cifs: protect access of TCP_Server_Info::{origin,leaf}_fullpath

Protect access of TCP_Server_Info::{origin,leaf}_fullpath when
matching DFS connections, and get rid of
TCP_Server_Info::current_fullpath while we're at it.

Cc: [e-mail] # v6.2+
Signed-off-by: Paulo Alcantara (SUSE) <[e-mail]>
Signed-off-by: Steve French <[e-mail]>

fs/cifs/cifsglob.h

···
 #endif
 	struct mutex refpath_lock; /* protects leaf_fullpath */
 	/*
-	 * Canonical DFS full paths that were used to chase referrals in mount and reconnect.
+	 * origin_fullpath: Canonical copy of smb3_fs_context::source.
+	 *                  It is used for matching existing DFS tcons.
 	 *
-	 * origin_fullpath: first or original referral path
-	 * leaf_fullpath: last referral path (might be changed due to nested links in reconnect)
+	 * leaf_fullpath: Canonical DFS referral path related to this
+	 *                connection.
+	 *                It is used in DFS cache refresher, reconnect and may
+	 *                change due to nested DFS links.
 	 *
-	 * current_fullpath: pointer to either origin_fullpath or leaf_fullpath
-	 * NOTE: cannot be accessed outside cifs_reconnect() and smb2_reconnect()
+	 * Both protected by @refpath_lock and @srv_lock.  The @refpath_lock is
+	 * mosly used for not requiring a copy of @leaf_fullpath when getting
+	 * cached or new DFS referrals (which might also sleep during I/O).
+	 * While @srv_lock is held for making string and NULL comparions against
+	 * both fields as in mount(2) and cache refresh.
 	 *
-	 * format: \\HOST\SHARE\[OPTIONAL PATH]
+	 * format: \\HOST\SHARE[\OPTIONAL PATH]
 	 */
-	char *origin_fullpath, *leaf_fullpath, *current_fullpath;
+	char *origin_fullpath, *leaf_fullpath;
 };
 
 static inline bool is_smb1(struct TCP_Server_Info *server)

fs/cifs/connect.c

···
 static int reconnect_dfs_server(struct TCP_Server_Info *server)
 {
 	int rc = 0;
-	const char *refpath = server->current_fullpath + 1;
 	struct dfs_cache_tgt_list tl = DFS_CACHE_TGT_LIST_INIT(tl);
 	struct dfs_cache_tgt_iterator *target_hint = NULL;
 	int num_targets = 0;
···
 	 * through /proc/fs/cifs/dfscache or the target list is empty due to server settings after
 	 * refreshing the referral, so, in this case, default it to 1.
 	 */
-	if (!dfs_cache_noreq_find(refpath, NULL, &tl))
+	mutex_lock(&server->refpath_lock);
+	if (!dfs_cache_noreq_find(server->leaf_fullpath + 1, NULL, &tl))
 		num_targets = dfs_cache_get_nr_tgts(&tl);
+	mutex_unlock(&server->refpath_lock);
 	if (!num_targets)
 		num_targets = 1;
 
···
 		mod_delayed_work(cifsiod_wq, &server->reconnect, 0);
 	} while (server->tcpStatus == CifsNeedReconnect);
 
-	dfs_cache_noreq_update_tgthint(refpath, target_hint);
+	mutex_lock(&server->refpath_lock);
+	dfs_cache_noreq_update_tgthint(server->leaf_fullpath + 1, target_hint);
+	mutex_unlock(&server->refpath_lock);
 	dfs_cache_free_tgts(&tl);
 
