On Tue, Sep 29, 2015 at 4:54 PM, Andreas Grünbacher <andreas.gruenbacher@xxxxxxxxx> wrote: > 2015-09-28 19:46 GMT+02:00 J. Bruce Fields <bfields@xxxxxxxxxxxx>: >> On Mon, Sep 28, 2015 at 07:10:06PM +0200, Andreas Grünbacher wrote: >>> 2015-09-28 18:35 GMT+02:00 J. Bruce Fields <bfields@xxxxxxxxxxxx>: >>> > On Mon, Sep 28, 2015 at 12:08:51AM +0200, Andreas Gruenbacher wrote: >>> >> Open issues in nfs: >>> >> >>> >> * When a user or group name cannot be mapped, nfs's idmapper always maps it >>> >> to nobody. That's good enough for mapping the file owner and owning >>> >> group, but not for identifiers in acls. For now, to get the nfs richacl >>> >> support somewhat working, I'm explicitly checking if mapping has resulted >>> >> in uid/gid 99 in the kernel. >>> >> >>> >> * When the nfs server replies with NFS4ERR_BADNAME for any user or group >>> >> name lookup, the client will stop sending numeric uids and gids to the >>> >> server even when the lookup wasn't numeric. From then on, the client >>> >> will translate uids and gids that have no mapping to the string "nobody", >>> >> and the server will reject them. This problem is not specific to acls. >>> > >>> > Do you have fixes in mind for these two issues? >>> >>> I'm not sure how to best fix the idmapper problem, with backwards >>> compatibility and all. >> >> I haven't looked at the current nfsidmap interface.... So it's >> completely lacking any way to communicate failure? > > Yes, when a user doesn't exist, idmapper maps that to the nobody > uid/gid. That's the failure mode of stat. In the acl case, we do want > to map user and group names to their respective ids where possible (so > that the acl makes sense in the local system context), but we do want > to preserve the original user and group names when there is no such > mapping instead of mapping to the nobody uid/gid. So that's fixed now in nfs-utils and the latest richacl snapshot. >>> The second problem shouldn't be too hard to fix. >> >> Is it enough to turn off the failover in the case there's no possibility >> it could have been caused by a numeric id? > > Yes, I believe that would be enough. > >> If any user can set ACLs with arbitrary strings as names, then we'd be >> giving any user unprivileged user the ability to turn off numeric >> idmapping, so I think we need to fix that. > > The bug can be triggered by unprivileged users with nfs4_setfacl. It turns out that when setting an ACL, the ACL can contain UID/GID numbers as well as user@domain strings which the server cannot map. The status code is NFS4ERR_BADNAME both when the server doesn't support UID/GID numbers and when it cannot map a name, so in that case, we cannot tell the difference. Luckily, when a UID/GID cannot be mapped to a name, nfs falls back to sending the server a UID/GID number instead even when NFS_CAP_UIDGID_NOMAP has been cleared. So unprivileged users can turn on the idmapper, but at least that doesn't break unmapped UIDs/GIDs. (I got that wrong in my initial analysis.) Thanks, Andreas -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
