Fix GSS-API context leak in TKEY negotiation

Reject multi-round GSS-API negotiation (GSS_S_CONTINUE_NEEDED) in
dst_gssapi_acceptctx().  Each call to gss_accept_sec_context()
allocates a context inside the GSS library; without this fix, the
context handle was passed back to process_gsstkey() which did not
store it persistently, leaking it on every incomplete negotiation.

An unauthenticated attacker could exhaust server memory by sending
repeated TKEY queries with GSSAPI tokens, each leaking one GSS
context.  The leaked memory is allocated by the GSS library via
malloc(), bypassing BIND's memory accounting.

In practice, Kerberos/SPNEGO (the only mechanism used with BIND)
completes in a single round, so rejecting continuation does not
affect real-world deployments.  See RFC 3645 Section 4.1.3.

(cherry picked from commit 3d8e0d068f08694282c5ecd3bd6c332de6c75485)

diff --git a/lib/dns/gssapictx.c b/lib/dns/gssapictx.c
index 60fac791a07df3ae070ae98099ec4447393a8626..a1df18a6afcc80055916d8fa6ead8c94ccb4f54e 100644 (file)
--- a/lib/dns/gssapictx.c
+++ b/lib/dns/gssapictx.c
@@ -604,7 +604,14 @@ dst_gssapi_initctx(const dns_name_t *name, isc_buffer_t *intoken,
                GSS_SPNEGO_MECHANISM, flags, 0, NULL, gintokenp, NULL,
                &gouttoken, &ret_flags, NULL);
 
-       if (gret != GSS_S_COMPLETE && gret != GSS_S_CONTINUE_NEEDED) {
+       switch (gret) {
+       case GSS_S_COMPLETE:
+               result = ISC_R_SUCCESS;
+               break;
+       case GSS_S_CONTINUE_NEEDED:
+               result = DNS_R_CONTINUE;
+               break;
+       default:
                gss_err_message(mctx, gret, minor, err_message);
                if (err_message != NULL && *err_message != NULL) {
                        gss_log(3, "Failure initiating security context: %s",
@@ -629,12 +636,6 @@ dst_gssapi_initctx(const dns_name_t *name, isc_buffer_t *intoken,
                CHECK(isc_buffer_copyregion(outtoken, &r));
        }
 
-       if (gret == GSS_S_COMPLETE) {
-               result = ISC_R_SUCCESS;
-       } else {
-               result = DNS_R_CONTINUE;
-       }
-
 cleanup:
        if (gouttoken.length != 0U) {
                (void)gss_release_buffer(&minor, &gouttoken);
@@ -659,15 +660,10 @@ dst_gssapi_acceptctx(dns_gss_cred_id_t cred, const char *gssapi_keytab,
        char buf[1024];
 
        REQUIRE(outtoken != NULL && *outtoken == NULL);
+       REQUIRE(*ctxout == NULL);
 
        REGION_TO_GBUFFER(*intoken, gintoken);
 
-       if (*ctxout == NULL) {
-               context = GSS_C_NO_CONTEXT;
-       } else {
-               context = *ctxout;
-       }
-
        if (gssapi_keytab != NULL) {
 #if HAVE_GSSAPI_GSSAPI_KRB5_H || HAVE_GSSAPI_KRB5_H
                gret = gsskrb5_register_acceptor_identity(gssapi_keytab);
@@ -712,8 +708,15 @@ dst_gssapi_acceptctx(dns_gss_cred_id_t cred, const char *gssapi_keytab,
 
        switch (gret) {
        case GSS_S_COMPLETE:
-       case GSS_S_CONTINUE_NEEDED:
                break;
+       /*
+        * RFC 3645 4.1.3: we don't handle GSS_S_CONTINUE_NEEDED
+        * Multi-round GSS-API negotiation is not supported.
+        */
+       case GSS_S_CONTINUE_NEEDED:
+               gss_log(3, "multi-round GSS-API negotiation not supported");
+               (void)gss_delete_sec_context(&minor, &context, NULL);
+               FALLTHROUGH;
        case GSS_S_DEFECTIVE_TOKEN:
        case GSS_S_DEFECTIVE_CREDENTIAL:
        case GSS_S_BAD_SIG:
@@ -726,7 +729,7 @@ dst_gssapi_acceptctx(dns_gss_cred_id_t cred, const char *gssapi_keytab,
        case GSS_S_BAD_MECH:
        case GSS_S_FAILURE:
                result = DNS_R_INVALIDTKEY;
-       /* fall through */
+               FALLTHROUGH;
        default:
                gss_log(3, "failed gss_accept_sec_context: %s",
                        gss_error_tostring(gret, minor, buf, sizeof(buf)));
@@ -744,43 +747,44 @@ dst_gssapi_acceptctx(dns_gss_cred_id_t cred, const char *gssapi_keytab,
                (void)gss_release_buffer(&minor, &gouttoken);
        }
 
