s3-printing: follow force user/group for driver IO

Configuring force user/group settings for the print$ share currently has
unexpected results, this is explained by how the driver upload/add
process takes place. Consider the following example:

[print$]
        path = /print-drv
        write list = $DRIVER_UPLOAD_USER
        force group = ntadmin

- the client connects to the [print$] share and uploads all driver
  files to the /print-drv/W32X86 directory.

- This is permitted, as /print-drv/W32X86 is owned by group ntadmin, and
  the "force group = ntadmin" takes effect for the [print$] session.

- Once all files are uploaded, the client connects to the [ipc$]
  share and issues an AddPrinterDriverEx spoolss request.

- In handling this request move_driver_to_download_area() is called,
  which attempts to create the directory /print-drv/W32X86/3

- The create directory fails, as it is done as the user connected to
  the [ipc$] share which does not have permission to write to the driver
  directory. The [print$] "force group = ntadmin" has no effect.

This is a regression from previous behaviour prior to the commit:
783ab04 Convert move_driver_to_download_area to use create_conn_struct.

https://bugzilla.samba.org/show_bug.cgi?id=7921
Signed-off-by: Andreas Schneider <asn@samba.org>

3 files changed, 118 insertions, 57 deletions

diff --git a/source3/include/proto.h b/source3/include/proto.h
index e866dedc60..199ee4836c 100644
--- a/source3/include/proto.h
+++ b/source3/include/proto.h
@@ -5150,6 +5150,7 @@ void exit_server_fault(void);
 /* The following definitions come from smbd/service.c  */
 
 bool set_conn_connectpath(connection_struct *conn, const char *connectpath);
+NTSTATUS set_conn_force_user_group(connection_struct *conn, int snum);
 bool set_current_service(connection_struct *conn, uint16 flags, bool do_chdir);
 void load_registry_shares(void);
 int add_home_service(const char *service, const char *username, const char *homedir);
diff --git a/source3/printing/nt_printing.c b/source3/printing/nt_printing.c
index d77320cf02..1d075e794e 100644
--- a/source3/printing/nt_printing.c
+++ b/source3/printing/nt_printing.c
@@ -625,6 +625,19 @@ static uint32 get_correct_cversion(struct pipes_struct *p,
 		return -1;
 	}
 
+	nt_status = set_conn_force_user_group(conn, printdollar_snum);
+	if (!NT_STATUS_IS_OK(nt_status)) {
+		DEBUG(0, ("failed set force user / group\n"));
+		*perr = ntstatus_to_werror(nt_status);
+		goto error_free_conn;
+	}
+
+	if (!become_user(conn, get_current_vuid(conn))) {
+		DEBUG(0, ("failed to become user\n"));
+		*perr = WERR_ACCESS_DENIED;
+		goto error_free_conn;
+	}
+
 	/* Open the driver file (Portable Executable format) and determine the
 	 * deriver the cversion. */
 	driverpath = talloc_asprintf(talloc_tos(),
@@ -720,6 +733,8 @@ static uint32 get_correct_cversion(struct pipes_struct *p,
 	*perr = WERR_OK;
 
  error_exit:
+	unbecome_user();
+ error_free_conn:
 	TALLOC_FREE(smb_fname);
 	if (fsp != NULL) {
 		close_file(NULL, fsp, NORMAL_CLOSE);
@@ -993,6 +1008,19 @@ WERROR move_driver_to_download_area(struct pipes_struct *p,
 		return err;
 	}
 
+	nt_status = set_conn_force_user_group(conn, printdollar_snum);
+	if (!NT_STATUS_IS_OK(nt_status)) {
+		DEBUG(0, ("failed set force user / group\n"));
+		err = ntstatus_to_werror(nt_status);
+		goto err_free_conn;
+	}
+
+	if (!become_user(conn, get_current_vuid(conn))) {
+		DEBUG(0, ("failed to become user\n"));
+		err = WERR_ACCESS_DENIED;
+		goto err_free_conn;
+	}
+
 	new_dir = talloc_asprintf(ctx,
 				"%s/%d",
 				short_architecture,
@@ -1126,7 +1154,9 @@ WERROR move_driver_to_download_area(struct pipes_struct *p,
 	}
 
 	err = WERR_OK;
-  err_exit:
+ err_exit:
+	unbecome_user();
+ err_free_conn:
 	TALLOC_FREE(smb_dname);
 
 	if (conn != NULL) {
@@ -1907,6 +1937,19 @@ bool delete_driver_files(const struct auth_serversupplied_info *session_info,
 		return false;
 	}
 
