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 char *kvp_mac_to_if_name(char *mac)
{
	DIR *dir;
	struct dirent *entry;
	FILE    *file;
	char    *p, *q, *x;
	char    *if_name = NULL;
	char    buf[256];
	char *kvp_net_dir = "/sys/class/net/";
	char dev_id[256];
	int i;

	dir = opendir(kvp_net_dir);
	if (dir == NULL)
		return NULL;

	snprintf(dev_id, sizeof(dev_id), kvp_net_dir);
	q = dev_id + strlen(kvp_net_dir);

	while ((entry = readdir(dir)) != NULL) {
		/*
		 * Set the state for the next pass.
		 */
		*q = '\0';

		strcat(dev_id, entry->d_name);
		strcat(dev_id, "/address");

		file = fopen(dev_id, "r");
		if (file == NULL)
			continue;

		p = fgets(buf, sizeof(buf), file);
		if (p) {
			x = strchr(p, '\n');
			if (x)
				*x = '\0';

			for (i = 0; i < strlen(p); i++)
				p[i] = toupper(p[i]);

			if (!strcmp(p, mac)) {
				/*
				 * Found the MAC match; return the interface
				 * name. The caller will free the memory.
				 */
				if_name = strdup(entry->d_name);
				fclose(file);
				break;
			}
		}
		fclose(file);
	}

	closedir(dir);
	return if_name;
}

static char *kvp_mac_to_if_name(char *mac)
{
	DIR *dir;
	struct dirent *entry;
	FILE    *file;
	char    *p, *q, *x;
	char    *if_name = NULL;
	char    buf[256];
	char *kvp_net_dir = "/sys/class/net/";
	char dev_id[256];
	int i;

	dir = opendir(kvp_net_dir);
	if (dir == NULL)
		return NULL;

	snprintf(dev_id, sizeof(dev_id), kvp_net_dir);
	q = dev_id + strlen(kvp_net_dir);

	while ((entry = readdir(dir)) != NULL) {
		/*
		 * Set the state for the next pass.
		 */
		*q = '\0';

		strcat(dev_id, entry->d_name);
		strcat(dev_id, "/address");

		file = fopen(dev_id, "r");
		if (file == NULL)
			continue;

		p = fgets(buf, sizeof(buf), file);
		if (p) {
			x = strchr(p, '\n');
			if (x)
				*x = '\0';

			for (i = 0; i < strlen(p); i++)
				p[i] = toupper(p[i]);

			if (!strcmp(p, mac)) {
				/*
				 * Found the MAC match; return the interface
				 * name. The caller will free the memory.
				 */
				if_name = strdup(entry->d_name);
				fclose(file);
				break;
			}
		}
		fclose(file);
	}

	closedir(dir);
	return if_name;
}
