cifs: support share failover when remounting

When remouting a DFS share, force a new DFS referral of the path and
if the currently cached targets do not match any of the new targets or
there was no cached targets, then mark it for reconnect.

For example:

    $ mount //dom/dfs/link /mnt -o username=foo,password=bar
    $ ls /mnt
    oldfile.txt

    change target share of 'link' in server settings

    $ mount /mnt -o remount,username=foo,password=bar
    $ ls /mnt
    newfile.txt

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

fs/cifs/connect.c

@@ -220,7 +220,7 @@ cifs_reconnect(struct TCP_Server_Info *server)
 #ifdef CONFIG_CIFS_DFS_UPCALL
 	struct super_block *sb = NULL;
 	struct cifs_sb_info *cifs_sb = NULL;
-	struct dfs_cache_tgt_list tgt_list = {0};
+	struct dfs_cache_tgt_list tgt_list = DFS_CACHE_TGT_LIST_INIT(tgt_list);
 	struct dfs_cache_tgt_iterator *tgt_it = NULL;
 #endif
 
@@ -3130,7 +3130,7 @@ static int do_dfs_failover(const char *path, const char *full_path, struct cifs_
 {
 	int rc;
 	char *npath = NULL;
-	struct dfs_cache_tgt_list tgt_list = {0};
+	struct dfs_cache_tgt_list tgt_list = DFS_CACHE_TGT_LIST_INIT(tgt_list);
 	struct dfs_cache_tgt_iterator *tgt_it = NULL;
 	struct smb3_fs_context tmp_ctx = {NULL};
 

fs/cifs/dfs_cache.c

@@ -19,6 +19,7 @@
 #include "cifs_debug.h"
 #include "cifs_unicode.h"
 #include "smb2glob.h"
+#include "dns_resolve.h"
 
 #include "dfs_cache.h"
 
@@ -911,6 +912,7 @@ static int get_targets(struct cache_entry *ce, struct dfs_cache_tgt_list *tl)
 
 err_free_it:
 	list_for_each_entry_safe(it, nit, head, it_list) {
+		list_del(&it->it_list);
 		kfree(it->it_name);
 		kfree(it);
 	}
@@ -1293,6 +1295,194 @@ int dfs_cache_get_tgt_share(char *path, const struct dfs_cache_tgt_iterator *it,
 	return 0;
 }
 
