v4.19.13 snapshot.
diff --git a/fs/cifs/dns_resolve.c b/fs/cifs/dns_resolve.c
new file mode 100644
index 0000000..7ede730
--- /dev/null
+++ b/fs/cifs/dns_resolve.c
@@ -0,0 +1,99 @@
+/*
+ * fs/cifs/dns_resolve.c
+ *
+ * Copyright (c) 2007 Igor Mammedov
+ * Author(s): Igor Mammedov (niallain@gmail.com)
+ * Steve French (sfrench@us.ibm.com)
+ * Wang Lei (wang840925@gmail.com)
+ * David Howells (dhowells@redhat.com)
+ *
+ * Contains the CIFS DFS upcall routines used for hostname to
+ * IP address translation.
+ *
+ * This library is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published
+ * by the Free Software Foundation; either version 2.1 of the License, or
+ * (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See
+ * the GNU Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this library; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
+ */
+
+#include <linux/slab.h>
+#include <linux/dns_resolver.h>
+#include "dns_resolve.h"
+#include "cifsglob.h"
+#include "cifsproto.h"
+#include "cifs_debug.h"
+
+/**
+ * dns_resolve_server_name_to_ip - Resolve UNC server name to ip address.
+ * @unc: UNC path specifying the server (with '/' as delimiter)
+ * @ip_addr: Where to return the IP address.
+ *
+ * The IP address will be returned in string form, and the caller is
+ * responsible for freeing it.
+ *
+ * Returns length of result on success, -ve on error.
+ */
+int
+dns_resolve_server_name_to_ip(const char *unc, char **ip_addr)
+{
+ struct sockaddr_storage ss;
+ const char *hostname, *sep;
+ char *name;
+ int len, rc;
+
+ if (!ip_addr || !unc)
+ return -EINVAL;
+
+ len = strlen(unc);
+ if (len < 3) {
+ cifs_dbg(FYI, "%s: unc is too short: %s\n", __func__, unc);
+ return -EINVAL;
+ }
+
+ /* Discount leading slashes for cifs */
+ len -= 2;
+ hostname = unc + 2;
+
+ /* Search for server name delimiter */
+ sep = memchr(hostname, '/', len);
+ if (sep)
+ len = sep - hostname;
+ else
+ cifs_dbg(FYI, "%s: probably server name is whole unc: %s\n",
+ __func__, unc);
+
+ /* Try to interpret hostname as an IPv4 or IPv6 address */
+ rc = cifs_convert_address((struct sockaddr *)&ss, hostname, len);
+ if (rc > 0)
+ goto name_is_IP_address;
+
+ /* Perform the upcall */
+ rc = dns_query(NULL, hostname, len, NULL, ip_addr, NULL);
+ if (rc < 0)
+ cifs_dbg(FYI, "%s: unable to resolve: %*.*s\n",
+ __func__, len, len, hostname);
+ else
+ cifs_dbg(FYI, "%s: resolved: %*.*s to %s\n",
+ __func__, len, len, hostname, *ip_addr);
+ return rc;
+
+name_is_IP_address:
+ name = kmalloc(len + 1, GFP_KERNEL);
+ if (!name)
+ return -ENOMEM;
+ memcpy(name, hostname, len);
+ name[len] = 0;
+ cifs_dbg(FYI, "%s: unc is IP, skipping dns upcall: %s\n",
+ __func__, name);
+ *ip_addr = name;
+ return 0;
+}