-       if (gret == GSS_S_COMPLETE) {
-               gret = gss_display_name(&minor, gname, &gnamebuf, NULL);
-               if (gret != GSS_S_COMPLETE) {
-                       gss_log(3, "failed gss_display_name: %s",
-                               gss_error_tostring(gret, minor, buf,
-                                                  sizeof(buf)));
-                       CHECK(ISC_R_FAILURE);
-               }
+       INSIST(gret == GSS_S_COMPLETE);
 
-               /*
-                * Compensate for a bug in Solaris8's implementation
-                * of gss_display_name().  Should be harmless in any
-                * case, since principal names really should not
-                * contain null characters.
-                */
-               if (gnamebuf.length > 0U &&
-                   ((char *)gnamebuf.value)[gnamebuf.length - 1] == '\0')
-               {
-                       gnamebuf.length--;
-               }
+       gret = gss_display_name(&minor, gname, &gnamebuf, NULL);
+       if (gret != GSS_S_COMPLETE) {
+               gss_log(3, "failed gss_display_name: %s",
+                       gss_error_tostring(gret, minor, buf, sizeof(buf)));
+               result = ISC_R_FAILURE;
+               goto cleanup;
+       }
 
-               gss_log(3, "gss-api source name (accept) is %.*s",
-                       (int)gnamebuf.length, (char *)gnamebuf.value);
+       /*
+        * Compensate for a bug in Solaris8's implementation
+        * of gss_display_name().  Should be harmless in any
+        * case, since principal names really should not
+        * contain null characters.
+        */
+       if (gnamebuf.length > 0U &&
+           ((char *)gnamebuf.value)[gnamebuf.length - 1] == '\0')
+       {
+               gnamebuf.length--;
+       }
 
-               GBUFFER_TO_REGION(gnamebuf, r);
-               isc_buffer_init(&namebuf, r.base, r.length);
-               isc_buffer_add(&namebuf, r.length);
+       gss_log(3, "gss-api source name (accept) is %.*s", (int)gnamebuf.length,
+               (char *)gnamebuf.value);
 
-               CHECK(dns_name_fromtext(principal, &namebuf, dns_rootname, 0,
-                                       NULL));
-       } else {
-               result = DNS_R_CONTINUE;
-       }
+       GBUFFER_TO_REGION(gnamebuf, r);
+       isc_buffer_init(&namebuf, r.base, r.length);
+       isc_buffer_add(&namebuf, r.length);
+
+       CHECK(dns_name_fromtext(principal, &namebuf, dns_rootname, 0, NULL));
 
        *ctxout = context;
 
 cleanup:
+       if (result != ISC_R_SUCCESS && context != GSS_C_NO_CONTEXT) {
+               (void)gss_delete_sec_context(&minor, &context, NULL);
+       }
+
        if (gnamebuf.length != 0U) {
                gret = gss_release_buffer(&minor, &gnamebuf);
                if (gret != GSS_S_COMPLETE) {

