From: Michal Privoznik <mprivozn@redhat.com> The usual flow of SASL is REMOTE_PROC_AUTH_SASL_INIT followed by REMOTE_PROC_AUTH_SASL_START which can either complete authentication or require further steps which are then done by calling REMOTE_PROC_AUTH_SASL_STEP (multiple times even). But if a malicious client skips the SASL_START step and calls SASL_INIT followed by SASL_STEP then the 'sasl->conn' structure inside of virNetSASLSessionServerStep() is not fully allocated (most notably the list of auth mechanisms 'mech' is NULL). But then sasl_server_step() dereferences that pointer leading to a crash. Fix this by disallowing SASL_STEP until SASL_START completed successfully. Fixes: CVE-2026-119151 Resolves: https://gitlab.com/libvirt/libvirt/-/work_items/940 Signed-off-by: Michal Privoznik <mprivozn@redhat.com> --- v2 of: https://lists.libvirt.org/archives/list/devel@lists.libvirt.org/thread/3R2JC... diff to v1: - Implement a state machine to allow just INIT -> START [-> STEP [-> STEP ...]] and nothing else, - Drop checks additional from remote_daemon_dispatch.c (they were only there to report a nicer error message anyways). src/remote/remote_daemon_dispatch.c | 2 +- src/rpc/virnetsaslcontext.c | 31 +++++++++++++++++++++++++++++ 2 files changed, 32 insertions(+), 1 deletion(-) diff --git a/src/remote/remote_daemon_dispatch.c b/src/remote/remote_daemon_dispatch.c index e548438250..2f1861f5bb 100644 --- a/src/remote/remote_daemon_dispatch.c +++ b/src/remote/remote_daemon_dispatch.c @@ -4034,7 +4034,7 @@ remoteDispatchAuthSaslStep(virNetServer *server, VIR_DEBUG("Step SASL auth %d", virNetServerClientGetFD(client)); if (virNetServerClientGetAuth(client) != VIR_NET_SERVER_SERVICE_AUTH_SASL || priv->sasl == NULL) { - VIR_ERROR(_("client tried invalid SASL start request")); + VIR_ERROR(_("client tried invalid SASL step request")); goto authfail; } diff --git a/src/rpc/virnetsaslcontext.c b/src/rpc/virnetsaslcontext.c index 8692703117..325ebd915e 100644 --- a/src/rpc/virnetsaslcontext.c +++ b/src/rpc/virnetsaslcontext.c @@ -37,12 +37,20 @@ struct _virNetSASLContext { unsigned int tcpMinSSF; }; +typedef enum virNetSASLSessionState virNetSASLSessionState; +enum virNetSASLSessionState { + VIR_NET_SASL_SESSION_STATE_INIT, + VIR_NET_SASL_SESSION_STATE_START, + VIR_NET_SASL_SESSION_STATE_STEP +}; + struct _virNetSASLSession { virObjectLockable parent; sasl_conn_t *conn; size_t maxbufsize; sasl_callback_t *callbacks; + virNetSASLSessionState state; }; @@ -248,6 +256,8 @@ virNetSASLSession *virNetSASLSessionNewServer(virNetSASLContext *ctxt G_GNUC_UNU goto cleanup; } + sasl->state = VIR_NET_SASL_SESSION_STATE_INIT; + return sasl; cleanup: @@ -529,6 +539,13 @@ int virNetSASLSessionServerStart(virNetSASLSession *sasl, int ret = -1; virObjectLock(sasl); + + if (sasl->state != VIR_NET_SASL_SESSION_STATE_INIT) { + virReportError(VIR_ERR_AUTH_FAILED, "%s", + _("unexpected state of SASL session")); + goto cleanup; + } + err = sasl_server_start(sasl->conn, mechname, clientin, @@ -542,12 +559,15 @@ int virNetSASLSessionServerStart(virNetSASLSession *sasl, case SASL_OK: if (virNetSASLSessionUpdateBufSize(sasl) < 0) goto cleanup; + sasl->state = VIR_NET_SASL_SESSION_STATE_START; ret = VIR_NET_SASL_COMPLETE; break; case SASL_CONTINUE: + sasl->state = VIR_NET_SASL_SESSION_STATE_START; ret = VIR_NET_SASL_CONTINUE; break; case SASL_INTERACT: + sasl->state = VIR_NET_SASL_SESSION_STATE_START; ret = VIR_NET_SASL_INTERACT; break; default: @@ -575,6 +595,14 @@ int virNetSASLSessionServerStep(virNetSASLSession *sasl, int ret = -1; virObjectLock(sasl); + + if (sasl->state != VIR_NET_SASL_SESSION_STATE_START && + sasl->state != VIR_NET_SASL_SESSION_STATE_STEP) { + virReportError(VIR_ERR_AUTH_FAILED, "%s", + _("unexpected state of SASL session")); + goto cleanup; + } + err = sasl_server_step(sasl->conn, clientin, inlen, @@ -587,12 +615,15 @@ int virNetSASLSessionServerStep(virNetSASLSession *sasl, case SASL_OK: if (virNetSASLSessionUpdateBufSize(sasl) < 0) goto cleanup; + sasl->state = VIR_NET_SASL_SESSION_STATE_STEP; ret = VIR_NET_SASL_COMPLETE; break; case SASL_CONTINUE: + sasl->state = VIR_NET_SASL_SESSION_STATE_STEP; ret = VIR_NET_SASL_CONTINUE; break; case SASL_INTERACT: + sasl->state = VIR_NET_SASL_SESSION_STATE_STEP; ret = VIR_NET_SASL_INTERACT; break; default: -- 2.56.0