Code: spnego_gss_init_sec_context(
			OM_uint32 *minor_status,
			gss_cred_id_t claimant_cred_handle,
			gss_ctx_id_t *context_handle,
			gss_name_t target_name,
			gss_OID mech_type,
			OM_uint32 req_flags,
			OM_uint32 time_req,
			gss_channel_bindings_t input_chan_bindings,
			gss_buffer_t input_token,
			gss_OID *actual_mech,
			gss_buffer_t output_token,
			OM_uint32 *ret_flags,
			OM_uint32 *time_rec)
{
	send_token_flag send_token = NO_TOKEN_SEND;
	OM_uint32 tmpmin, ret, negState;
	gss_buffer_t mechtok_in, mechListMIC_in, mechListMIC_out;
	gss_buffer_desc mechtok_out = GSS_C_EMPTY_BUFFER;
	spnego_gss_cred_id_t spcred = NULL;
	spnego_gss_ctx_id_t spnego_ctx = NULL;

	dsyslog("Entering init_sec_context\n");

	mechtok_in = mechListMIC_out = mechListMIC_in = GSS_C_NO_BUFFER;
	negState = REJECT;

	/*
	 * This function works in three steps:
	 *
	 *   1. Perform mechanism negotiation.
	 *   2. Invoke the negotiated or optimistic mech's gss_init_sec_context
	 *      function and examine the results.
	 *   3. Process or generate MICs if necessary.
	 *
	 * The three steps share responsibility for determining when the
	 * exchange is complete.  If the selected mech completed in a previous
	 * call and no MIC exchange is expected, then step 1 will decide.  If
	 * the selected mech completes in this call and no MIC exchange is
	 * expected, then step 2 will decide.  If a MIC exchange is expected,
	 * then step 3 will decide.  If an error occurs in any step, the
	 * exchange will be aborted, possibly with an error token.
	 *
	 * negState determines the state of the negotiation, and is
	 * communicated to the acceptor if a continuing token is sent.
	 * send_token is used to indicate what type of token, if any, should be
	 * generated.
	 */

	/* Validate arguments. */
	if (minor_status != NULL)
		*minor_status = 0;
	if (output_token != GSS_C_NO_BUFFER) {
		output_token->length = 0;
		output_token->value = NULL;
	}
	if (minor_status == NULL ||
	    output_token == GSS_C_NO_BUFFER ||
	    context_handle == NULL)
		return GSS_S_CALL_INACCESSIBLE_WRITE;

	if (actual_mech != NULL)
		*actual_mech = GSS_C_NO_OID;

	/* Step 1: perform mechanism negotiation. */
	spcred = (spnego_gss_cred_id_t)claimant_cred_handle;
	if (*context_handle == GSS_C_NO_CONTEXT) {
		ret = init_ctx_new(minor_status, spcred,
				   context_handle, &send_token);
		if (ret != GSS_S_CONTINUE_NEEDED) {
			goto cleanup;
		}
	} else {
		ret = init_ctx_cont(minor_status, context_handle,
				    input_token, &mechtok_in,
				    &mechListMIC_in, &negState, &send_token);
		if (HARD_ERROR(ret)) {
			goto cleanup;
		}
	}

	/* Step 2: invoke the selected or optimistic mechanism's
	 * gss_init_sec_context function, if it didn't complete previously. */
	spnego_ctx = (spnego_gss_ctx_id_t)*context_handle;
	if (!spnego_ctx->mech_complete) {
		ret = init_ctx_call_init(
			minor_status, spnego_ctx, spcred,
			target_name, req_flags,
			time_req, mechtok_in,
			actual_mech, &mechtok_out,
			ret_flags, time_rec,
			&negState, &send_token);

		/* Give the mechanism a chance to force a mechlistMIC. */
		if (!HARD_ERROR(ret) && mech_requires_mechlistMIC(spnego_ctx))
			spnego_ctx->mic_reqd = 1;
	}

