode. > > > 4) Application should not be able to escape the sandbox by forking a child > > > > process. > > Capsicum does not address this, but the child starts in capability > mode and inherits the same sandbox restrictions. The real need then is > for comprehensive resource limits. > > > 5) Application's resource usage must be limited. > > > > 6) Application should not be able to shake-off resource limits by forking > > > > a child or changing login class. > > This probably needs some rctl improvements. > > > 7) Application should not be able to change system configuration, > > load/unload> > > kernel modules, modify firewall rules. > > > > 8) Application should not be able to create new system users, > > > > or change passwords of existing users > > These are inherent in capability mode.
Thanks Ed, I was looking at Capsicumizer and it looks very interesting. The only reason I was hesitant is that this is an external application, not a FreeBSD core. Is it going to be included in FreeBSD in some distant future? -- Ihor Antonov
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