krb5 commit: Fix SPNEGO fallback context handling

https://github.com/krb5/krb5/commit/40ecfad10dd36700028ff0f3d0d79ce7925fe545
commit 40ecfad10dd36700028ff0f3d0d79ce7925fe545
Author: Greg Hudson <[email protected]>
Date:   Mon Nov 11 12:25:41 2019 -0500

    Fix SPNEGO fallback context handling
    
    In init_ctx_call_init(), if gss_init_sec_context() fails while
    producing the first SPNEGO initiator token, we remove the first
    candidate mechanism from sc->mech_set and try again.  If
    sc->ctx_handle is present after the error (more likely after commit
    56f7b1bc95a2a3eeb420e069e7655fb181ade5cf), we must clear it before
    falling back or it will cause subsequent attempts to fail.
    
    ticket: 8846 (new)
    tags: pullup
    target_version: 1.17-next
    target_version: 1.16-next

 src/lib/gssapi/spnego/spnego_mech.c |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)

diff --git a/src/lib/gssapi/spnego/spnego_mech.c b/src/lib/gssapi/spnego/spnego_mech.c
index 5f92cb6..9123d9c 100644
--- a/src/lib/gssapi/spnego/spnego_mech.c
+++ b/src/lib/gssapi/spnego/spnego_mech.c
@@ -972,6 +972,7 @@ init_ctx_call_init(OM_uint32 *minor_status,
 	gss_release_buffer(&tmpmin, &sc->DER_mechTypes);
 	if (put_mech_set(sc->mech_set, &sc->DER_mechTypes) < 0)
 		goto fail;
+	gss_delete_sec_context(&tmpmin, &sc->ctx_handle, GSS_C_NO_BUFFER);
 	tmpret = init_ctx_call_init(&tmpmin, sc, spcred, acc_negState,
 				    target_name, req_flags, time_req,
 				    mechtok_in, mechtok_out, time_rec,