	/* Step 3: process or generate the MIC, if the negotiated mech is
	 * complete and supports MICs. */
	if (!HARD_ERROR(ret) && spnego_ctx->mech_complete &&
	    (spnego_ctx->ctx_flags & GSS_C_INTEG_FLAG)) {

		ret = handle_mic(minor_status,
				 mechListMIC_in,
				 (mechtok_out.length != 0),
				 spnego_ctx, &mechListMIC_out,
				 &negState, &send_token);
	}
cleanup:
	if (send_token == INIT_TOKEN_SEND) {
		if (make_spnego_tokenInit_msg(spnego_ctx,
					      0,
					      mechListMIC_out,
					      req_flags,
					      &mechtok_out, send_token,
					      output_token) < 0) {
			ret = GSS_S_FAILURE;
		}
	} else if (send_token != NO_TOKEN_SEND) {
		if (make_spnego_tokenTarg_msg(negState, GSS_C_NO_OID,
					      &mechtok_out, mechListMIC_out,
					      send_token,
					      output_token) < 0) {
			ret = GSS_S_FAILURE;
		}
 	}
 	gss_release_buffer(&tmpmin, &mechtok_out);
 	if (ret == GSS_S_COMPLETE) {
		/*
		 * Now, switch the output context to refer to the
		 * negotiated mechanism's context.
		 */
		*context_handle = (gss_ctx_id_t)spnego_ctx->ctx_handle;
 		if (actual_mech != NULL)
 			*actual_mech = spnego_ctx->actual_mech;
 		if (ret_flags != NULL)
 			*ret_flags = spnego_ctx->ctx_flags;
		release_spnego_ctx(&spnego_ctx);
 	} else if (ret != GSS_S_CONTINUE_NEEDED) {
 		if (spnego_ctx != NULL) {
 			gss_delete_sec_context(&tmpmin,
					       &spnego_ctx->ctx_handle,
					       GSS_C_NO_BUFFER);
			release_spnego_ctx(&spnego_ctx);
		}
		*context_handle = GSS_C_NO_CONTEXT;
	}
	if (mechtok_in != GSS_C_NO_BUFFER) {
		gss_release_buffer(&tmpmin, mechtok_in);
		free(mechtok_in);
	}
	if (mechListMIC_in != GSS_C_NO_BUFFER) {
		gss_release_buffer(&tmpmin, mechListMIC_in);
		free(mechListMIC_in);
	}
	if (mechListMIC_out != GSS_C_NO_BUFFER) {
		gss_release_buffer(&tmpmin, mechListMIC_out);
		free(mechListMIC_out);
	}
	return ret;
} /* init_sec_context */

Vulnerability Type: DoS 
CWE ID: CWE-18
Summary: lib/gssapi/spnego/spnego_mech.c in MIT Kerberos 5 (aka krb5) before 1.14 relies on an inappropriate context handle, which allows remote attackers to cause a denial of service (incorrect pointer read and process crash) via a crafted SPNEGO packet that is mishandled during a gss_inquire_context call.
Commit Message: Fix SPNEGO context aliasing bugs [CVE-2015-2695]

The SPNEGO mechanism currently replaces its context handle with the
mechanism context handle upon establishment, under the assumption that
most GSS functions are only called after context establishment.  This
assumption is incorrect, and can lead to aliasing violations for some
programs.  Maintain the SPNEGO context structure after context
establishment and refer to it in all GSS methods.  Add initiate and
opened flags to the SPNEGO context structure for use in
gss_inquire_context() prior to context establishment.

CVE-2015-2695:

In MIT krb5 1.5 and later, applications which call
gss_inquire_context() on a partially-established SPNEGO context can
cause the GSS-API library to read from a pointer using the wrong type,
generally causing a process crash.  This bug may go unnoticed, because
the most common SPNEGO authentication scenario establishes the context
after just one call to gss_accept_sec_context().  Java server
applications using the native JGSS provider are vulnerable to this
bug.  A carefully crafted SPNEGO packet might allow the
gss_inquire_context() call to succeed with attacker-determined
results, but applications should not make access control decisions
based on gss_inquire_context() results prior to context establishment.

    CVSSv2 Vector: AV:N/AC:M/Au:N/C:N/I:N/A:C/E:POC/RL:OF/RC:C

[ghudson@mit.edu: several bugfixes, style changes, and edge-case
behavior changes; commit message and CVE description]

ticket: 8244
target_version: 1.14
tags: pullup