cifs: handle hostnames that resolve to same ip in failover

In order to support reconnect to hostnames that resolve to same ip
address, besides relying on the currently set hostname to match DFS
targets, attempt to resolve the targets and then match their addresses
with the reconnected server ip address.

For instance, if we have two hostnames "FOO" and "BAR", and both
resolve to the same ip address, we would be able to handle failover in
DFS paths like

    \\FOO\dfs\link1 -> [ \BAZ\share2 (*), \BAR\share1 ]
    \\FOO\dfs\link2 -> [ \BAZ\share2 (*), \FOO\share1 ]

so when "BAZ" is no longer accessible, link1 and link2 would get
reconnected despite having different target hostnames.

Signed-off-by: Paulo Alcantara (SUSE) <pc@cjr.nz>
Reviewed-by: Aurelien Aptel <aaptel@suse.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

1 files changed, 38 insertions, 18 deletions

diff --git a/fs/cifs/smb2pdu.c b/fs/cifs/smb2pdu.c
index b30aa3cdd845..cabc19f404e6 100644
--- a/fs/cifs/smb2pdu.c
+++ b/fs/cifs/smb2pdu.c
@@ -160,6 +160,7 @@ static int __smb2_reconnect(const struct nls_table *nlsc,
 			    struct cifs_tcon *tcon)
 {
 	int rc;
+	struct TCP_Server_Info *server = tcon->ses->server;
 	struct dfs_cache_tgt_list tl;
 	struct dfs_cache_tgt_iterator *it = NULL;
 	char *tree;
@@ -172,15 +173,15 @@ static int __smb2_reconnect(const struct nls_table *nlsc,
 	if (!tree)
 		return -ENOMEM;
 
-	if (tcon->ipc) {
-		scnprintf(tree, MAX_TREE_SIZE, "\\\\%s\\IPC$",
-			  tcon->ses->server->hostname);
-		rc = SMB2_tcon(0, tcon->ses, tree, tcon, nlsc);
-		goto out;
-	}
-
 	if (!tcon->dfs_path) {
-		rc = SMB2_tcon(0, tcon->ses, tcon->treeName, tcon, nlsc);
+		if (tcon->ipc) {
+			scnprintf(tree, MAX_TREE_SIZE, "\\\\%s\\IPC$",
+				  server->hostname);
+			rc = SMB2_tcon(0, tcon->ses, tree, tcon, nlsc);
+		} else {
+			rc = SMB2_tcon(0, tcon->ses, tcon->treeName, tcon,
+				       nlsc);
+		}
 		goto out;
 	}
 
@@ -188,13 +189,13 @@ static int __smb2_reconnect(const struct nls_table *nlsc,
 	if (rc)
 		goto out;
 
-	extract_unc_hostname(tcon->ses->server->hostname, &tcp_host,
-			     &tcp_host_len);
+	extract_unc_hostname(server->hostname, &tcp_host, &tcp_host_len);
 
 	for (it = dfs_cache_get_tgt_iterator(&tl); it;
 	     it = dfs_cache_get_next_tgt(&tl, it)) {
 		const char *share, *prefix;
 		size_t share_len, prefix_len;
+		bool target_match;
 
 		rc = dfs_cache_get_tgt_share(it, &share, &share_len, &prefix,
 					     &prefix_len);
@@ -208,19 +209,38 @@ static int __smb2_reconnect(const struct nls_table *nlsc,
 
 		if (dfs_host_len != tcp_host_len
 		    || strncasecmp(dfs_host, tcp_host, dfs_host_len) != 0) {
-			cifs_dbg(FYI, "%s: skipping %.*s, doesn't match %.*s",
+			cifs_dbg(FYI, "%s: %.*s doesn't match %.*s",
 				 __func__,
 				 (int)dfs_host_len, dfs_host,
 				 (int)tcp_host_len, tcp_host);
-			continue;
-		}
 
-		scnprintf(tree, MAX_TREE_SIZE, "\\%.*s", (int)share_len, share);
+			rc = match_target_ip(server, dfs_host, dfs_host_len,
+					     &target_match);
+			if (rc) {
+				cifs_dbg(VFS, "%s: failed to match target ip: %d\n",
+					 __func__, rc);
+				break;
+			}
 
-		rc = SMB2_tcon(0, tcon->ses, tree, tcon, nlsc);
-		if (!rc) {
-			rc = update_super_prepath(tcon, prefix, prefix_len);
-			break;
+			if (!target_match) {
+				cifs_dbg(FYI, "%s: skipping target\n", __func__);
+				continue;
+			}
+		}
+
+		if (tcon->ipc) {
+			scnprintf(tree, MAX_TREE_SIZE, "\\\\%.*s\\IPC$",
+				  (int)share_len, share);
+			rc = SMB2_tcon(0, tcon->ses, tree, tcon, nlsc);
+		} else {
+			scnprintf(tree, MAX_TREE_SIZE, "\\%.*s", (int)share_len,
+				  share);
+			rc = SMB2_tcon(0, tcon->ses, tree, tcon, nlsc);
+			if (!rc) {
+				rc = update_super_prepath(tcon, prefix,
+							  prefix_len);
+				break;
+			}
 		}
 		if (rc == -EREMOTE)
 			break;