diff --git a/lib/dns/include/dst/gssapi.h b/lib/dns/include/dst/gssapi.h
index 494b4b0762ba8dd8a30b7ef74517f5b8c49bd186..5945bf7637a3e98dc0929eaceefbf675b4fc8402 100644 (file)
--- a/lib/dns/include/dst/gssapi.h
+++ b/lib/dns/include/dst/gssapi.h
@@ -113,20 +113,17 @@ dst_gssapi_acceptctx(dns_gss_cred_id_t cred, const char *gssapi_keytab,
  *                generated by gss_accept_sec_context() to be sent to the
  *                initiator
  *      'context'  is a valid pointer to receive the generated context handle.
- *                 On the initial call, it should be a pointer to NULL, which
- *                will be allocated as a dns_gss_ctx_id_t.  Subsequent calls
- *                should pass in the handle generated on the first call.
- *                Call dst_gssapi_releasecred to delete the context and free
- *                the memory.
  *
  *     Requires:
- *             'outtoken' to != NULL && *outtoken == NULL.
+ *             'outtoken' != NULL && *outtoken == NULL.
+ *             'context'  != NULL && *context  == NULL.
  *
  *     Returns:
- *             ISC_R_SUCCESS   msg was successfully updated to include the
- *                             query to be sent
- *             DNS_R_CONTINUE  transaction still in progress
- *             other           an error occurred while building the message
+ *             ISC_R_SUCCESS           msg was successfully updated to include
+ *                                     the query to be sent
+ *             DNS_R_INVALIDTKEY       an error occurred while accepting the
+ *                                     context
+ *             ISC_R_FAILURE           other error occurred
  */
 
 isc_result_t

diff --git a/lib/dns/tkey.c b/lib/dns/tkey.c
index 8aa4c076d3155aec94196ee8f00e46c68cadd4b9..a78dc83f03a09992a3e75c0d8b38ae9e43f36cc9 100644 (file)
--- a/lib/dns/tkey.c
+++ b/lib/dns/tkey.c
@@ -528,19 +528,9 @@ process_gsstkey(dns_message_t *msg, dns_name_t *name, dns_rdata_tkey_t *tkeyin,
                return ISC_R_SUCCESS;
        }
 
-       /*
-        * XXXDCL need to check for key expiry per 4.1.1
-        * XXXDCL need a way to check fully established, perhaps w/key_flags
-        */
-
        intoken.base = tkeyin->key;
        intoken.length = tkeyin->keylen;
 
-       result = dns_tsigkey_find(&tsigkey, name, &tkeyin->algorithm, ring);
-       if (result == ISC_R_SUCCESS) {
-               gss_ctx = dst_key_getgssctx(tsigkey->key);
-       }
-
        principal = dns_fixedname_initname(&fixed);
 
        /*
@@ -549,7 +539,7 @@ process_gsstkey(dns_message_t *msg, dns_name_t *name, dns_rdata_tkey_t *tkeyin,
        result = dst_gssapi_acceptctx(tctx->gsscred, tctx->gssapi_keytab,
                                      &intoken, &outtoken, &gss_ctx, principal,
                                      tctx->mctx);
-       if (result == DNS_R_INVALIDTKEY) {
+       if (result != ISC_R_SUCCESS) {
                if (tsigkey != NULL) {
                        dns_tsigkey_detach(&tsigkey);
                }
@@ -558,11 +548,11 @@ process_gsstkey(dns_message_t *msg, dns_name_t *name, dns_rdata_tkey_t *tkeyin,
                                                                      */
                return ISC_R_SUCCESS;
        }
-       if (result != DNS_R_CONTINUE && result != ISC_R_SUCCESS) {
-               CHECK(result);
-       }
+
        /*
-        * XXXDCL Section 4.1.3: Limit GSS_S_CONTINUE_NEEDED to 10 times.
+        * Multi-round GSS-API negotiation (GSS_S_CONTINUE_NEEDED) is
+        * rejected in dst_gssapi_acceptctx(), so if we reach here the
+        * negotiation is complete and the principal must be set.
         */
 
        isc_stdtime_get(&now);
@@ -633,6 +623,9 @@ process_gsstkey(dns_message_t *msg, dns_name_t *name, dns_rdata_tkey_t *tkeyin,
        return ISC_R_SUCCESS;
 
 cleanup:
+       if (dstkey == NULL && gss_ctx != NULL) {
+               dst_gssapi_deletectx(tctx->mctx, &gss_ctx);
+       }
        if (tsigkey != NULL) {
                dns_tsigkey_detach(&tsigkey);
        }
@@ -1546,9 +1539,8 @@ dns_tkey_gssnegotiate(dns_message_t *qmsg, dns_message_t *rmsg,
                                 NULL));
 
        /*
-        * XXXSRA This seems confused.  If we got CONTINUE from initctx,
-        * the GSS negotiation hasn't completed yet, so we can't sign
-        * anything yet.
+        * GSS negotiation is complete (CONTINUE returned earlier).
+        * Create the TSIG key from the established context.
         */
 
        CHECK(dns_tsigkey_createfromkey(