dcesrv_core: wrap gensec_*() calls in [un]become_root() calls

This is important for the source3/rpc_server code as it might
be called embedded in smbd and may not run as root with access
to our private tdb/ldb files.

Note this is only really needed for 4.15 and older, as
we no longer run the rpc_server embedded in smbd,
but we better be consistent for now.

This should be able to fix the problem the printing no longer works
on Windows 7 with 2021-10 monthly rollup patch (KB5006743).

Windows uses NTLMSSP with privacy at the DCERPC layer on top
of NCACN_NP (smb).

BUG: https://bugzilla.samba.org/show_bug.cgi?id=14867

Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Andreas Schneider <asn@samba.org>
(cherry picked from commit 0651fa474cd68b18d8eb9bdc7c4ba5b847ba9ad9)

3 files changed, 25 insertions, 0 deletions

diff --git a/librpc/rpc/dcesrv_auth.c b/librpc/rpc/dcesrv_auth.c
index fec8df513a8..99d8e016216 100644
--- a/librpc/rpc/dcesrv_auth.c
+++ b/librpc/rpc/dcesrv_auth.c
@@ -130,11 +130,13 @@ static bool dcesrv_auth_prepare_gensec(struct dcesrv_call_state *call)
 	auth->auth_level = call->in_auth_info.auth_level;
 	auth->auth_context_id = call->in_auth_info.auth_context_id;
 
+	cb->auth.become_root();
 	status = cb->auth.gensec_prepare(
 		auth,
 		call,
 		&auth->gensec_security,
 		cb->auth.private_data);
+	cb->auth.unbecome_root();
 	if (!NT_STATUS_IS_OK(status)) {
 		DEBUG(1, ("Failed to call samba_server_gensec_start %s\n",
 			  nt_errstr(status)));
@@ -329,6 +331,7 @@ bool dcesrv_auth_bind(struct dcesrv_call_state *call)
 NTSTATUS dcesrv_auth_complete(struct dcesrv_call_state *call, NTSTATUS status)
 {
 	struct dcesrv_auth *auth = call->auth_state;
+	struct dcesrv_context_callbacks *cb = call->conn->dce_ctx->callbacks;
 	const char *pdu = "<unknown>";
 
 	switch (call->pkt.ptype) {
@@ -359,9 +362,11 @@ NTSTATUS dcesrv_auth_complete(struct dcesrv_call_state *call, NTSTATUS status)
 		return status;
 	}
 
+	cb->auth.become_root();
 	status = gensec_session_info(auth->gensec_security,
 				     auth,
 				     &auth->session_info);
+	cb->auth.unbecome_root();
 	if (!NT_STATUS_IS_OK(status)) {
 		DEBUG(1, ("Failed to establish session_info: %s\n",
 			  nt_errstr(status)));
diff --git a/librpc/rpc/dcesrv_core.c b/librpc/rpc/dcesrv_core.c
index 015c7639a51..9fd71812905 100644
--- a/librpc/rpc/dcesrv_core.c
+++ b/librpc/rpc/dcesrv_core.c
@@ -970,6 +970,7 @@ static NTSTATUS dcesrv_bind(struct dcesrv_call_state *call)
 	struct dcerpc_binding *ep_2nd_description = NULL;
 	const char *endpoint = NULL;
 	struct dcesrv_auth *auth = call->auth_state;
+	struct dcesrv_context_callbacks *cb = call->conn->dce_ctx->callbacks;
 	struct dcerpc_ack_ctx *ack_ctx_list = NULL;
 	struct dcerpc_ack_ctx *ack_features = NULL;
 	struct tevent_req *subreq = NULL;
@@ -1175,9 +1176,11 @@ static NTSTATUS dcesrv_bind(struct dcesrv_call_state *call)
 		return dcesrv_auth_reply(call);
 	}
 
+	cb->auth.become_root();
 	subreq = gensec_update_send(call, call->event_ctx,
 				    auth->gensec_security,
 				    call->in_auth_info.credentials);
+	cb->auth.unbecome_root();
 	if (subreq == NULL) {
 		return NT_STATUS_NO_MEMORY;
 	}
@@ -1192,10 +1195,13 @@ static void dcesrv_bind_done(struct tevent_req *subreq)
 		tevent_req_callback_data(subreq,
 		struct dcesrv_call_state);
 	struct dcesrv_connection *conn = call->conn;
+	struct dcesrv_context_callbacks *cb = call->conn->dce_ctx->callbacks;
 	NTSTATUS status;
 
