bug with SGN_ALG_MD2_5 case handling in kg_unseal_v1()?

[Will Fiveash]

On Fri, Apr 14, 2017 at 02:12:47AM -0400, Greg Hudson wrote:
> On 04/13/2017 03:55 PM, Will Fiveash wrote:
> > In src/lib/gssapi/krb5/k5unseal.c:kg_unseal_v1() at line 381 which is
> > part of the case SGN_ALG_MD2_5 block I see:
> > 
> >         code = k5_bcmp(md5cksum.contents, ptr + 14, 8);
> >         /* Falls through to defective-token??  */
> > 
> >     default:
> >         *minor_status = 0;
> >         return(GSS_S_DEFECTIVE_TOKEN);
> > 
> > This seems like a bug given the processing that precedes this, thoughts?
> 
> It does look like a bug.  The code's been like that since 1.0; the
> comment was added in 1.2.  It would seem that unwrapping tokens using
> SGN_ALG_MD2_5 never worked, and we could probably get rid of the code.
> Neither our code nor Heimdal's appears to choose SGN_ALG_MD2_5 when
> creating tokens, by my reading.
> 
> (According to RFC 1964, "MD2.5" refers to using half of the 128-bit MD5
> checksum; it doesn't actually reference the MD2 hash algorithm.)

It would be good to delete that code as it was flagged during recent
code checking for improper case fall-throughs.

-- 
Will Fiveash
Oracle Solaris Software Engineer