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There are several ways to remove L2TP sessions:
* deleting a session explicitly using the netlink interface (with
L2TP_CMD_SESSION_DELETE),
* deleting the session's parent tunnel (either by closing the
tunnel's file descriptor or using the netlink interface),
* closing the PPPOL2TP file descriptor of a PPP pseudo-wire.
In some cases, when these methods are used concurrently on the same
session, the session can be removed twice, leading to use-after-free
bugs.
This patch adds a 'dead' flag, used by l2tp_session_delete() and
l2tp_tunnel_closeall() to prevent them from stepping on each other's
toes.
The session deletion path used when closing a PPPOL2TP file descriptor
doesn't need to be adapted. It already has to ensure that a session
remains valid for the lifetime of its PPPOL2TP file descriptor.
So it takes an extra reference on the session in the ->session_close()
callback (pppol2tp_session_close()), which is eventually dropped
in the ->sk_destruct() callback of the PPPOL2TP socket
(pppol2tp_session_destruct()).
Still, __l2tp_session_unhash() and l2tp_session_queue_purge() can be
called twice and even concurrently for a given session, but thanks to
proper locking and re-initialisation of list fields, this is not an
issue.
Signed-off-by: Guillaume Nault <g.nault@alphalink.fr>
Signed-off-by: David S. Miller <davem@davemloft.net>
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.