 	/* Need to set up echo worker again once connection has been established */
···
 			rc = -ENOMEM;
 			goto out_err;
 		}
-		tcp_ses->current_fullpath = tcp_ses->leaf_fullpath;
 	}
 
 	if (ctx->nosharesock)

fs/cifs/dfs.c

···
 		tcon = mnt_ctx->tcon;
 
 		mutex_lock(&server->refpath_lock);
+		spin_lock(&server->srv_lock);
 		if (!server->origin_fullpath) {
 			server->origin_fullpath = origin_fullpath;
-			server->current_fullpath = server->leaf_fullpath;
 			origin_fullpath = NULL;
 		}
+		spin_unlock(&server->srv_lock);
 		mutex_unlock(&server->refpath_lock);
 
 		if (list_empty(&tcon->dfs_ses_list)) {
···
 		rc = PTR_ERR(npath);
 	} else {
 		mutex_lock(&server->refpath_lock);
+		spin_lock(&server->srv_lock);
 		kfree(server->leaf_fullpath);
 		server->leaf_fullpath = npath;
+		spin_unlock(&server->srv_lock);
 		mutex_unlock(&server->refpath_lock);
-		server->current_fullpath = server->leaf_fullpath;
 	}
 	return rc;
 }
···
 		share = prefix = NULL;
 
 		/* Check if share matches with tcp ses */
-		rc = dfs_cache_get_tgt_share(server->current_fullpath + 1, tit, &share, &prefix);
+		rc = dfs_cache_get_tgt_share(server->leaf_fullpath + 1, tit, &share, &prefix);
 		if (rc) {
 			cifs_dbg(VFS, "%s: failed to parse target share: %d\n", __func__, rc);
 			break;
···
 			continue;
 		}
 
-		dfs_cache_noreq_update_tgthint(server->current_fullpath + 1, tit);
+		dfs_cache_noreq_update_tgthint(server->leaf_fullpath + 1, tit);
 		tree_connect_ipc(xid, tree, cifs_sb, tcon);
 
 		scnprintf(tree, MAX_TREE_SIZE, "\\%s", share);
···
 	cifs_sb = CIFS_SB(sb);
 
 	/* If it is not dfs or there was no cached dfs referral, then reconnect to same share */
-	if (!server->current_fullpath ||
-	    dfs_cache_noreq_find(server->current_fullpath + 1, &ref, &tl)) {
+	if (!server->leaf_fullpath ||
+	    dfs_cache_noreq_find(server->leaf_fullpath + 1, &ref, &tl)) {
 		rc = ops->tree_connect(xid, tcon->ses, tcon->tree_name, tcon, cifs_sb->local_nls);
 		goto out;
 	}

fs/cifs/dfs.h

···
 	size_t len;
 	char *s;
 
-	if (unlikely(!server->origin_fullpath))
+	spin_lock(&server->srv_lock);
+	if (unlikely(!server->origin_fullpath)) {
+		spin_unlock(&server->srv_lock);
 		return ERR_PTR(-EREMOTE);
+	}
+	spin_unlock(&server->srv_lock);
 
 	s = dentry_path_raw(dentry, page, PATH_MAX);
 	if (IS_ERR(s))
···
 	if (!s[1])
 		s++;
 
+	spin_lock(&server->srv_lock);
 	len = strlen(server->origin_fullpath);
-	if (s < (char *)page + len)
+	if (s < (char *)page + len) {
+		spin_unlock(&server->srv_lock);
 		return ERR_PTR(-ENAMETOOLONG);
+	}
 
 	s -= len;
 	memcpy(s, server->origin_fullpath, len);
+	spin_unlock(&server->srv_lock);
 	convert_delimiter(s, '/');
+
 	return s;
 }
 

fs/cifs/dfs_cache.c

···
 
 	spin_lock(&cifs_tcp_ses_lock);
 	list_for_each_entry(server, &cifs_tcp_ses_list, tcp_ses_list) {
-		if (!server->leaf_fullpath)
+		spin_lock(&server->srv_lock);
+		if (!server->leaf_fullpath) {
+			spin_unlock(&server->srv_lock);
 			continue;
+		}
+		spin_unlock(&server->srv_lock);
 
 		list_for_each_entry(ses, &server->smb_ses_list, smb_ses_list) {
 			if (ses->tcon_ipc) {