+static bool target_share_equal(struct TCP_Server_Info *server, const char *s1, const char *s2)
+{
+	char unc[sizeof("\\\\") + SERVER_NAME_LENGTH] = {0};
+	const char *host;
+	size_t hostlen;
+	char *ip = NULL;
+	struct sockaddr sa;
+	bool match;
+	int rc;
+
+	if (strcasecmp(s1, s2))
+		return false;
+
+	/*
+	 * Resolve share's hostname and check if server address matches.  Otherwise just ignore it
+	 * as we could not have upcall to resolve hostname or failed to convert ip address.
+	 */
+	match = true;
+	extract_unc_hostname(s1, &host, &hostlen);
+	scnprintf(unc, sizeof(unc), "\\\\%.*s", (int)hostlen, host);
+
+	rc = dns_resolve_server_name_to_ip(unc, &ip, NULL);
+	if (rc < 0) {
+		cifs_dbg(FYI, "%s: could not resolve %.*s. assuming server address matches.\n",
+			 __func__, (int)hostlen, host);
+		return true;
+	}
+
+	if (!cifs_convert_address(&sa, ip, strlen(ip))) {
+		cifs_dbg(VFS, "%s: failed to convert address \'%s\'. skip address matching.\n",
+			 __func__, ip);
+	} else {
+		mutex_lock(&server->srv_mutex);
+		match = cifs_match_ipaddr((struct sockaddr *)&server->dstaddr, &sa);
+		mutex_unlock(&server->srv_mutex);
+	}
+
+	kfree(ip);
+	return match;
+}
+
+/*
+ * Mark dfs tcon for reconnecting when the currently connected tcon does not match any of the new
+ * target shares in @refs.
+ */
+static void mark_for_reconnect_if_needed(struct cifs_tcon *tcon, struct dfs_cache_tgt_list *tl,
+					 const struct dfs_info3_param *refs, int numrefs)
+{
+	struct dfs_cache_tgt_iterator *it;
+	int i;
+
+	for (it = dfs_cache_get_tgt_iterator(tl); it; it = dfs_cache_get_next_tgt(tl, it)) {
+		for (i = 0; i < numrefs; i++) {
+			if (target_share_equal(tcon->ses->server, dfs_cache_get_tgt_name(it),
+					       refs[i].node_name))
+				return;
+		}
+	}
+
+	cifs_dbg(FYI, "%s: no cached or matched targets. mark dfs share for reconnect.\n", __func__);
+	for (i = 0; i < tcon->ses->chan_count; i++) {
+		spin_lock(&GlobalMid_Lock);
+		if (tcon->ses->chans[i].server->tcpStatus != CifsExiting)
+			tcon->ses->chans[i].server->tcpStatus = CifsNeedReconnect;
+		spin_unlock(&GlobalMid_Lock);
+	}
+}
+
+/* Refresh dfs referral of tcon and mark it for reconnect if needed */
+static int refresh_tcon(struct cifs_ses **sessions, struct cifs_tcon *tcon, bool force_refresh)
+{
+	const char *path = tcon->dfs_path + 1;
+	struct cifs_ses *ses;
+	struct cache_entry *ce;
+	struct dfs_info3_param *refs = NULL;
+	int numrefs = 0;
+	bool needs_refresh = false;
+	struct dfs_cache_tgt_list tl = DFS_CACHE_TGT_LIST_INIT(tl);
+	int rc = 0;
+	unsigned int xid;
+
+	ses = find_ipc_from_server_path(sessions, path);
+	if (IS_ERR(ses)) {
+		cifs_dbg(FYI, "%s: could not find ipc session\n", __func__);
+		return PTR_ERR(ses);
+	}
+
+	down_read(&htable_rw_lock);
+	ce = lookup_cache_entry(path);
+	needs_refresh = force_refresh || IS_ERR(ce) || cache_entry_expired(ce);
+	if (!IS_ERR(ce)) {
+		rc = get_targets(ce, &tl);
+		if (rc)
+			cifs_dbg(FYI, "%s: could not get dfs targets: %d\n", __func__, rc);
+	}
+	up_read(&htable_rw_lock);
+
+	if (!needs_refresh) {
+		rc = 0;
+		goto out;
+	}
+
+	xid = get_xid();
+	rc = get_dfs_referral(xid, ses, path, &refs, &numrefs);
+	free_xid(xid);
+
+	/* Create or update a cache entry with the new referral */
+	if (!rc) {
+		dump_refs(refs, numrefs);
+
+		down_write(&htable_rw_lock);
+		ce = lookup_cache_entry(path);
+		if (IS_ERR(ce))
+			add_cache_entry_locked(refs, numrefs);
+		else if (force_refresh || cache_entry_expired(ce))
+			update_cache_entry_locked(ce, refs, numrefs);
+		up_write(&htable_rw_lock);
+
+		mark_for_reconnect_if_needed(tcon, &tl, refs, numrefs);
+	}
+
+out:
+	dfs_cache_free_tgts(&tl);
+	free_dfs_info_array(refs, numrefs);
+	return rc;
+}
+
+/**
+ * dfs_cache_remount_fs - remount a DFS share
+ *
+ * Reconfigure dfs mount by forcing a new DFS referral and if the currently cached targets do not
+ * match any of the new targets, mark it for reconnect.
+ *
+ * @cifs_sb: cifs superblock.
+ *
+ * Return zero if remounted, otherwise non-zero.
+ */
+int dfs_cache_remount_fs(struct cifs_sb_info *cifs_sb)
+{
+	struct cifs_tcon *tcon;
+	struct mount_group *mg;
+	struct cifs_ses *sessions[CACHE_MAX_ENTRIES + 1] = {NULL};
+	int rc;
+
+	if (!cifs_sb || !cifs_sb->master_tlink)
+		return -EINVAL;
+
+	tcon = cifs_sb_master_tcon(cifs_sb);
+	if (!tcon->dfs_path) {
+		cifs_dbg(FYI, "%s: not a dfs tcon\n", __func__);
+		return 0;
+	}
+
+	if (uuid_is_null(&cifs_sb->dfs_mount_id)) {
+		cifs_dbg(FYI, "%s: tcon has no dfs mount group id\n", __func__);
+		return -EINVAL;
+	}
+
+	mutex_lock(&mount_group_list_lock);
+	mg = find_mount_group_locked(&cifs_sb->dfs_mount_id);
+	if (IS_ERR(mg)) {
+		mutex_unlock(&mount_group_list_lock);
+		cifs_dbg(FYI, "%s: tcon has ipc session to refresh referral\n", __func__);
+		return PTR_ERR(mg);
+	}
+	kref_get(&mg->refcount);
+	mutex_unlock(&mount_group_list_lock);
+
+	spin_lock(&mg->lock);
+	memcpy(&sessions, mg->sessions, mg->num_sessions * sizeof(mg->sessions[0]));
+	spin_unlock(&mg->lock);
+
+	/*
+	 * After reconnecting to a different server, unique ids won't match anymore, so we disable
+	 * serverino. This prevents dentry revalidation to think the dentry are stale (ESTALE).
+	 */
+	cifs_autodisable_serverino(cifs_sb);
+	/*
+	 * Force the use of prefix path to support failover on DFS paths that resolve to targets
+	 * that have different prefix paths.
+	 */
+	cifs_sb->mnt_cifs_flags |= CIFS_MOUNT_USE_PREFIX_PATH;
+	rc = refresh_tcon(sessions, tcon, true);
+
+	kref_put(&mg->refcount, mount_group_release);
+	return rc;
+}
+
 /*
  * Refresh all active dfs mounts regardless of whether they are in cache or not.
  * (cache can be cleared)
@@ -1303,7 +1493,6 @@ static void refresh_mounts(struct cifs_ses **sessions)
 	struct cifs_ses *ses;
 	struct cifs_tcon *tcon, *ntcon;
 	struct list_head tcons;
-	unsigned int xid;
 
