Re: [PATCH] gssd: validate cred in gssd_acquire_user_cred

[Simo Sorce <simo@redhat.com>]

On Tue, 2013-10-22 at 16:03 +0000, Weston Andros Adamson wrote:
> On Oct 22, 2013, at 10:41 AM, Simo Sorce <simo@redhat.com> wrote:
> 
> > On Tue, 2013-10-22 at 10:04 -0400, Weston Andros Adamson wrote:
> >> Call gss_inquire_cred after gssd_acquire_krb5_cred check for expired
> >> credentials.
> >> 
> >> This fixes a recent regression (since 302de786930a2c533068f9d8909a817b40f07c32)
> >> that causes the user's ticket cache to grow unbounded with expired service
> >> tickets when the user's credentials expire.
> >> 
> >> To reproduce this issue:
> >> 
> >> - mount kerberos nfs export
> >> - kinit for a short lifetime (ie "kinit -l 1m")
> >> - run a job that opens a file and writes for more than the lifetime
> >> - run klist a few times after expiry and see the list grow, ie:
> >> 
> >> Ticket cache: DIR::/run/user/1749600001/krb5cc/tktYmpGlX
> >> Default principal: dros@APIKIA.FAKE
> >> 
> >> Valid starting       Expires              Service principal
> >> 10/21/2013 15:39:38  10/21/2013 15:40:35  krbtgt/APIKIA.FAKE@APIKIA.FAKE
> >> 10/21/2013 15:39:40  10/21/2013 15:40:35  nfs/zero.apikia.fake@APIKIA.FAKE
> >> 10/21/2013 15:40:35  10/21/2013 15:40:35  nfs/zero.apikia.fake@APIKIA.FAKE
> >> 10/21/2013 15:40:36  10/21/2013 15:40:35  nfs/zero.apikia.fake@APIKIA.FAKE
> >> 10/21/2013 15:40:37  10/21/2013 15:40:35  nfs/zero.apikia.fake@APIKIA.FAKE
> >> 10/21/2013 15:40:37  10/21/2013 15:40:35  nfs/zero.apikia.fake@APIKIA.FAKE
> >> 10/21/2013 15:40:38  10/21/2013 15:40:35  nfs/zero.apikia.fake@APIKIA.FAKE
> >> 10/21/2013 15:40:38  10/21/2013 15:40:35  nfs/zero.apikia.fake@APIKIA.FAKE
> >> 10/21/2013 15:40:39  10/21/2013 15:40:35  nfs/zero.apikia.fake@APIKIA.FAKE
> >> 10/21/2013 15:40:39  10/21/2013 15:40:35  nfs/zero.apikia.fake@APIKIA.FAKE
> >> 10/21/2013 15:40:39  10/21/2013 15:40:35  nfs/zero.apikia.fake@APIKIA.FAKE
> >> 10/21/2013 15:40:39  10/21/2013 15:40:35  nfs/zero.apikia.fake@APIKIA.FAKE
> >> 10/21/2013 15:40:40  10/21/2013 15:40:35  nfs/zero.apikia.fake@APIKIA.FAKE
> >> 10/21/2013 15:40:40  10/21/2013 15:40:35  nfs/zero.apikia.fake@APIKIA.FAKE
> >> 10/21/2013 15:40:41  10/21/2013 15:40:35  nfs/zero.apikia.fake@APIKIA.FAKE
> >> 10/21/2013 15:40:41  10/21/2013 15:40:35  nfs/zero.apikia.fake@APIKIA.FAKE
> >> 10/21/2013 15:40:42  10/21/2013 15:40:35  nfs/zero.apikia.fake@APIKIA.FAKE
> >> 10/21/2013 15:40:42  10/21/2013 15:40:35  nfs/zero.apikia.fake@APIKIA.FAKE
> >> 10/21/2013 15:40:42  10/21/2013 15:40:35  nfs/zero.apikia.fake@APIKIA.FAKE
> >> 
> >> Signed-off-by: Weston Andros Adamson <dros@netapp.com>
> >> ---
> >> utils/gssd/krb5_util.c | 7 +++++++
> >> 1 file changed, 7 insertions(+)
> >> 
> >> diff --git a/utils/gssd/krb5_util.c b/utils/gssd/krb5_util.c
> >> index c6e52fd..ec5db83 100644
> >> --- a/utils/gssd/krb5_util.c
> >> +++ b/utils/gssd/krb5_util.c
> >> @@ -1405,6 +1405,13 @@ gssd_acquire_user_cred(uid_t uid, gss_cred_id_t *gss_cred)
> >> 
> >> 	ret = gssd_acquire_krb5_cred(name, gss_cred);
> >> 
> >> +	/* force validation of cred to check for expiry */
> >> +	if (ret == 0) {
> >> +		if (gss_inquire_cred(min_stat, gss_cred, NULL, NULL,
> >> +				     NULL, NULL) != GSS_S_COMPLETE)
> >> +			ret = -1;
> >> +	}
> >> +
> >> 	maj_stat = gss_release_name(&min_stat, &name);
> >> 	return ret;
> >> }
> > 
> > A good start, but given you are inquiring creds, then I think it would
> > totally make sense to pass in a uint32_t for the 4th argument
> > (lifetime), and check if there is "enough".
> 
> Well, from my perspective gssd already gives enough info for you to know what's going on, i.e.:
> 
> getting credentials for client with uid 1749600001 for server zero.apikia.fake
> CC '/run/user/1749600001/krb5cc' being considered, with preferred realm 'APIKIA.FAKE'
> CC 'DIR:/run/user/1749600001/krb5cc' is expired or corrupt
> WARNING: Failed to create krb5 context for user with uid 1749600001 for server zero.apikia.fake
> doing error downfall
> 
> And it's obvious from the NFS layer as EKEYEXPIRED gets passed through as the error.
> 
> > 
> > For example, if it returns a lifetime of 1 second should we continue ?
> > There is a fat chance that it will fail later on.
> 
> I think how we handle this now (without the regression this fixes) is fine.  I really don't think users/ admins want to enable verbose debugging in gssd to see this - they should be able to tell what happened when the caller gets an expired cred.
> 
> > 
> > I think we should at least log it if the credential we are trying to use
> > turns out to be really close to expiring, no ? It may save some gray
> > hairs to server administrators trying to find out what is going wrong
> > (like it happened to you :)
> 
> Well, it was obvious to me what was happening when the keys expired - what was not obvious was why the tkt cache was growing unbounded with service tickets that were *never* valid (the regression this patch fixes).
> 
> I suppose we could do something more, but I don't really see a reason to.


you are probably right,

Reviewed-by: Simo Sorce <simo@redhat.com>

Simo.

-- 
Simo Sorce * Red Hat, Inc * New York