1 files changed, 88 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..8bf8978bc5d6
--- /dev/null
+++ b/fs/smb/client/dns_resolve.c
@@ -0,0 +1,88 @@
+// 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"
+
+/**
+ * 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.
+ * @expiry: Where to return the expiry time for the dns record.
+ *
+ * Returns zero success, -ve on error.
+ */
+int
+dns_resolve_server_name_to_ip(const char *unc, struct sockaddr *ip_addr, time64_t *expiry)
+{
+	const char *hostname, *sep;
+	char *ip;
+	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(ip_addr, hostname, len);
+	if (rc > 0) {
+		cifs_dbg(FYI, "%s: unc is IP, skipping dns upcall: %*.*s\n", __func__, len, len,
+			 hostname);
+		return 0;
+	}
+
+	/* Perform the upcall */
+	rc = dns_query(current->nsproxy->net_ns, NULL, hostname, len,
+		       NULL, &ip, expiry, false);
+	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 expiry %llu\n",
+			 __func__, len, len, hostname, ip,
+			 expiry ? (*expiry) : 0);
+
+		rc = cifs_convert_address(ip_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;
+}