[PATCH 3/3] cifs: On cifs_reconnect, resolve the hostname again.

[Tim Gardner]

From: Shyam Prasad N <sprasad at microsoft.com>

BugLink: https://canonical.my.salesforce.com/5004K000005pQNG

On cifs_reconnect, make sure that DNS resolution happens again.
It could be the cause of connection to go dead in the first place.

This also contains the fix for a build issue identified by Intel bot.
Reported-by: kernel test robot <lkp at intel.com>

Signed-off-by: Shyam Prasad N <sprasad at microsoft.com>
Reviewed-by: Paulo Alcantara (SUSE) <pc at cjr.nz>
Reviewed-by: Pavel Shilovsky <pshilov at microsoft.com>
CC: <stable at vger.kernel.org> # 5.11+
Signed-off-by: Steve French <stfrench at microsoft.com>
(backported from commit 4e456b30f78c429b183db420e23b26cde7e03a78)
[rtg - context adjustment]
Signed-off-by: Tim Gardner <tim.gardner at canonical.com>
---
 fs/cifs/Kconfig   |  3 +--
 fs/cifs/Makefile  |  5 +++--
 fs/cifs/connect.c | 27 ++++++++++++++++++++-------
 3 files changed, 24 insertions(+), 11 deletions(-)

diff --git a/fs/cifs/Kconfig b/fs/cifs/Kconfig
index 22cf04fb32d35..16e2d2ef96bb0 100644
--- a/fs/cifs/Kconfig
+++ b/fs/cifs/Kconfig
@@ -18,6 +18,7 @@ config CIFS
 	select CRYPTO_AES
 	select CRYPTO_LIB_DES
 	select KEYS
+	select DNS_RESOLVER
 	help
 	  This is the client VFS module for the SMB3 family of NAS protocols,
 	  (including support for the most recent, most secure dialect SMB3.1.1)
@@ -112,7 +113,6 @@ config CIFS_WEAK_PW_HASH
 config CIFS_UPCALL
 	bool "Kerberos/SPNEGO advanced session setup"
 	depends on CIFS
-	select DNS_RESOLVER
 	help
 	  Enables an upcall mechanism for CIFS which accesses userspace helper
 	  utilities to provide SPNEGO packaged (RFC 4178) Kerberos tickets
@@ -179,7 +179,6 @@ config CIFS_DEBUG_DUMP_KEYS
 config CIFS_DFS_UPCALL
 	bool "DFS feature support"
 	depends on CIFS
-	select DNS_RESOLVER
 	help
 	  Distributed File System (DFS) support is used to access shares
 	  transparently in an enterprise name space, even if the share
diff --git a/fs/cifs/Makefile b/fs/cifs/Makefile
index 51bae9340842f..523fc419af8ad 100644
--- a/fs/cifs/Makefile
+++ b/fs/cifs/Makefile
@@ -10,13 +10,14 @@ cifs-y := trace.o cifsfs.o cifssmb.o cifs_debug.o connect.o dir.o file.o \
 	  cifs_unicode.o nterr.o cifsencrypt.o \
 	  readdir.o ioctl.o sess.o export.o smb1ops.o winucase.o \
 	  smb2ops.o smb2maperror.o smb2transport.o \
-	  smb2misc.o smb2pdu.o smb2inode.o smb2file.o cifsacl.o
+	  smb2misc.o smb2pdu.o smb2inode.o smb2file.o cifsacl.o \
+	  dns_resolve.o
 
 cifs-$(CONFIG_CIFS_XATTR) += xattr.o
 
 cifs-$(CONFIG_CIFS_UPCALL) += cifs_spnego.o
 
-cifs-$(CONFIG_CIFS_DFS_UPCALL) += dns_resolve.o cifs_dfs_ref.o dfs_cache.o
+cifs-$(CONFIG_CIFS_DFS_UPCALL) += cifs_dfs_ref.o dfs_cache.o
 
 cifs-$(CONFIG_CIFS_FSCACHE) += fscache.o cache.o
 
diff --git a/fs/cifs/connect.c b/fs/cifs/connect.c
index e096751a73873..e2fb0e087a9ee 100644
--- a/fs/cifs/connect.c
+++ b/fs/cifs/connect.c
@@ -343,7 +343,6 @@ static char *extract_hostname(const char *unc);
  *
  * This should be called with server->srv_mutex held.
  */
-#ifdef CONFIG_CIFS_DFS_UPCALL
 static int reconn_set_ipaddr_from_hostname(struct TCP_Server_Info *server)
 {
 	int rc;
@@ -615,12 +614,26 @@ cifs_reconnect(struct TCP_Server_Info *server)
 
 		mutex_lock(&server->srv_mutex);
 #ifdef CONFIG_CIFS_DFS_UPCALL
-		/*
-		 * Set up next DFS target server (if any) for reconnect. If DFS
-		 * feature is disabled, then we will retry last server we
-		 * connected to before.
-		 */
-		reconn_set_next_dfs_target(server, cifs_sb, &tgt_list, &tgt_it);
+		if (cifs_sb && cifs_sb->origin_fullpath)
+			/*
+			 * Set up next DFS target server (if any) for reconnect. If DFS
+			 * feature is disabled, then we will retry last server we
+			 * connected to before.
+			 */
+			reconn_set_next_dfs_target(server, cifs_sb, &tgt_list, &tgt_it);
+		else {
+#endif
+			/*
+			 * Resolve the hostname again to make sure that IP address is up-to-date.
+			 */
+			rc = reconn_set_ipaddr_from_hostname(server);
+			if (rc) {
+				cifs_dbg(FYI, "%s: failed to resolve hostname: %d\n",
+						__func__, rc);
+			}
+
+#ifdef CONFIG_CIFS_DFS_UPCALL
+		}
 #endif
 
 		if (cifs_rdma_enabled(server))
-- 
2.17.1