cifs: handle prefix paths in reconnect

For the case where we have a DFS path like below and we're currently
connected to targetA:

    //dfsroot/link -> //targetA/share/foo, //targetB/share/bar

after failover, we should make sure to update cifs_sb->prepath so the
next operations will use the new prefix path "/bar".

Besides, in order to simplify the use of different prefix paths,
enforce CIFS_MOUNT_USE_PREFIX_PATH for DFS mounts so we don't have to
revalidate the root dentry every time we set a new prefix path.
Signed-off-by: Paulo Alcantara (SUSE) <pc@cjr.nz>
Acked-by: Ronnie Sahlberg <lsahlber@redhat.com>
Reviewed-by: Aurelien Aptel <aaptel@suse.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/cifs/cifsproto.h

@@ -602,6 +602,11 @@ int smb2_parse_query_directory(struct cifs_tcon *tcon, struct kvec *rsp_iov,
 			       int resp_buftype,
 			       struct cifs_search_info *srch_inf);
 
+struct super_block *cifs_get_tcp_super(struct TCP_Server_Info *server);
+void cifs_put_tcp_super(struct super_block *sb);
+int update_super_prepath(struct cifs_tcon *tcon, const char *prefix,
+			 size_t prefix_len);
+
 #ifdef CONFIG_CIFS_DFS_UPCALL
 static inline int get_dfs_path(const unsigned int xid, struct cifs_ses *ses,
 			       const char *old_path,

fs/cifs/cifssmb.c

@@ -162,9 +162,18 @@ static int __cifs_reconnect_tcon(const struct nls_table *nlsc,
 
 	for (it = dfs_cache_get_tgt_iterator(&tl); it;
 	     it = dfs_cache_get_next_tgt(&tl, it)) {
-		const char *tgt = dfs_cache_get_tgt_name(it);
+		const char *share, *prefix;
+		size_t share_len, prefix_len;
 
-		extract_unc_hostname(tgt, &dfs_host, &dfs_host_len);
+		rc = dfs_cache_get_tgt_share(it, &share, &share_len, &prefix,
+					     &prefix_len);
+		if (rc) {
+			cifs_dbg(VFS, "%s: failed to parse target share %d\n",
+				 __func__, rc);
+			continue;
+		}
+
+		extract_unc_hostname(share, &dfs_host, &dfs_host_len);
 
 		if (dfs_host_len != tcp_host_len
 		    || strncasecmp(dfs_host, tcp_host, dfs_host_len) != 0) {
@@ -175,11 +184,13 @@ static int __cifs_reconnect_tcon(const struct nls_table *nlsc,
 			continue;
 		}
 
-		scnprintf(tree, MAX_TREE_SIZE, "\\%s", tgt);
+		scnprintf(tree, MAX_TREE_SIZE, "\\%.*s", (int)share_len, share);
 
 		rc = CIFSTCon(0, tcon->ses, tree, tcon, nlsc);
-		if (!rc)
+		if (!rc) {
+			rc = update_super_prepath(tcon, prefix, prefix_len);
 			break;
+		}
 		if (rc == -EREMOTE)
 			break;
 	}

fs/cifs/connect.c

@@ -57,7 +57,6 @@
 #include "smb2proto.h"
 #include "smbdirect.h"
 #include "dns_resolve.h"
-#include "cifsfs.h"
 #ifdef CONFIG_CIFS_DFS_UPCALL
 #include "dfs_cache.h"
 #endif
@@ -389,54 +388,7 @@ static inline int reconn_set_ipaddr(struct TCP_Server_Info *server)
 #endif
 
