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l2tp_tunnel_destruct() sets tunnel->sock to NULL, then removes the tunnel from the pernet list and finally closes all its sessions. Therefore, it's possible to add a session to a tunnel that is still reachable, but for which tunnel->sock has already been reset. This can make l2tp_session_create() dereference a NULL pointer when calling sock_hold(tunnel->sock). This patch adds the .acpt_newsess field to struct l2tp_tunnel, which is used by l2tp_tunnel_closeall() to prevent addition of new sessions to tunnels. Resetting tunnel->sock is done after l2tp_tunnel_closeall() returned, so that l2tp_session_add_to_tunnel() can safely take a reference on it when .acpt_newsess is true. The .acpt_newsess field is modified in l2tp_tunnel_closeall(), rather than in l2tp_tunnel_destruct(), so that it benefits all tunnel removal mechanisms. E.g. on UDP tunnels, a session could be added to a tunnel after l2tp_udp_encap_destroy() proceeded. This would prevent the tunnel from being removed because of the references held by this new session on the tunnel and its socket. Even though the session could be removed manually later on, this defeats the purpose of commit |
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| README | ||
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.