On Tue, May 26, 2020 at 08:59:29AM -0500, Eric W. Biederman wrote: > Adrian Reber <areber@xxxxxxxxxx> writes: > > > On Fri, May 22, 2020 at 09:40:37AM -0700, Casey Schaufler wrote: > > >> What are the other blockers? Are you going to suggest additional new > >> capabilities to clear them? > > > > As mentioned somewhere else access to /proc/<pid>/map_files/ would be > > helpful. Right now I am testing with a JVM and it works without root > > just with the attached patch. Without access to /proc/<pid>/map_files/ > > not everything CRIU can do will actually work, but we are a lot closer > > to what our users have been asking for. > > The current permission checks on /proc/<pid>/map_files/ are simply > someone being over-cautious. > > Someone needs to think through the threat landscape and figure out what > permission checks are actually needed. > > Making the permission check ns_capable instead of capable is a > no-brainer. Figuring out which user_ns to test against might be a > we bit harder. > > We could probably even allow the owner of the process to open the files > but that requires someone doing the work of thinking through how > being able to opening files that you have mmaped might be a problem. As mentioned in the other thread, CRIU can work with read access to map_files. > >> > There are probably a few more things guarded by CAP_SYS_ADMIN required > >> > to run checkpoint/restore as non-root, > >> > >> If you need CAP_SYS_ADMIN anyway you're not gaining anything by > >> separating out CAP_RESTORE. > > > > No, as described we can checkpoint and restore a JVM with this patch and > > it also solves the problem the set_ns_last_pid fork() loop daemon tries > > to solve. It is not enough to support the full functionality of CRIU as > > map_files is also important, but we do not need CAP_SYS_ADMIN and > > CAP_RESTORE. Only CAP_RESTORE would be necessary. > > > > With a new capability users can enable checkpoint/restore as non-root > > without giving CRIU access to any of the other possibilities offered by > > CAP_SYS_ADMIN. Setting a PID and map_files have been introduced for CRIU > > and used to live behind CONFIG_CHECKPOINT_RESTORE. Having a capability > > for checkpoint/restore would make it easier for CRIU users to run it as > > non-root and make it very clear what is possible when giving CRIU the > > new capability. No other things would be allowed than necessary for > > checkpoint/restore. Setting a PID is most important for the restore part > > and reading map_files would be helpful during checkpoint. So it actually > > should be called CAP_CHECKPOINT_RESTORE as Christian mentioned in > > another email. > > Please if one is for checkpoint and one is for restore asking for a pair > of capabilities is probably more appropriate. I will send out a v2 with a renamed capability soon and also include map_files to be readable with that capability. > >> > but by applying this patch I can > >> > already checkpoint and restore processes as non-root. As there are > >> > already multiple workarounds I would prefer to do it correctly in the > >> > kernel to avoid that CRIU users are starting to invent more workarounds. > >> > >> You've presented a couple of really inappropriate implementations > >> that would qualify as workarounds. But the other two are completely > >> appropriate within the system security policy. They don't "get around" > >> the problem, they use existing mechanisms as they are intended. > > > > I agree with the user namespace approach to be appropriate, but not the > > CAP_SYS_ADMIN approach as CRIU only needs a tiny subset (2 things) of > > what CAP_SYS_ADMIN allows. > > > If we are only talking 2 things can you please include in your patchset > a patch enabling those 2 things? The two things are setting a PID via ns_last_pid/clone3() and reading map_files. > But even more than this we need a request that asks not for the least > you can possibly ask for but asks for what you need to do a good job. Also in this thread Kamil mentioned that they also need calling prctl with PR_SET_MM during restore in their production setup. > I am having visions of a recurring discussion that says can we add one > more permission check to CAP_RESTORE or CAP_CHECKPOINT when they are > things we could know today. I will prepare a new version of this patch using CAP_CHECKPOINT_RESTORE for ns_last_pid/clone3(), map_files, and prctl with PR_SET_MM. Adrian
