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Guillaume Nault f026bc29a8 l2tp: pass tunnel pointer to ->session_create()
Using l2tp_tunnel_find() in pppol2tp_session_create() and
l2tp_eth_create() is racy, because no reference is held on the
returned session. These functions are only used to implement the
->session_create callback which is run by l2tp_nl_cmd_session_create().
Therefore searching for the parent tunnel isn't necessary because
l2tp_nl_cmd_session_create() already has a pointer to it and holds a
reference.

This patch modifies ->session_create()'s prototype to directly pass the
the parent tunnel as parameter, thus avoiding searching for it in
pppol2tp_session_create() and l2tp_eth_create().

Since we have to touch the ->session_create() call in
l2tp_nl_cmd_session_create(), let's also remove the useless conditional:
we know that ->session_create isn't NULL at this point because it's
already been checked earlier in this same function.

Finally, one might be tempted to think that the removed
l2tp_tunnel_find() calls were harmless because they would return the
same tunnel as the one held by l2tp_nl_cmd_session_create() anyway.
But that tunnel might be removed and a new one created with same tunnel
Id before the l2tp_tunnel_find() call. In this case l2tp_tunnel_find()
would return the new tunnel which wouldn't be protected by the
reference held by l2tp_nl_cmd_session_create().

Fixes: 309795f4be ("l2tp: Add netlink control API for L2TP")
Fixes: d9e31d17ce ("l2tp: Add L2TP ethernet pseudowire support")
Signed-off-by: Guillaume Nault <g.nault@alphalink.fr>
Signed-off-by: David S. Miller <davem@davemloft.net>
History 2017-09-03 11:04:21 -07:00
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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.