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, 48 insertions, 0 deletions

diff --git a/fs/cifs/misc.c b/fs/cifs/misc.c
index 550ce9020a3e..1ec6a5543eda 100644
--- a/fs/cifs/misc.c
+++ b/fs/cifs/misc.c
@@ -32,6 +32,9 @@
 #include "cifs_unicode.h"
 #include "smb2pdu.h"
 #include "cifsfs.h"
+#ifdef CONFIG_CIFS_DFS_UPCALL
+#include "dns_resolve.h"
+#endif
 
 extern mempool_t *cifs_sm_req_poolp;
 extern mempool_t *cifs_req_poolp;
@@ -1083,6 +1086,51 @@ void cifs_put_tcp_super(struct super_block *sb)
 }
 
 #ifdef CONFIG_CIFS_DFS_UPCALL
+int match_target_ip(struct TCP_Server_Info *server,
+		    const char *share, size_t share_len,
+		    bool *result)
+{
+	int rc;
+	char *target, *tip = NULL;
+	struct sockaddr tipaddr;
+
+	*result = false;
+
+	target = kzalloc(share_len + 3, GFP_KERNEL);
+	if (!target) {
+		rc = -ENOMEM;
+		goto out;
+	}
+
+	scnprintf(target, share_len + 3, "\\\\%.*s", (int)share_len, share);
+
+	cifs_dbg(FYI, "%s: target name: %s\n", __func__, target + 2);
+
+	rc = dns_resolve_server_name_to_ip(target, &tip);
+	if (rc < 0)
+		goto out;
+
+	cifs_dbg(FYI, "%s: target ip: %s\n", __func__, tip);
+
+	if (!cifs_convert_address(&tipaddr, tip, strlen(tip))) {
+		cifs_dbg(VFS, "%s: failed to convert target ip address\n",
+			 __func__);
+		rc = -EINVAL;
+		goto out;
+	}
+
+	*result = cifs_match_ipaddr((struct sockaddr *)&server->dstaddr,
+				    &tipaddr);
+	cifs_dbg(FYI, "%s: ip addresses match: %u\n", __func__, *result);
+	rc = 0;
+
+out:
+	kfree(target);
+	kfree(tip);
+
+	return rc;
+}
+
 static void tcon_super_cb(struct super_block *sb, void *arg)
 {
 	struct super_cb_data *sd = arg;