Serge Hallyn <serge.hallyn@xxxxxxxxxxxxx> writes: > Quoting Eric W. Biederman (ebiederm@xxxxxxxxxxxx): >> Serge Hallyn <serge.hallyn@xxxxxxxxxxxxx> writes: >> >> > Quoting Eric W. Biederman (ebiederm@xxxxxxxxxxxx): >> >> From: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx> >> >> >> >> To keep things sane in the context of file descriptor passing derive the >> >> user namespace that uids are mapped into from the opener of the file >> >> instead of from current. >> >> >> >> When writing to the maps file the lower user namespace must always >> >> be the parent user namespace, or setting the mapping simply does >> >> not make sense. Enforce that the opener of the file was in >> >> the parent user namespace or the user namespace whose mapping >> >> is being set. >> > >> > Is there a reasonable use case for writing from the ns whose mapping >> > is being set? Are you expecting cases where the child opens the file >> > and passes it back to the parent to set the mappings? >> >> Passing the open mappings file no. Although by using seq_user_ns I do >> make certain the semantics are correct if the file descriptor is passed, >> but I did that on general principles. >> >> I expect a process in the user namespace to be able to meaningfully set >> the mapping to some the current uid and the current gid. > > Sorry, I think a word is missing there. To be precise (bc I haven't > thought about this much before as it's not my target goal :) you're > saying if I'm uid 1000 gid 1000, I can create a new user namespace > and, from inside that new userns (where I'm first uid/gid -1) I can > map any uid+gid in the container to 1000 in the parent ns? Or is there > something more? Only that for now. I had once imagined magic would happen in the background to verify the parent. > It still seems to me no less flexible to require being in the parent > ns, so > >> >> + if ((seq_ns != ns) && (seq_ns != ns->parent)) >> >> + return -EPERM; > > would become > >> >> + if (seq_ns != ns->parent) >> >> + return -EPERM; > In practice when playing around it is the difference between. unshare -U /bin/bash echo 0 1000 1 > /proc/self/uid_map And the need to pre-plan something. You can set the uid_map from the parent in a shell script but it is a real pain. So for just messing around allowing seq_ns == ns is a real advantage. > I also wonder if -EINVAL would be a more appropriate choice here. > We're trying to keep things sane, rather than saying "not allowed" > for its own sake. A different error code might be better. Eric -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
