ksmbd: fix race condition between tree conn lookup and disconnect

if thread A in smb2_write is using work-tcon, other thread B use
smb2_tree_disconnect free the tcon, then thread A will use free'd tcon.

                            Time
                             +
 Thread A                    | Thread A
 smb2_write                  | smb2_tree_disconnect
                             |
                             |
                             |   kfree(tree_conn)
                             |
  // UAF!                    |
  work->tcon->share_conf     |
                             +

This patch add state, reference count and lock for tree conn to fix race
condition issue.

Reported-by: luosili <rootlab@huawei.com>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>

1 files changed, 39 insertions, 3 deletions

diff --git a/fs/smb/server/mgmt/tree_connect.c b/fs/smb/server/mgmt/tree_connect.c
index 408cddf2f094..d2c81a8a11dd 100644
--- a/fs/smb/server/mgmt/tree_connect.c
+++ b/fs/smb/server/mgmt/tree_connect.c
@@ -73,7 +73,10 @@ ksmbd_tree_conn_connect(struct ksmbd_conn *conn, struct ksmbd_session *sess,
 
 	tree_conn->user = sess->user;
 	tree_conn->share_conf = sc;
+	tree_conn->t_state = TREE_NEW;
 	status.tree_conn = tree_conn;
+	atomic_set(&tree_conn->refcount, 1);
+	init_waitqueue_head(&tree_conn->refcount_q);
 
 	ret = xa_err(xa_store(&sess->tree_conns, tree_conn->id, tree_conn,
 			      GFP_KERNEL));
@@ -93,14 +96,33 @@ out_error:
 	return status;
 }
 
+void ksmbd_tree_connect_put(struct ksmbd_tree_connect *tcon)
+{
+	/*
+	 * Checking waitqueue to releasing tree connect on
+	 * tree disconnect. waitqueue_active is safe because it
+	 * uses atomic operation for condition.
+	 */
+	if (!atomic_dec_return(&tcon->refcount) &&
+	    waitqueue_active(&tcon->refcount_q))
+		wake_up(&tcon->refcount_q);
+}
+
 int ksmbd_tree_conn_disconnect(struct ksmbd_session *sess,
 			       struct ksmbd_tree_connect *tree_conn)
 {
 	int ret;
 
+	write_lock(&sess->tree_conns_lock);
+	xa_erase(&sess->tree_conns, tree_conn->id);
+	write_unlock(&sess->tree_conns_lock);
+
+	if (!atomic_dec_and_test(&tree_conn->refcount))
+		wait_event(tree_conn->refcount_q,
+			   atomic_read(&tree_conn->refcount) == 0);
+
 	ret = ksmbd_ipc_tree_disconnect_request(sess->id, tree_conn->id);
 	ksmbd_release_tree_conn_id(sess, tree_conn->id);
-	xa_erase(&sess->tree_conns, tree_conn->id);
 	ksmbd_share_config_put(tree_conn->share_conf);
 	kfree(tree_conn);
 	return ret;
@@ -111,11 +133,15 @@ struct ksmbd_tree_connect *ksmbd_tree_conn_lookup(struct ksmbd_session *sess,
 {
 	struct ksmbd_tree_connect *tcon;
 
+	read_lock(&sess->tree_conns_lock);
 	tcon = xa_load(&sess->tree_conns, id);
 	if (tcon) {
-		if (test_bit(TREE_CONN_EXPIRE, &tcon->status))
+		if (tcon->t_state != TREE_CONNECTED)
+			tcon = NULL;
+		else if (!atomic_inc_not_zero(&tcon->refcount))
 			tcon = NULL;
 	}
+	read_unlock(&sess->tree_conns_lock);
 
 	return tcon;
 }
@@ -129,8 +155,18 @@ int ksmbd_tree_conn_session_logoff(struct ksmbd_session *sess)
 	if (!sess)
 		return -EINVAL;
 
-	xa_for_each(&sess->tree_conns, id, tc)
+	xa_for_each(&sess->tree_conns, id, tc) {
+		write_lock(&sess->tree_conns_lock);
+		if (tc->t_state == TREE_DISCONNECTED) {
+			write_unlock(&sess->tree_conns_lock);
+			ret = -ENOENT;
+			continue;
+		}
+		tc->t_state = TREE_DISCONNECTED;
+		write_unlock(&sess->tree_conns_lock);
+
 		ret |= ksmbd_tree_conn_disconnect(sess, tc);
+	}
 	xa_destroy(&sess->tree_conns);
 	return ret;
 }