[PATCH BUG 13478] krb5_wrap: fix keep_old_entries logic for older kerberos libraries

[Alexander Bokovoy]

On ti, 19 kesä 2018, Christof Schmitt via samba-technical wrote:
> From 0814f429c311b315362d27fd884d3ea58f484210 Mon Sep 17 00:00:00 2001
> From: Christof Schmitt <cs at samba.org>
> Date: Tue, 19 Jun 2018 15:09:41 -0700
> Subject: [PATCH] krb5_wrap: fix keep_old_entries logic for older kerberos
>  libraries
> 
> MIT kerberos 1.13 and older only stores the 8 bits of the KVNO. The
> change from commit 35b2fb4ff32 resulted in breakage for these kerberos
> versions: 'net ads keytab create' reads a large KVNO from AD, and only
> the lower 8 bits are stored. The next check then removed the entry again
> as the 8bit value did not match the currently valid KVNO.
> 
> Fix this by limiting the check to only 8 bits.
> 
> BUG: https://bugzilla.samba.org/show_bug.cgi?id=13478
> 
> Signed-off-by: Christof Schmitt <cs at samba.org>
> ---
>  lib/krb5_wrap/krb5_samba.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/lib/krb5_wrap/krb5_samba.c b/lib/krb5_wrap/krb5_samba.c
> index f49838c..7e90913 100644
> --- a/lib/krb5_wrap/krb5_samba.c
> +++ b/lib/krb5_wrap/krb5_samba.c
> @@ -1549,7 +1549,7 @@ krb5_error_code smb_krb5_kt_seek_and_delete_old_entries(krb5_context context,
>  		}
>  
>  		if (!flush &&
> -		    (kt_entry.vno == kvno) &&
> +		    ((kt_entry.vno & 0xff) == (kvno & 0xff)) &&
>  		    (kt_entry_enctype != enctype))
>  		{
>  			DEBUG(5, (__location__ ": Saving entry with kvno [%d] "
> -- 
> 1.8.3.1

A few lines above in the same function we already cut off to 8-bit since
2015.

RB+. Please push.

We need eventually to extend the code to handle 32-bit versions but this
comment from 'more_recent()' helper in MIT krb5 does not make it optimistic:

    /*
     * If a small kvno was written at the same time or later than a large kvno,
     * the kvno probably wrapped at some boundary, so consider the small kvno
     * more recent.  Wraparound can happen due to pre-1.14 keytab file format
     * limitations (8-bit kvno storage), pre-1.14 kadmin protocol limitations
     * (8-bit kvno marshalling), or KDB limitations (16-bit kvno storage).
     */


-- 
/ Alexander Bokovoy