On Fri, 2017-02-10 at 14:29 -0500, Jeff Layton wrote: > On Fri, 2017-02-10 at 14:14 -0500, Simo Sorce wrote: > > On Fri, 2017-02-10 at 13:30 -0500, Jeff Layton wrote: > > > On Fri, 2017-02-10 at 12:39 -0500, Jeff Layton wrote: > > > > On Fri, 2017-02-10 at 11:15 -0600, Chad William Seys wrote: > > > > > Hi Jeff, > > > > > > > > > > > So we have a default credcache for the user for whom we are > > > > > > operating > > > > > > as, but we can't get the default principal name from it. My > > > > > > guess is > > > > > > that it's not finding the > > > > > > > > > > This mount is run by root UID=0 and seems to be find that > > > > > credential > > > > > cache without problem (earlier in the logs). The problem > > > > > seems > > > > > to come > > > > > in when it tries to find the cache for user with UID=1494 . > > > > > > > > > > I'm wondering if the scan of /tmp was helpful for finding > > > > > caches > > > > > of > > > > > non-same users. > > > > > > > > > > (I'm a little surprised that there is any attempt to find > > > > > credentials of > > > > > the non-root user at mount time - what happens if the non- > > > > > root > > > > > user > > > > > hasn't kinit-ed yet? And yet that case worked in the > > > > > past...) > > > > > > > > > > > > > I'm more interested in what the trailing info in your credcache > > > > name is. > > > > In your log output for the working case, there are: > > > > > > > > /tmp/krb5cc_0 > > > > /tmp/krb5cc_1494_sM11PG > > > > > > > > So first one doesn't have that _XXXXXX trailing bit. Maybe > > > > cifs.upcall > > > > is not guessing that piece of the filename correctly? > > > > > > > > > > (cc'ing Nalin, Simo and the linux-cifs ml) > > > > > > Yeah, it seems pretty likely that that is the problem. My guess > > > is > > > that > > > the extra stuff on the ccname is coming from pam_krb5, which > > > seems to > > > want to create a credcache that is session-specific. > > > > > > You could play with setting a different ccname_template for > > > pam_krb5 > > > that doesn't have the trailing stuff at the end, but it looks > > > like it > > > won't clean them up on logout if you do that. Caveat emptor. > > > > > > I'm not sure what the right solution is there. For Simo and > > > Nalin: > > > > > > The upshot here is that we did a big clean up of the cifs-utils > > > code > > > recently, to get it out of the business of scanning /tmp for > > > credcaches. > > > That allows us to have better compatibility with other credcache > > > types > > > (keyring or whatever), and it was always rather nasty anyway. > > > > > > pam_krb5 wants to make session-specific credcaches however, and > > > cifs.upcall can't easily guess them. cifs.upcall is called from > > > the > > > kernel, so it can't look in the environment or anything to find > > > the > > > credcache. > > > > > > What's the right approach to fix this? Are we stuck with scanning > > > /tmp > > > forever? > > > > I think the right approach in the long run will be the KCM we are > > building in SSSD and planning to make the default cache type for > > F26. > > > > For file ccaches you are out of luck, even scanning /tmp can fail > > as > > users can decide to put them elsewhere. > > > > If a scan need to be made I would rather stat the files and look > > which > > one belong to the user that start with "/tmp/krb" rather than > > trying to > > guess the file name. Keep in mind predictable file names in /tmp > > are > > really not an option so pam_krb5 is doing the right thing in using > > a > > randomized file name given it runs as root. > > > > Well, that's what we used to do -- do a readdir in /tmp, start > looking for files that might be credcaches. Of course that meant we > have to carry around a bunch of cruft for handling FILE: credcaches > that doesn't really adapt well to DIR: or KEYRING: ones. > > I guess I have a philosophical question: how is an application (like > cifs.upcall), which is not descended from the user's session expected > to find a user's credcache? Is that use-case just not really > accounted for buy the krb5 libs? Yeah it is not accounted for, it is assumed that applications are given a ccache name by the caller or in KRB5CCNAME. The fact the kernel operates this way was not on the radar in the intial design. > One thing we could do (though I really don't like it), is to take the > pid value passed in the upcall and scrape that task's > /proc/<pid>/environ file for KRB5CCNAME=. That really is pretty nasty > though. Yeah it is, and it is probably also not fully reliable, but it may be the best way to go in the short term. I think the only way will be the KCM, although it would be really nice if the KCM could be given a session id of some kind, because it would be nice to be able to have different ccaches in different sessions. However for the general case and NFS/CIFS in particular I think KCM will be the right way to go and will be sufficient to just talk to it "as the user" (ie with a setuid like nfs utils does). Simo. -- To unsubscribe from this list: send the line "unsubscribe linux-cifs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
