tools: hv: Netlink source address validation allows DoS

The source code without this patch caused hypervkvpd to exit when it processed
a spoofed Netlink packet which has been sent from an untrusted local user.
Now Netlink messages with a non-zero nl_pid source address are ignored
and a warning is printed into the syslog.

Signed-off-by: Tomas Hozza <thozza@redhat.com>
Acked-by:  K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
static void kvp_process_ipconfig_file(char *cmd,
					char *config_buf, int len,
					int element_size, int offset)
{
	char buf[256];
	char *p;
	char *x;
	FILE *file;

	/*
	 * First execute the command.
	 */
	file = popen(cmd, "r");
	if (file == NULL)
		return;

	if (offset == 0)
		memset(config_buf, 0, len);
	while ((p = fgets(buf, sizeof(buf), file)) != NULL) {
		if ((len - strlen(config_buf)) < (element_size + 1))
			break;

		x = strchr(p, '\n');
		*x = '\0';
		strcat(config_buf, p);
		strcat(config_buf, ";");
	}
	pclose(file);
}

static void kvp_process_ipconfig_file(char *cmd,
					char *config_buf, int len,
					int element_size, int offset)
{
	char buf[256];
	char *p;
	char *x;
	FILE *file;

	/*
	 * First execute the command.
	 */
	file = popen(cmd, "r");
	if (file == NULL)
		return;

	if (offset == 0)
		memset(config_buf, 0, len);
	while ((p = fgets(buf, sizeof(buf), file)) != NULL) {
		if ((len - strlen(config_buf)) < (element_size + 1))
			break;

		x = strchr(p, '\n');
		*x = '\0';
		strcat(config_buf, p);
		strcat(config_buf, ";");
	}
	pclose(file);
}
