On Sat, Nov 15, 2014 at 09:37:27AM -0600, Eric W. Biederman wrote: > Josh Triplett <josh@xxxxxxxxxxxxxxxx> writes: > > > Currently, unprivileged processes (without CAP_SETGID) cannot call > > setgroups at all. In particular, processes with a set of supplementary > > groups cannot further drop permissions without obtaining elevated > > permissions first. > > > > Allow unprivileged processes to call setgroups with a subset of their > > current groups; only require CAP_SETGID to add a group the process does > > not currently have. > > A couple of questions. > - Is there precedence in other unix flavors for this? I found a few references to now-nonexistent pages at MIT about a system with this property, but other than that no. I've also found more than a few references to people wanting this functionality. > - What motiviates this change? I have a series of patches planned to add more ways to drop elevated privileges without requiring a transition through root to do so. That would improve the ability for unprivileged users to run programs sandboxed with even *less* privileges. (Among other things, that would also allow programs running with no_new_privs to further *reduce* their privileges, which they can't currently do in this case.) > - Have you looked to see if anything might for bug compatibilty > require applications not to be able to drop supplementary groups? I haven't found any such case; that doesn't mean such a case does not exist. Feedback welcome. The only case I can think of (and I don't know of any examples of such a system): some kind of quota system that limits the members of a group to a certain amount of storage, but places no such limit on non-members. However, the idea of *holding* a credential (a supplementary group ID) giving *less* privileges, and *dropping* a credential giving *more* privileges, would completely invert normal security models. (The sane way to design such a system would be to have a privileged group for "users who can exceed the quota".) If it turns out that a real case exists that people care about, I could easily make this configurable, either at compile time or via a sysctl. - Josh Triplett -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