+	cb->auth.become_root();
 	status = gensec_update_recv(subreq, call,
 				    &call->out_auth_info->credentials);
+	cb->auth.unbecome_root();
 	TALLOC_FREE(subreq);
 
 	status = dcesrv_auth_complete(call, status);
@@ -1253,6 +1259,7 @@ static NTSTATUS dcesrv_auth3(struct dcesrv_call_state *call)
 {
 	struct dcesrv_connection *conn = call->conn;
 	struct dcesrv_auth *auth = call->auth_state;
+	struct dcesrv_context_callbacks *cb = call->conn->dce_ctx->callbacks;
 	struct tevent_req *subreq = NULL;
 	NTSTATUS status;
 
@@ -1297,9 +1304,11 @@ static NTSTATUS dcesrv_auth3(struct dcesrv_call_state *call)
 		return NT_STATUS_OK;
 	}
 
+	cb->auth.become_root();
 	subreq = gensec_update_send(call, call->event_ctx,
 				    auth->gensec_security,
 				    call->in_auth_info.credentials);
+	cb->auth.unbecome_root();
 	if (subreq == NULL) {
 		return NT_STATUS_NO_MEMORY;
 	}
@@ -1315,10 +1324,13 @@ static void dcesrv_auth3_done(struct tevent_req *subreq)
 		struct dcesrv_call_state);
 	struct dcesrv_connection *conn = call->conn;
 	struct dcesrv_auth *auth = call->auth_state;
+	struct dcesrv_context_callbacks *cb = call->conn->dce_ctx->callbacks;
 	NTSTATUS status;
 
+	cb->auth.become_root();
 	status = gensec_update_recv(subreq, call,
 				    &call->out_auth_info->credentials);
+	cb->auth.unbecome_root();
 	TALLOC_FREE(subreq);
 
 	status = dcesrv_auth_complete(call, status);
@@ -1587,6 +1599,7 @@ static NTSTATUS dcesrv_alter(struct dcesrv_call_state *call)
 	struct ncacn_packet *pkt = &call->ack_pkt;
 	uint32_t extra_flags = 0;
 	struct dcesrv_auth *auth = call->auth_state;
+	struct dcesrv_context_callbacks *cb = call->conn->dce_ctx->callbacks;
 	struct dcerpc_ack_ctx *ack_ctx_list = NULL;
 	struct tevent_req *subreq = NULL;
 	size_t i;
@@ -1698,9 +1711,11 @@ static NTSTATUS dcesrv_alter(struct dcesrv_call_state *call)
 		return dcesrv_auth_reply(call);
 	}
 
+	cb->auth.become_root();
 	subreq = gensec_update_send(call, call->event_ctx,
 				    auth->gensec_security,
 				    call->in_auth_info.credentials);
+	cb->auth.unbecome_root();
 	if (subreq == NULL) {
 		return NT_STATUS_NO_MEMORY;
 	}
@@ -1715,10 +1730,13 @@ static void dcesrv_alter_done(struct tevent_req *subreq)
 		tevent_req_callback_data(subreq,
 		struct dcesrv_call_state);
 	struct dcesrv_connection *conn = call->conn;
+	struct dcesrv_context_callbacks *cb = call->conn->dce_ctx->callbacks;
 	NTSTATUS status;
 
+	cb->auth.become_root();
 	status = gensec_update_recv(subreq, call,
 				    &call->out_auth_info->credentials);
+	cb->auth.unbecome_root();
 	TALLOC_FREE(subreq);
 
 	status = dcesrv_auth_complete(call, status);
diff --git a/librpc/rpc/dcesrv_core.h b/librpc/rpc/dcesrv_core.h
index e8e87bcce94..69815b71f3d 100644
--- a/librpc/rpc/dcesrv_core.h
+++ b/librpc/rpc/dcesrv_core.h
@@ -392,6 +392,8 @@ struct dcesrv_context_callbacks {
 			struct gensec_security **out,
 			void *private_data);
 		void *private_data;
+		void (*become_root)(void);
+		void (*unbecome_root)(void);
 	} auth;
 	struct {
 		NTSTATUS (*find)(