[PATCH 4.4 52/65] cifs: Always resolve hostname before reconnecting

Greg Kroah-Hartman
2019-02-04T11:08:29Z

From: Paulo Alcantara <paulo@paulo.ac>

commit 28eb24ff75c5ac130eb326b3b4d0dcecfc0f427d upstream.

In case a hostname resolves to a different IP address (e.g. long
running mounts), make sure to resolve it every time prior to calling
generic_ip_connect() in reconnect.

Suggested-by: Steve French <stfrench@microsoft.com>
Signed-off-by: Paulo Alcantara <palcantara@suse.de>
Signed-off-by: Steve French <stfrench@microsoft.com>
Signed-off-by: Pavel Shilovsky <pshilov@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
fs/cifs/connect.c | 53 +++++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 53 insertions(+)

--- a/fs/cifs/connect.c
+++ b/fs/cifs/connect.c
@@ -48,6 +48,7 @@
#include "cifs_unicode.h"
#include "cifs_debug.h"
#include "cifs_fs_sb.h"
+#include "dns_resolve.h"
#include "ntlmssp.h"
#include "nterr.h"
#include "rfc1002pdu.h"
@@ -304,6 +305,53 @@ static int cifs_setup_volume_info(struct
const char *devname);

/*
+ * Resolve hostname and set ip addr in tcp ses. Useful for hostnames that may
+ * get their ip addresses changed at some point.
+ *
+ * This should be called with server->srv_mutex held.
+ */
+#ifdef CONFIG_CIFS_DFS_UPCALL
+static int reconn_set_ipaddr(struct TCP_Server_Info *server)
+{
+ int rc;
+ int len;
+ char *unc, *ipaddr = NULL;
+
+ if (!server->hostname)
+ return -EINVAL;
+
+ len = strlen(server->hostname) + 3;
+
+ unc = kmalloc(len, GFP_KERNEL);
+ if (!unc) {
+ cifs_dbg(FYI, "%s: failed to create UNC path\n", __func__);
+ return -ENOMEM;
+ }
+ snprintf(unc, len, "\\\\%s", server->hostname);
+
+ rc = dns_resolve_server_name_to_ip(unc, &ipaddr);
+ kfree(unc);
+
+ if (rc < 0) {
+ cifs_dbg(FYI, "%s: failed to resolve server part of %s to IP: %d\n",
+ __func__, server->hostname, rc);
+ return rc;
+ }
+
+ rc = cifs_convert_address((struct sockaddr *)&server->dstaddr, ipaddr,
+ strlen(ipaddr));
+ kfree(ipaddr);
+
+ return !rc ? -1 : 0;
+}
+#else
+static inline int reconn_set_ipaddr(struct TCP_Server_Info *server)
+{
+ return 0;
+}
+#endif
+
+/*
* cifs tcp session reconnection
*
* mark tcp session as reconnecting so temporarily locked
@@ -400,6 +448,11 @@ cifs_reconnect(struct TCP_Server_Info *s
rc = generic_ip_connect(server);
if (rc) {
cifs_dbg(FYI, "reconnect error %d\n", rc);
+ rc = reconn_set_ipaddr(server);
+ if (rc) {
+ cifs_dbg(FYI, "%s: failed to resolve hostname: %d\n",
+ __func__, rc);
+ }
mutex_unlock(&server->srv_mutex);
msleep(3000);
} else {