On Mon, 17 Nov 2025, Tyler W. Ross wrote: > Weird behavior I just discovered: > > Explicitly setting allowed-enctypes in the gssd section of /etc/nfs.conf > to exclude aes256-cts-hmac-sha1-96 makes both SHA2 ciphers work as > expected (assuming each is allowed). > > If allowed-enctypes is unset (letting gssd interrogate the kernel for > supported enctypes) or includes aes256-cts-hmac-sha1-96, then the XDR > overflow occurs. > > Non-working configurations (first is the commented-out default in nfs.conf): > allowed-enctypes=aes256-cts-hmac-sha384-192,aes128-cts-hmac-sha256-128,camellia256-cts-cmac,camellia128-cts-cmac,aes256-cts-hmac-sha1-96,aes128-cts-hmac-sha1-96 > allowed-enctypes=aes256-cts-hmac-sha384-192,aes256-cts-hmac-sha1-96 > allowed-enctypes=aes128-cts-hmac-sha256-128,aes256-cts-hmac-sha1-96 > allowed-enctypes=aes256-cts-hmac-sha384-192,aes128-cts-hmac-sha256-128,aes256-cts-hmac-sha1-96 > > Working configurations (first is default sans aes256-cts-hmac-sha1-96): > allowed-enctypes=aes256-cts-hmac-sha384-192,aes128-cts-hmac-sha256-128,camellia256-cts-cmac,camellia128-cts-cmac,aes128-cts-hmac-sha1-96 > allowed-enctypes=aes256-cts-hmac-sha384-192,aes128-cts-hmac-sha256-128 > allowed-enctypes=aes256-cts-hmac-sha384-192,aes128-cts-hmac-sha1-96 > allowed-enctypes=aes128-cts-hmac-sha256-128,aes128-cts-hmac-sha1-96 >
That doesn't really make sense. You should only need to use the allowed-enctypes setting if you're talking to an NFS server that doesn't have support for the new encryption types. It basically works like the "permitted_enctypes" option in krb5.conf, except it only affects NFS rather than affecting your krb5 configuration as a whole. Can you go back and re-do the tracepoint capture, except this time umount your NFS filessytems before starting the capture (i.e. perform the mount command while trace-cmd is running). I'm curious what values the rpcgss_update_slack tracepoint shows. > > Is this gssd mishandling some setup/initialization? > Or is there a miscalculation happening somewhere further up? > > > TWR >