+	nt_status = set_conn_force_user_group(conn, printdollar_snum);
+	if (!NT_STATUS_IS_OK(nt_status)) {
+		DEBUG(0, ("failed set force user / group\n"));
+		ret = false;
+		goto err_free_conn;
+	}
+
+	if (!become_user(conn, get_current_vuid(conn))) {
+		DEBUG(0, ("failed to become user\n"));
+		ret = false;
+		goto err_free_conn;
+	}
+
 	if ( !CAN_WRITE(conn) ) {
 		DEBUG(3,("delete_driver_files: Cannot delete print driver when [print$] is read-only\n"));
 		ret = false;
@@ -1968,6 +2011,8 @@ bool delete_driver_files(const struct auth_serversupplied_info *session_info,
 
 	ret = true;
  err_out:
+	unbecome_user();
+ err_free_conn:
 	if (conn != NULL) {
 		vfs_ChDir(conn, oldcwd);
 		SMB_VFS_DISCONNECT(conn);
diff --git a/source3/smbd/service.c b/source3/smbd/service.c
index e713b7132e..00b5294be6 100644
--- a/source3/smbd/service.c
+++ b/source3/smbd/service.c
@@ -659,6 +659,72 @@ static NTSTATUS create_connection_session_info(struct smbd_server_connection *sc
 	return NT_STATUS_ACCESS_DENIED;
 }
 
+/****************************************************************************
+  set relavent user and group settings corresponding to force user/group
+  configuration for the given snum.
+****************************************************************************/
+
+NTSTATUS set_conn_force_user_group(connection_struct *conn, int snum)
+{
+	NTSTATUS status;
+
+	if (*lp_force_user(snum)) {
+
+		/*
+		 * Replace conn->session_info with a completely faked up one
+		 * from the username we are forced into :-)
+		 */
+
+		char *fuser;
+		struct auth_serversupplied_info *forced_serverinfo;
+
+		fuser = talloc_string_sub(conn, lp_force_user(snum), "%S",
+					  lp_const_servicename(snum));
+		if (fuser == NULL) {
+			return NT_STATUS_NO_MEMORY;
+		}
+
+		status = make_serverinfo_from_username(
+			conn, fuser, conn->session_info->guest,
+			&forced_serverinfo);
+		if (!NT_STATUS_IS_OK(status)) {
+			return status;
+		}
+
+		TALLOC_FREE(conn->session_info);
+		conn->session_info = forced_serverinfo;
+
+		conn->force_user = true;
+		DEBUG(3,("Forced user %s\n", fuser));
+	}
+
+	/*
+	 * If force group is true, then override
+	 * any groupid stored for the connecting user.
+	 */
+
+	if (*lp_force_group(snum)) {
+
+		status = find_forced_group(
+			conn->force_user, snum, conn->session_info->unix_name,
+			&conn->session_info->security_token->sids[1],
+			&conn->session_info->utok.gid);
+
+		if (!NT_STATUS_IS_OK(status)) {
+			return status;
+		}
+
+		/*
+		 * We need to cache this gid, to use within
+		 * change_to_user() separately from the conn->session_info
+		 * struct. We only use conn->session_info directly if
+		 * "force_user" was set.
+		 */
+		conn->force_group_gid = conn->session_info->utok.gid;
+	}
+
+	return NT_STATUS_OK;
+}
 
 /****************************************************************************
   Make a connection, given the snum to connect to, and the vuser of the
@@ -742,62 +808,11 @@ connection_struct *make_connection_snum(struct smbd_server_connection *sconn,
 
 	conn->read_only = lp_readonly(SNUM(conn));
 
-	if (*lp_force_user(snum)) {
-
-		/*
-		 * Replace conn->session_info with a completely faked up one
-		 * from the username we are forced into :-)
-		 */
-
-		char *fuser;
-		struct auth_serversupplied_info *forced_serverinfo;
-
-		fuser = talloc_string_sub(conn, lp_force_user(snum), "%S",
-					  lp_servicename(snum));
-		if (fuser == NULL) {
-			*pstatus = NT_STATUS_NO_MEMORY;
-			goto err_root_exit;
-		}
-
-		status = make_serverinfo_from_username(
-			conn, fuser, conn->session_info->guest,
-			&forced_serverinfo);
-		if (!NT_STATUS_IS_OK(status)) {
-			*pstatus = status;
-			goto err_root_exit;
-		}
-
-		TALLOC_FREE(conn->session_info);
-		conn->session_info = forced_serverinfo;
-
-		conn->force_user = True;
-		DEBUG(3,("Forced user %s\n", fuser));
-	}
-
-	/*
-	 * If force group is true, then override
-	 * any groupid stored for the connecting user.
-	 */
-
-	if (*lp_force_group(snum)) {
-
-		status = find_forced_group(
-			conn->force_user, snum, conn->session_info->unix_name,
-			&conn->session_info->security_token->sids[1],
-			&conn->session_info->utok.gid);
-
-		if (!NT_STATUS_IS_OK(status)) {
-			*pstatus = status;
-			goto err_root_exit;
-		}
-
-		/*
-		 * We need to cache this gid, to use within
-		 * change_to_user() separately from the conn->session_info
-		 * struct. We only use conn->session_info directly if
- 		 * "force_user" was set.
- 		 */
-		conn->force_group_gid = conn->session_info->utok.gid;
+	status = set_conn_force_user_group(conn, snum);
+	if (!NT_STATUS_IS_OK(status)) {
+		conn_free(conn);
+		*pstatus = status;
+		return NULL;
 	}
 
 	conn->vuid = (vuser != NULL) ? vuser->vuid : UID_FIELD_INVALID;