From: Ondřej Surý Date: Tue, 17 Mar 2026 23:10:35 +0000 (+0100) Subject: Fix GSS-API context leak in TKEY negotiation X-Git-Tag: v9.21.22~7^2~2 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=51dde6ef431c4290f7fa0a0a45670e1d67c6f195;p=thirdparty%2Fbind9.git 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. --- diff --git a/lib/dns/gssapictx.c b/lib/dns/gssapictx.c index b500e94cdaa..bbfebb9accc 100644 --- a/lib/dns/gssapictx.c +++ b/lib/dns/gssapictx.c @@ -336,7 +336,14 @@ 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", @@ -361,12 +368,6 @@ 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); @@ -390,15 +391,10 @@ dst_gssapi_acceptctx(const char *gssapi_keytab, isc_region_t *intoken, 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); @@ -442,8 +438,15 @@ dst_gssapi_acceptctx(const char *gssapi_keytab, isc_region_t *intoken, 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: @@ -456,7 +459,7 @@ dst_gssapi_acceptctx(const char *gssapi_keytab, isc_region_t *intoken, 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))); @@ -474,42 +477,43 @@ dst_gssapi_acceptctx(const char *gssapi_keytab, isc_region_t *intoken, (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))); - CLEANUP(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))); + CLEANUP(ISC_R_FAILURE); + } - 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)); - } 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)); *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 a519487da00..6551e014cef 100644 --- a/lib/dns/include/dst/gssapi.h +++ b/lib/dns/include/dst/gssapi.h @@ -71,18 +71,17 @@ dst_gssapi_acceptctx(const char *gssapi_keytab, isc_region_t *intoken, * 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. * * 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 a65661670f1..38bdbd3ad74 100644 --- a/lib/dns/tkey.c +++ b/lib/dns/tkey.c @@ -181,7 +181,7 @@ process_gsstkey(dns_message_t *msg, dns_name_t *name, dns_rdata_tkey_t *tkeyin, intoken = (isc_region_t){ tkeyin->key, tkeyin->keylen }; result = dst_gssapi_acceptctx(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); } @@ -189,12 +189,11 @@ process_gsstkey(dns_message_t *msg, dns_name_t *name, dns_rdata_tkey_t *tkeyin, tkey_log("process_gsstkey(): dns_tsigerror_badkey"); 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. */ if (dns_name_countlabels(principal) == 0U) { if (tsigkey != NULL) { @@ -678,9 +677,8 @@ 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(tkeyname, DST_ALG_GSSAPI, dstkey, true, false, NULL, rtkey.inception,