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 3883058bf284de2889e4e3676767e58ad91a0ae3)

diff --git a/lib/dns/gssapictx.c b/lib/dns/gssapictx.c
index f2a64e897993a7d1d580674c16692688003bc24a..c7bc5d1810def25579884c4c8f6fcc2a49954e76 100644 (file)
--- a/lib/dns/gssapictx.c
+++ b/lib/dns/gssapictx.c
@@ -608,7 +608,14 @@ 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",
@@ -634,12 +641,6 @@ dst_gssapi_initctx(const dns_name_t *name, isc_buffer_t *intoken,
                RETERR(isc_buffer_copyregion(outtoken, &r));
        }
 
-       if (gret == GSS_S_COMPLETE) {
-               result = ISC_R_SUCCESS;
-       } else {
-               result = DNS_R_CONTINUE;
-       }
-
 out:
        if (gouttoken.length != 0U) {
                (void)gss_release_buffer(&minor, &gouttoken);
@@ -664,15 +665,10 @@ 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 defined(ISC_PLATFORM_GSSAPI_KRB5_HEADER) || defined(WIN32)
                gret = gsskrb5_register_acceptor_identity(gssapi_keytab);
@@ -717,8 +713,15 @@ 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:
@@ -731,7 +734,7 @@ 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)));
@@ -749,52 +752,56 @@ 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)));
-                       RETERR(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 out;
+       }
 
-               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);
 
-               RETERR(dns_name_fromtext(principal, &namebuf, dns_rootname, 0,
-                                        NULL));
+       GBUFFER_TO_REGION(gnamebuf, r);
+       isc_buffer_init(&namebuf, r.base, r.length);
+       isc_buffer_add(&namebuf, r.length);
 
-               if (gnamebuf.length != 0U) {
-                       gret = gss_release_buffer(&minor, &gnamebuf);
-                       if (gret != GSS_S_COMPLETE) {
-                               gss_log(3, "failed gss_release_buffer: %s",
-                                       gss_error_tostring(gret, minor, buf,
-                                                          sizeof(buf)));
-                       }
-               }
-       } else {
-               result = DNS_R_CONTINUE;
+       result = dns_name_fromtext(principal, &namebuf, dns_rootname, 0, NULL);
+       if (result != ISC_R_SUCCESS) {
+               goto out;
        }
 
        *ctxout = context;
 
 out:
+       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) {
+                       gss_log(3, "failed gss_release_buffer: %s",
+                               gss_error_tostring(gret, minor, buf,
+                                                  sizeof(buf)));
+               }
+       }
+
        if (gname != NULL) {
                gret = gss_release_name(&minor, &gname);
                if (gret != GSS_S_COMPLETE) {

diff --git a/lib/dns/include/dst/gssapi.h b/lib/dns/include/dst/gssapi.h
index e783f20bd3de450a77ac870e35f43bebd20850be..c325c4b097ecd891a0f53c13b3f9d4fb6865c1f8 100644 (file)
--- a/lib/dns/include/dst/gssapi.h
+++ b/lib/dns/include/dst/gssapi.h
@@ -115,20 +115,17 @@ 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 d91ed3123b7afccf340f374c8a612394f35397b6..7f39fbdd31722c2f3e481d71bd78c55ecaa1ecef 100644 (file)
--- a/lib/dns/tkey.c
+++ b/lib/dns/tkey.c
@@ -534,19 +534,9 @@ 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);
 
        /*
@@ -555,7 +545,7 @@ 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);
                }
@@ -564,11 +554,11 @@ 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) {
-               goto failure;
-       }
+
        /*
-        * 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);
@@ -639,6 +629,10 @@ process_gsstkey(dns_message_t *msg, dns_name_t *name, dns_rdata_tkey_t *tkeyin,
        return (ISC_R_SUCCESS);
 
 failure:
+       if (dstkey == NULL && gss_ctx != NULL) {
+               dst_gssapi_deletectx(tctx->mctx, &gss_ctx);
+       }
+
        if (tsigkey != NULL) {
                dns_tsigkey_detach(&tsigkey);
        }
@@ -1576,9 +1570,8 @@ 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.
         */
 
        RETERR(dns_tsigkey_createfromkey(