[PATCH v2 2/4] smb/server: fix session leak in ksmbd_session_register()

See the procedure below:

  smb2_sess_setup
    ksmbd_smb2_session_create
      __session_create
        atomic_set(&sess->refcnt, 2)
        hash_add(sessions_table, &sess->hlist, sess->id)
    ksmbd_session_register
      xa_store(&conn->sessions, sess->id, sess) // fail
    ksmbd_user_session_put
      atomic_dec(&sess->refcnt) // refcnt is 1, session is not freed

Remove the session from sessions_table and drop its table reference if
xa_store() fails.

Fixes: f5c779b7ddbd ("ksmbd: fix racy issue from session setup and logoff")
Signed-off-by: Ze Tan <[email protected]>
Reviewed-by: ChenXiaoSong <[email protected]>
---
 fs/smb/server/mgmt/user_session.c | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/fs/smb/server/mgmt/user_session.c b/fs/smb/server/mgmt/user_session.c
index a72dc0211d0d..0fc26012dbbb 100644
--- a/fs/smb/server/mgmt/user_session.c
+++ b/fs/smb/server/mgmt/user_session.c
@@ -451,10 +451,21 @@ static void ksmbd_expire_session(struct ksmbd_conn *conn)
 int ksmbd_session_register(struct ksmbd_conn *conn,
 			   struct ksmbd_session *sess)
 {
+	int ret;
+
 	sess->dialect = conn->dialect;
 	memcpy(sess->ClientGUID, conn->ClientGUID, SMB2_CLIENT_GUID_SIZE);
 	ksmbd_expire_session(conn);
-	return xa_err(xa_store(&conn->sessions, sess->id, sess, KSMBD_DEFAULT_GFP));
+	ret = xa_err(xa_store(&conn->sessions, sess->id, sess,
+			      KSMBD_DEFAULT_GFP));
+	if (ret) {
+		down_write(&sessions_table_lock);
+		hash_del(&sess->hlist);
+		up_write(&sessions_table_lock);
+		ksmbd_user_session_put(sess);
+	}
+
+	return ret;
 }
 
 static int ksmbd_chann_del(struct ksmbd_conn *conn, struct ksmbd_session *sess)
-- 
2.55.0