1 files changed, 96 insertions, 0 deletions
diff --git a/fs/smb/client/dns_resolve.c b/fs/smb/client/dns_resolve.c
new file mode 100644
index 000000000000..de7f4b384718
--- /dev/null
+++ b/fs/smb/client/dns_resolve.c
@@ -0,0 +1,96 @@
+// SPDX-License-Identifier: LGPL-2.1
+/*
+ *
+ *   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.
+ *
+ */
+
+#include <linux/inet.h>
+#include <linux/slab.h>
+#include <linux/dns_resolver.h>
+#include "dns_resolve.h"
+#include "cifsglob.h"
+#include "cifsproto.h"
+#include "cifs_debug.h"
+
+static int resolve_name(const char *name, size_t namelen, struct sockaddr *addr)
+{
+	char *ip;
+	int rc;
+
+	rc = dns_query(current->nsproxy->net_ns, NULL, name,
+		       namelen, NULL, &ip, NULL, false);
+	if (rc < 0) {
+		cifs_dbg(FYI, "%s: unable to resolve: %*.*s\n",
+			 __func__, (int)namelen, (int)namelen, name);
+	} else {
+		cifs_dbg(FYI, "%s: resolved: %*.*s to %s\n",
+			 __func__, (int)namelen, (int)namelen, name, ip);
+
+		rc = cifs_convert_address(addr, ip, strlen(ip));
+		kfree(ip);
+		if (!rc) {
+			cifs_dbg(FYI, "%s: unable to determine ip address\n",
+				 __func__);
+			rc = -EHOSTUNREACH;
+		} else {
+			rc = 0;
+		}
+	}
+	return rc;
+}
+
+/**
+ * dns_resolve_name - Perform an upcall to resolve hostname to an ip address.
+ * @dom: DNS domain name (or NULL)
+ * @name: Name to look up
+ * @namelen: Length of name
+ * @ip_addr: Where to return the IP address
+ *
+ * Returns zero on success, -ve code otherwise.
+ */
+int dns_resolve_name(const char *dom, const char *name,
+		     size_t namelen, struct sockaddr *ip_addr)
+{
+	size_t len;
+	char *s;
+	int rc;
+
+	cifs_dbg(FYI, "%s: dom=%s name=%.*s\n", __func__, dom, (int)namelen, name);
+	if (!ip_addr || !name || !*name || !namelen)
+		return -EINVAL;
+
+	cifs_dbg(FYI, "%s: hostname=%.*s\n", __func__, (int)namelen, name);
+	/* Try to interpret hostname as an IPv4 or IPv6 address */
+	rc = cifs_convert_address(ip_addr, name, namelen);
+	if (rc > 0) {
+		cifs_dbg(FYI, "%s: unc is IP, skipping dns upcall: %*.*s\n",
+			 __func__, (int)namelen, (int)namelen, name);
+		return 0;
+	}
+
+	/*
+	 * If @name contains a NetBIOS name and @dom has been specified, then
+	 * convert @name to an FQDN and try resolving it first.
+	 */
+	if (dom && *dom && cifs_netbios_name(name, namelen)) {
+		len = strnlen(dom, CIFS_MAX_DOMAINNAME_LEN) + namelen + 2;
+		s = kmalloc(len, GFP_KERNEL);
+		if (!s)
+			return -ENOMEM;
+
+		scnprintf(s, len, "%.*s.%s", (int)namelen, name, dom);
+		rc = resolve_name(s, len - 1, ip_addr);
+		kfree(s);
+		if (!rc)
+			return 0;
+	}
+	return resolve_name(name, namelen, ip_addr);
+}