> 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?