 #ifdef CONFIG_CIFS_DFS_UPCALL
-struct super_cb_data {
-	struct TCP_Server_Info *server;
-	struct super_block *sb;
-};
-
 /* These functions must be called with server->srv_mutex held */
-
-static void super_cb(struct super_block *sb, void *arg)
-{
-	struct super_cb_data *d = arg;
-	struct cifs_sb_info *cifs_sb;
-	struct cifs_tcon *tcon;
-
-	if (d->sb)
-		return;
-
-	cifs_sb = CIFS_SB(sb);
-	tcon = cifs_sb_master_tcon(cifs_sb);
-	if (tcon->ses->server == d->server)
-		d->sb = sb;
-}
-
-static struct super_block *get_tcp_super(struct TCP_Server_Info *server)
-{
-	struct super_cb_data d = {
-		.server = server,
-		.sb = NULL,
-	};
-
-	iterate_supers_type(&cifs_fs_type, super_cb, &d);
-
-	if (unlikely(!d.sb))
-		return ERR_PTR(-ENOENT);
-	/*
-	 * Grab an active reference in order to prevent automounts (DFS links)
-	 * of expiring and then freeing up our cifs superblock pointer while
-	 * we're doing failover.
-	 */
-	cifs_sb_active(d.sb);
-	return d.sb;
-}
-
-static inline void put_tcp_super(struct super_block *sb)
-{
-	if (!IS_ERR_OR_NULL(sb))
-		cifs_sb_deactive(sb);
-}
-
 static void reconn_inval_dfs_target(struct TCP_Server_Info *server,
 				    struct cifs_sb_info *cifs_sb,
 				    struct dfs_cache_tgt_list *tgt_list,
@@ -508,7 +460,7 @@ cifs_reconnect(struct TCP_Server_Info *server)
 	server->nr_targets = 1;
 #ifdef CONFIG_CIFS_DFS_UPCALL
 	spin_unlock(&GlobalMid_Lock);
-	sb = get_tcp_super(server);
+	sb = cifs_get_tcp_super(server);
 	if (IS_ERR(sb)) {
 		rc = PTR_ERR(sb);
 		cifs_dbg(FYI, "%s: will not do DFS failover: rc = %d\n",
@@ -535,7 +487,7 @@ cifs_reconnect(struct TCP_Server_Info *server)
 		spin_unlock(&GlobalMid_Lock);
 #ifdef CONFIG_CIFS_DFS_UPCALL
 		dfs_cache_free_tgts(&tgt_list);
-		put_tcp_super(sb);
+		cifs_put_tcp_super(sb);
 #endif
 		return rc;
 	} else
@@ -666,7 +618,7 @@ cifs_reconnect(struct TCP_Server_Info *server)
 
 	}
 
-	put_tcp_super(sb);
+	cifs_put_tcp_super(sb);
 #endif
 	if (server->tcpStatus == CifsNeedNegotiate)
 		mod_delayed_work(cifsiod_wq, &server->echo, 0);
@@ -4999,6 +4951,15 @@ int cifs_mount(struct cifs_sb_info *cifs_sb, struct smb_vol *vol)
 	 * 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;
+	kfree(cifs_sb->prepath);
+	cifs_sb->prepath = vol->prepath;
+	vol->prepath = NULL;
+
 out:
 	free_xid(xid);
 	cifs_try_adding_channels(ses);

fs/cifs/dfs_cache.c

@@ -1260,6 +1260,44 @@ void dfs_cache_del_vol(const char *fullpath)
 	kref_put(&vi->refcnt, vol_release);
 }
 
+/**
+ * dfs_cache_get_tgt_share - parse a DFS target
+ *
+ * @it: DFS target iterator.
+ * @share: tree name.
+ * @share_len: length of tree name.
+ * @prefix: prefix path.
+ * @prefix_len: length of prefix path.
+ *
+ * Return zero if target was parsed correctly, otherwise non-zero.
+ */
+int dfs_cache_get_tgt_share(const struct dfs_cache_tgt_iterator *it,
+			    const char **share, size_t *share_len,
+			    const char **prefix, size_t *prefix_len)
+{
+	char *s, sep;
+
+	if (!it || !share || !share_len || !prefix || !prefix_len)
+		return -EINVAL;
+
+	sep = it->it_name[0];
+	if (sep != '\\' && sep != '/')
+		return -EINVAL;
+
+	s = strchr(it->it_name + 1, sep);
+	if (!s)
+		return -EINVAL;
+
+	s = strchrnul(s + 1, sep);
+
+	*share = it->it_name;
+	*share_len = s - it->it_name;
+	*prefix = *s ? s + 1 : s;
+	*prefix_len = &it->it_name[strlen(it->it_name)] - *prefix;
+
+	return 0;
+}
+
 /* Get all tcons that are within a DFS namespace and can be refreshed */
 static void get_tcons(struct TCP_Server_Info *server, struct list_head *head)
 {

fs/cifs/dfs_cache.h

@@ -49,6 +49,10 @@ extern int dfs_cache_update_vol(const char *fullpath,
 				struct TCP_Server_Info *server);
 extern void dfs_cache_del_vol(const char *fullpath);
 