 	INIT_LIST_HEAD(&tcons);
 
@@ -1321,44 +1510,8 @@ static void refresh_mounts(struct cifs_ses **sessions)
 	spin_unlock(&cifs_tcp_ses_lock);
 
 	list_for_each_entry_safe(tcon, ntcon, &tcons, ulist) {
-		const char *path = tcon->dfs_path + 1;
-		struct cache_entry *ce;
-		struct dfs_info3_param *refs = NULL;
-		int numrefs = 0;
-		bool needs_refresh = false;
-		int rc = 0;
-
 		list_del_init(&tcon->ulist);
-
-		ses = find_ipc_from_server_path(sessions, path);
-		if (IS_ERR(ses))
-			goto next_tcon;
-
-		down_read(&htable_rw_lock);
-		ce = lookup_cache_entry(path);
-		needs_refresh = IS_ERR(ce) || cache_entry_expired(ce);
-		up_read(&htable_rw_lock);
-
-		if (!needs_refresh)
-			goto next_tcon;
-
-		xid = get_xid();
-		rc = get_dfs_referral(xid, ses, path, &refs, &numrefs);
-		free_xid(xid);
-
-		/* Create or update a cache entry with the new referral */
-		if (!rc) {
-			down_write(&htable_rw_lock);
-			ce = lookup_cache_entry(path);
-			if (IS_ERR(ce))
-				add_cache_entry_locked(refs, numrefs);
-			else if (cache_entry_expired(ce))
-				update_cache_entry_locked(ce, refs, numrefs);
-			up_write(&htable_rw_lock);
-		}
-
-next_tcon:
-		free_dfs_info_array(refs, numrefs);
+		refresh_tcon(sessions, tcon, false);
 		cifs_put_tcon(tcon);
 	}
 }

fs/cifs/dfs_cache.h

@@ -13,6 +13,8 @@
 #include <linux/uuid.h>
 #include "cifsglob.h"
 
+#define DFS_CACHE_TGT_LIST_INIT(var) { .tl_numtgts = 0, .tl_list = LIST_HEAD_INIT((var).tl_list), }
+
 struct dfs_cache_tgt_list {
 	int tl_numtgts;
 	struct list_head tl_list;
@@ -44,6 +46,7 @@ int dfs_cache_get_tgt_share(char *path, const struct dfs_cache_tgt_iterator *it,
 void dfs_cache_put_refsrv_sessions(const uuid_t *mount_id);
 void dfs_cache_add_refsrv_session(const uuid_t *mount_id, struct cifs_ses *ses);
 char *dfs_cache_canonical_path(const char *path, const struct nls_table *cp, int remap);
+int dfs_cache_remount_fs(struct cifs_sb_info *cifs_sb);
 
 static inline struct dfs_cache_tgt_iterator *
 dfs_cache_get_next_tgt(struct dfs_cache_tgt_list *tl,

fs/cifs/fs_context.c

@@ -13,6 +13,9 @@
 #include <linux/magic.h>
 #include <linux/security.h>
 #include <net/net_namespace.h>
+#ifdef CONFIG_CIFS_DFS_UPCALL
+#include "dfs_cache.h"
+#endif
 */
 
 #include <linux/ctype.h>
@@ -779,6 +782,10 @@ static int smb3_reconfigure(struct fs_context *fc)
 	smb3_cleanup_fs_context_contents(cifs_sb->ctx);
 	rc = smb3_fs_context_dup(cifs_sb->ctx, ctx);
 	smb3_update_mnt_flags(cifs_sb);
+#ifdef CONFIG_CIFS_DFS_UPCALL
+	if (!rc)
+		rc = dfs_cache_remount_fs(cifs_sb);
+#endif
 
 	return rc;
 }