cifs: Always resolve hostname before reconnecting

BugLink: https://bugs.launchpad.net/bugs/1837664
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>
Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

diff --git a/fs/cifs/connect.c b/fs/cifs/connect.c
index fc354fd578df2ae076a3a261402d1871a521b7ae..582996fd7e3b15ff5ba666018a2bd2e1c72650d7 100644 (file)
--- a/fs/cifs/connect.c
+++ b/fs/cifs/connect.c
@@ -51,6 +51,7 @@
 #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"
@@ -313,6 +314,53 @@ static void cifs_prune_tlinks(struct work_struct *work);
 static int cifs_setup_volume_info(struct smb_vol *volume_info, char *mount_data,
                                        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
  *
@@ -409,6 +457,11 @@ cifs_reconnect(struct TCP_Server_Info *server)
                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 {