"Serge E. Hallyn" <serge@xxxxxxxxxx> writes: > On Mon, Oct 12, 2020 at 07:05:10PM +0200, Giuseppe Scrivano wrote: >> Josh Triplett <josh@xxxxxxxxxxxxxxxx> writes: >> >> > On Fri, Oct 09, 2020 at 11:26:06PM -0500, Serge E. Hallyn wrote: >> >> > 3. Find a way to allow setgroups() in a user namespace while keeping >> >> > in mind the case of groups used for negative access control. >> >> > This was suggested by Josh Triplett and Geoffrey Thomas. Their idea was to >> >> > investigate adding a prctl() to allow setgroups() to be called in a user >> >> > namespace at the cost of restricting paths to the most restrictive >> >> > permission. So if something is 0707 it needs to be treated as if it's 0000 >> >> > even though the caller is not in its owning group which is used for negative >> >> > access control (how these new semantics will interact with ACLs will also >> >> > need to be looked into). >> >> >> >> I should probably think this through more, but for this problem, would it >> >> not suffice to add a new prevgroups grouplist to the struct cred, maybe >> >> struct group_info *locked_groups, and every time an unprivileged task creates >> >> a new user namespace, add all its current groups to this list? >> > >> > So, effectively, you would be allowed to drop permissions, but >> > locked_groups would still be checked for restrictions? >> > >> > That seems like it'd introduce a new level of complexity (a new facet of >> > permission) to manage. Not opposed, but it does seem more complex than >> > just opting out of using groups for negative permissions. >> >> I have played with something similar in the past. At that time I've >> discussed it only privately with Eric and we agreed it wasn't worth the >> extra complexity: >> >> https://github.com/giuseppe/linux/commit/7e0701b389c497472d11fab8570c153a414050af > > Hi, you linked the setgroups patch, but do you also have a link to the > attempt which you deemed was not worth it? it was just part of a private discussion; but was 4 years ago so we can probably revisit and accept the additional complexity since setgroups() is still an issue with user namespaces. >> instead of a prctl, I've added a new mode to /proc/PID/setgroups that >> allows setgroups in a userns locking the current gids. >> >> What do you think about using /proc/PID/setgroups instead of a new >> prctl()? > > It's better than not having it, but two concerns - > > 1. some userspace, especially testsuites, could become confused by the fact > that they can't drop groups no matter how hard they try, since these will all > still show up as regular groups. I forgot to send a link to a second patch :-) that completes the feature: https://github.com/giuseppe/linux/commit/1c5fe726346b216293a527719e64f34e6297f0c2 When the new mode is used, the gids that are not known in the userns do not show up in userspace. > 2. whereas in my lockgroups proposal, lock_groups would only be taken into account > for permission denial, this proposal would count for permission grants too. This > means that if I have a group which is permitted to read /foo/topsecret, and I > start a program in a new user namespace expecting it to drop that permission, > I can't have that, right? The new program, will always have that permission? right. The new mode I was working on cannot be used to drop granted permissions. Giuseppe _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/containers
