On Thu, Aug 25, 2022 at 09:58:46PM +0000, Song Liu wrote: > > > > On Aug 25, 2022, at 12:19 PM, Paul Moore <paul@xxxxxxxxxxxxxx> wrote: > > > > On Thu, Aug 25, 2022 at 2:15 PM Eric W. Biederman <ebiederm@xxxxxxxxxxxx> wrote: > >> Paul Moore <paul@xxxxxxxxxxxxxx> writes: > >>> On Fri, Aug 19, 2022 at 10:45 AM Serge E. Hallyn <serge@xxxxxxxxxx> wrote: > >>>> I am hoping we can come up with > >>>> "something better" to address people's needs, make everyone happy, and > >>>> bring forth world peace. Which would stack just fine with what's here > >>>> for defense in depth. > >>>> > >>>> You may well not be interested in further work, and that's fine. I need > >>>> to set aside a few days to think on this. > >>> > >>> I'm happy to continue the discussion as long as it's constructive; I > >>> think we all are. My gut feeling is that Frederick's approach falls > >>> closest to the sweet spot of "workable without being overly offensive" > >>> (*cough*), but if you've got an additional approach in mind, or an > >>> alternative approach that solves the same use case problems, I think > >>> we'd all love to hear about it. > >> > >> I would love to actually hear the problems people are trying to solve so > >> that we can have a sensible conversation about the trade offs. > > > > Here are several taken from the previous threads, it's surely not a > > complete list, but it should give you a good idea: > > > > https://lore.kernel.org/linux-security-module/CAHC9VhQnPAsmjmKo-e84XDJ1wmaOFkTKPjjztsOa9Yrq+AeAQA@xxxxxxxxxxxxxx/ > > > >> As best I can tell without more information people want to use > >> the creation of a user namespace as a signal that the code is > >> attempting an exploit. > > > > Some use cases are like that, there are several other use cases that > > go beyond this; see all of our previous discussions on this > > topic/patchset. As has been mentioned before, there are use cases > > that require improved observability, access control, or both. > > > >> As such let me propose instead of returning an error code which will let > >> the exploit continue, have the security hook return a bool. With true > >> meaning the code can continue and on false it will trigger using SIGSYS > >> to terminate the program like seccomp does. > > > > Having the kernel forcibly exit the process isn't something that most > > LSMs would likely want. I suppose we could modify the hook/caller so > > that *if* an LSM wanted to return SIGSYS the system would kill the > > process, but I would want that to be something in addition to > > returning an error code like LSMs normally do (e.g. EACCES). > > I am new to user_namespace and security work, so please pardon me if > anything below is very wrong. > > IIUC, user_namespace is a tool that enables trusted userspace code to > control the behavior of untrusted (or less trusted) userspace code. No. user namespaces are not a way for more trusted code to control the behavior of less trusted code. > Failing create_user_ns() doesn't make the system more reliable. > Specifically, we call create_user_ns() via two paths: fork/clone and > unshare. For both paths, we need the userspace to use user_namespace, > and to honor failed create_user_ns(). > > On the other hand, I would echo that killing the process is not > practical in some use cases. Specifically, allowing the application to > run in a less secure environment for a short period of time might be > much better than killing it and taking down the whole service. Of > course, there are other cases that security is more important, and > taking down the whole service is the better choice. > > I guess the ultimate solution is a way to enforce using user_namespace > in the kernel (if it ever makes sense...). But I don't know how that > gonna work. Before we have such solution, maybe we only need an > void hook for observability (or just a tracepoint, coming from BPF > background). > > Thanks, > Song
