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.
