On Wed, Nov 13, 2013 at 11:23:46AM +1100, NeilBrown wrote: > On Tue, 12 Nov 2013 11:16:34 -0500 "J. Bruce Fields" <bfields@xxxxxxxxxxxx> > wrote: > > > On Tue, Nov 12, 2013 at 05:29:46AM +0000, Myklebust, Trond wrote: > > > > > > On Nov 12, 2013, at 0:11, NeilBrown <neilb@xxxxxxx> wrote: > > > > > > > On Mon, 11 Nov 2013 15:33:14 -0500 Chuck Lever <chuck.lever@xxxxxxxxxx> wrote: > > > > > > > >> > > > >> On Nov 11, 2013, at 1:59 PM, Steve Dickson <SteveD@xxxxxxxxxx> wrote: > > > >> > > > >>> On 11/11/13 13:30, Chuck Lever wrote: > > > >>>> > > > >>>> On Nov 11, 2013, at 1:06 PM, Steve Dickson <SteveD@xxxxxxxxxx> wrote: > > > >>>> > > > >>>>> > > > >>>>> > > > >>>>> On 09/11/13 18:12, Myklebust, Trond wrote: > > > >>>>>> One alternative to the above scheme, which I believe that I’ve > > > >>>>>> suggested before, is to have a permanent entry in rpc_pipefs > > > >>>>>> that rpc.gssd can open and that the kernel can use to detect > > > >>>>>> that it is running. If we make it /var/lib/nfs/rpc_pipefs/gssd/clnt00/gssd, > > > >>>>>> then AFAICS we don’t need to change nfs-utils at all, since all newer > > > >>>>>> versions of rpc.gssd will try to open for read anything of the form > > > >>>>>> /var/lib/nfs/rpc_pipefs/*/clntXX/gssd... > > > >>>>> > > > >>>>> After further review I am going going have to disagree with you on this. > > > >>>>> Since all the context is cached on the initial mount the kernel > > > >>>>> should be using the call_usermodehelper() to call up to rpc.gssd > > > >>>>> to get the context, which means we could put this upcall noise > > > >>>>> to bed... forever! :-) > > > >>>> > > > >>>> Ask Al Viro for his comments on whether the kernel should start > > > >>>> gssd (either a daemon or a script). Hint: wear your kevlar underpants. > > > >>> I was thinking gssd would become a the gssd-cmd command... Al does not > > > >>> like the call_usermodehelper() interface? > > > >> > > > >> He doesn't have a problem with call_usermodehelper() in general. However, the kernel cannot guarantee security if it has to run a fixed command line. Go ask him to explain. > > > >> > > > >> > > > >>> > > > >>>> > > > >>>> Have you tried Trond's approach yet? > > > >>> Looking into it... But nothing is trivial in that code... > > > >>> > > > >>>> > > > >>>>> I realize this is not going happen overnight, so I would still > > > >>>>> like to propose my nfs4_secure_mounts bool patch as bridge > > > >>>>> to the new call_usermodehelper() since its the cleanest > > > >>>>> solution so far... > > > >>>>> > > > >>>>> Thoughts? > > > >>>> > > > >>>> We have workarounds already that work on every kernel since 3.8. > > > >>>> > > > >>> The one that logs 5 to 20 lines (depending on thins are setup or not) > > > >>> per mount? That does work in some environments but no all. ;-) > > > >> > > > >> When does running rpc.gssd not work? > > > > > > > > Oohh ooh.. Pick me. Pick me!! I can answer that one. > > > > > > > > Running rpc.gssd does not work if you are mounting a filesystem using the IP > > > > address of the server and that IP address doesn't have a matching hostname > > > > anywhere that can be found: > > > > > > > > In a newly creating minimal kvm install without rpc.gssd running, > > > > mount 10.0.2.2:/home /mnt > > > > > > > > sleeps for 15 seconds then succeeds. > > > > If I start rpc.gssd, then the same command takes forever. > > > > > > > > strace of rpc.gssd shows that it complains about not being able to resolve > > > > the host name and "ERROR: failed to read service info". Then it keeps the > > > > pipes open but never sends any message on them, so the kernel just keeps on > > > > waiting. > > > > > > > > If I change "fail_keep_client" to "fail_destroy_client", then it closes the > > > > pipe and we get the 15 second timeout back. > > > > If I change NI_NAMEREQD to 0, then the mount completes instantly. (of course > > > > that make serious compromise security so it was just for testing). > > > > (Adding an entry to /etc/hosts also gives instant success). > > > > > > > > I'm hoping that someone who understands this code will suggest something > > > > clever so I don't have to dig through all of it ;-) > > > > > > rpc.gssd is supposed to do a downcall with a zero-length window and an error message in any situation where it cannot establish a GSS context. Normally, I’d expect an EACCES for the above scenario. > > > > > > IOW: that’s a blatant rpc.gssd bug. One that will also affect you when you're doing NFSv3 and add ‘sec=krb5’ to the mount options. > > > > Also why is gssd trying to do a DNS lookup in this case? This sounds > > similar to what f9f5450f8f94 "Avoid DNS reverse resolution for server > > names (take 3)" was trying to fix? > > It is quite possible that I misunderstand something. But this is my > understanding. > > 1/ "mount" allows you to use either an IP address or a host name to mount a > filesystem. > 2/ gss requires a hostname to identify the server and find it's key (IP not > sufficient). > 3/ If you use a host name to mount a filesystem, then that exact same host > name should be used by gssd to identify the server and its key. > The above mentioned patch was trying to enforce this. The idea was to > collect the name given to the 'mount', see if it looked like an IP address > or a Server name. If the later, just use it. If the former, do a reverse > lookup because an IP address is no use by itself for gss. > Previously it would always do a reverse DNS lookup from the IP address > that was determined from the server-name-or-IP-address. > Unfortunately this patch was broken - got the test backwards. > A follow-up patch fixed the test: c93e8d8eeafec3e32 > > 4/ So the above patch was not intended to address the case of mount-by-IP > address at all - and this is the case that is causing me problems. OK, but it still seems dumb to even attempt the reverse lookup: the lookup probably isn't secure, and the mount commandline should have a name that we can match to a krb5 principal without needing any other lookups. So I'd think reasonable behavior in this case would be to just try the IP address on the chance there's actually an nfs/x.y.z.w@REALM principal. (Or just fail outright if kerberos doesn't allow principals that look like that.) --b. -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