+extern int dfs_cache_get_tgt_share(const struct dfs_cache_tgt_iterator *it,
+				   const char **share, size_t *share_len,
+				   const char **prefix, size_t *prefix_len);
+
 static inline struct dfs_cache_tgt_iterator *
 dfs_cache_get_next_tgt(struct dfs_cache_tgt_list *tl,
 		       struct dfs_cache_tgt_iterator *it)

fs/cifs/misc.c

@@ -31,6 +31,7 @@
 #include "nterr.h"
 #include "cifs_unicode.h"
 #include "smb2pdu.h"
+#include "cifsfs.h"
 
 extern mempool_t *cifs_sm_req_poolp;
 extern mempool_t *cifs_req_poolp;
@@ -1022,3 +1023,82 @@ int copy_path_name(char *dst, const char *src)
 	name_len++;
 	return name_len;
 }
+
+struct super_cb_data {
+	struct TCP_Server_Info *server;
+	struct super_block *sb;
+};
+
+static void super_cb(struct super_block *sb, void *arg)
+{
+	struct super_cb_data *d = arg;
+	struct cifs_sb_info *cifs_sb;
+	struct cifs_tcon *tcon;
+
+	if (d->sb)
+		return;
+
+	cifs_sb = CIFS_SB(sb);
+	tcon = cifs_sb_master_tcon(cifs_sb);
+	if (tcon->ses->server == d->server)
+		d->sb = sb;
+}
+
+struct super_block *cifs_get_tcp_super(struct TCP_Server_Info *server)
+{
+	struct super_cb_data d = {
+		.server = server,
+		.sb = NULL,
+	};
+
+	iterate_supers_type(&cifs_fs_type, super_cb, &d);
+
+	if (unlikely(!d.sb))
+		return ERR_PTR(-ENOENT);
+	/*
+	 * Grab an active reference in order to prevent automounts (DFS links)
+	 * of expiring and then freeing up our cifs superblock pointer while
+	 * we're doing failover.
+	 */
+	cifs_sb_active(d.sb);
+	return d.sb;
+}
+
+void cifs_put_tcp_super(struct super_block *sb)
+{
+	if (!IS_ERR_OR_NULL(sb))
+		cifs_sb_deactive(sb);
+}
+
+int update_super_prepath(struct cifs_tcon *tcon, const char *prefix,
+			 size_t prefix_len)
+{
+	struct super_block *sb;
+	struct cifs_sb_info *cifs_sb;
+	int rc = 0;
+
+	sb = cifs_get_tcp_super(tcon->ses->server);
+	if (IS_ERR(sb))
+		return PTR_ERR(sb);
+
+	cifs_sb = CIFS_SB(sb);
+
+	kfree(cifs_sb->prepath);
+
+	if (*prefix && prefix_len) {
+		cifs_sb->prepath = kstrndup(prefix, prefix_len, GFP_ATOMIC);
+		if (!cifs_sb->prepath) {
+			rc = -ENOMEM;
+			goto out;
+		}
+
+		convert_delimiter(cifs_sb->prepath, CIFS_DIR_SEP(cifs_sb));
+	} else
+		cifs_sb->prepath = NULL;
+
+	cifs_sb->mnt_cifs_flags |= CIFS_MOUNT_USE_PREFIX_PATH;
+
+out:
+	cifs_put_tcp_super(sb);
+	return rc;
+}

fs/cifs/smb2pdu.c

@@ -193,9 +193,18 @@ static int __smb2_reconnect(const struct nls_table *nlsc,
 
 	for (it = dfs_cache_get_tgt_iterator(&tl); it;
 	     it = dfs_cache_get_next_tgt(&tl, it)) {
-		const char *tgt = dfs_cache_get_tgt_name(it);
+		const char *share, *prefix;
+		size_t share_len, prefix_len;
 
-		extract_unc_hostname(tgt, &dfs_host, &dfs_host_len);
+		rc = dfs_cache_get_tgt_share(it, &share, &share_len, &prefix,
+					     &prefix_len);
+		if (rc) {
+			cifs_dbg(VFS, "%s: failed to parse target share %d\n",
+				 __func__, rc);
+			continue;
+		}
+
+		extract_unc_hostname(share, &dfs_host, &dfs_host_len);
 
 		if (dfs_host_len != tcp_host_len
 		    || strncasecmp(dfs_host, tcp_host, dfs_host_len) != 0) {
@@ -206,11 +215,13 @@ static int __smb2_reconnect(const struct nls_table *nlsc,
 			continue;
 		}
 
-		scnprintf(tree, MAX_TREE_SIZE, "\\%s", tgt);
+		scnprintf(tree, MAX_TREE_SIZE, "\\%.*s", (int)share_len, share);
 
 		rc = SMB2_tcon(0, tcon->ses, tree, tcon, nlsc);
-		if (!rc)
+		if (!rc) {
+			rc = update_super_prepath(tcon, prefix, prefix_len);
 			break;
+		}
 		if (rc == -EREMOTE)
 			break;
 	}