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cf52572ebb
There are two problems with nft_compat since the netlink config
plane uses a per-netns mutex:
1. Concurrent add/del accesses to the same list
2. accesses to a list element after it has been free'd already.
This patch fixes the first problem.
Freeing occurs from a work queue, after transaction mutexes have been
released, i.e., it still possible for a new transaction (even from
same net ns) to find the to-be-deleted expression in the list.
The ->destroy functions are not allowed to have any such side effects,
i.e. the list_del() in the destroy function is not allowed.
This part of the problem is solved in the next patch.
I tried to make this work by serializing list access via mutex
and by moving list_del() to a deactivate callback, but
Taehee spotted following race on this approach:
NET #0 NET #1
>select_ops()
->init()
->select_ops()
->deactivate()
->destroy()
nft_xt_put()
kfree_rcu(xt, rcu_head);
->init() <-- use-after-free occurred.
Unfortunately, we can't increment reference count in
select_ops(), because we can't undo the refcount increase in
case a different expression fails in the same batch.
(The destroy hook will only be called in case the expression
was initialized successfully).
Fixes:
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
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.