XPost: linux.debian.bugs.dist, linux.kernel   
   From: smayhew@redhat.com   
      
   On Tue, 18 Nov 2025, Tyler W. Ross wrote:   
      
   > On 11/17/25 3:54 PM, Scott Mayhew wrote:   
   > > FWIW I have both Debian Trixie and Sid/Forky VMs, and krb5{,i,p} is   
   > > working across the board for me.  Normally I just use a plain MIT KDC,   
   > > so I tried IPA and that works fine too.   
   >    
   > Did you confirm the enctype used?   
      
   Yes.  This is how I was testing:   
      
   root@forky:~# uname -r   
   6.17.7+deb14+1-amd64   
   root@forky:~# systemctl restart rpc-gssd   
   root@forky:~# klist -ce /tmp/krb5ccmachine_SMAYHEW.TEST   
   klist: No credentials cache found (filename: /tmp/krb5ccmachine_SMAYHEW.TEST)   
   root@forky:~# for serv in forky trixie rawhide rhel10 rhel9; do for flav in   
   krb5 krb5i krb5p; do mount -o v4.2,sec=$flav $serv.smayhew.test:/export   
   /mnt/t; ls -lR /mnt/t >/dev/null; umount /mnt/t; done; done   
   root@forky:~# klist -ce /tmp/krb5ccmachine_SMAYHEW.TEST   
   Ticket cache: FILE:/tmp/krb5ccmachine_SMAYHEW.TEST   
   Default principal: nfs/forky.smayhew.test@SMAYHEW.TEST   
      
   Valid starting     Expires            Service principal   
   11/14/25 14:53:03  11/15/25 14:53:03  krbtgt/SMAYHEW.TEST@SMAYHEW.TEST   
           Etype (skey, tkt): aes256-cts-hmac-sha384-192, aes256-ct   
   -hmac-sha384-192   
   11/14/25 14:53:03  11/15/25 14:53:03  nfs/forky.smayhew.test@SMAYHEW.TEST   
           Etype (skey, tkt): aes256-cts-hmac-sha384-192, aes256-ct   
   -hmac-sha384-192   
   11/14/25 14:53:03  11/15/25 14:53:03  nfs/trixie.smayhew.test@SMAYHEW.TEST   
           Etype (skey, tkt): aes256-cts-hmac-sha384-192, aes256-ct   
   -hmac-sha384-192   
   11/14/25 14:53:03  11/15/25 14:53:03  nfs/rawhide.smayhew.test@SMAYHEW.TEST   
           Etype (skey, tkt): aes256-cts-hmac-sha384-192, aes256-ct   
   -hmac-sha384-192   
   11/14/25 14:53:04  11/15/25 14:53:03  nfs/rhel10.smayhew.test@SMAYHEW.TEST   
           Etype (skey, tkt): aes256-cts-hmac-sha384-192, aes256-ct   
   -hmac-sha384-192   
   11/14/25 14:53:05  11/15/25 14:53:03  nfs/rhel9.smayhew.test@SMAYHEW.TEST   
           Etype (skey, tkt): aes256-cts-hmac-sha384-192, aes256-ct   
   -hmac-sha384-192   
      
   >    
   > My repro steps, from initial mounted state:   
   > kinit   
   > kvno -e aes256-cts-hmac-sha384-192    
   > ls /mnt/example   
   >    
   > On my Debian Sid VM, if I do kinit and then immediately ls, the issue    
   > does not occur. klist shows the acquired service ticket has an   
   > aes256-cts-hmac-sha1-96 session key.   
      
   Oh!  I see the problem.  If the automatically acquired service ticket   
   for a normal user is using aes256-cts-hmac-sha1-96, then I'm assuming   
   the machine credential is also using aes256-cts-hmac-sha1-96.   
   Run 'klist -ce /tmp/krb5ccmachine_IPA.TWRLAB.NET' to check.  You can't   
   use 'kvno -e' to choose a different encryption type.  Why are you doing   
   that?  Is it because you want to use the stronger encryption types?  In   
   that case, the proper way to do this would be to manually add this line   
   to the "[libdefaults]" stanza of your /etc/krb5.conf:   
      
     permitted_enctypes = aes256-cts-hmac-sha384-192 aes128-cts-hmac-sha256-128   
   aes256-cts-hmac-sha1-96 aes128-cts-hmac-sha1-96   
      
   and get rid of allowed-enctypes settings that you may have added to   
   /etc/nfs.conf.  Then unmount, run 'systemctl restart rpc-gssd', remount,   
   etc. and your system should be using aes256-cts-hmac-sha384-192 by default.   
      
   RHEL/CentOS/Fedora all ship a package called "crypto-policies" that   
   include system-wide configurations for various crypto packages.  For   
   kerberos, it drops a config snippet in /etc/krb5.conf.d similar to what   
   I have above.  AFAICT Suse has this package too, but it appears Debian   
   does not.   
      
   Without the permitted_enctypes setting, the kerberos library will fall   
   back to the default settings, which according to krb5.conf(5)    
      
   ---8<---   
          permitted_enctypes   
                 Identifies the encryption types that servers will permit for   
   ses‐   
                 sion keys and for ticket and authenticator encryption, ordered by   
                 preference from highest to lowest.   Starting  in  release  1.18,   
                 this  tag also acts as the default value for default_tgs_enctypes   
                 and default_tkt_enctypes.  The default  value  for  this  tag  is   
                 aes256-cts-hmac-sha1-96                   aes128-cts-hmac-sha1-96   
                 aes256-cts-hmac-sha384-192             aes128-cts-hmac-sha256-128   
                 des3-cbc-sha1    arcfour-hmac-md5   camellia256-cts-cmac     
   camel‐   
                 lia128-cts-cmac.   
   ---8<---   
      
   If I remove that line from my krb5.conf and use 'kvno -e' like your   
   test, then I can reproduce the behavior you're seeing:   
      
   root@forky:~# systemctl restart rpc-gssd   
   root@forky:~# mount -o v4.2,sec=krb5 trixie.smayhew.test:/export /mnt/t   
      
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