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James Chapman a487cc8986 net/l2tp: fix warning in l2tp_exit_net found by syzbot 
[ Upstream commit 5d066766c5 ]

In l2tp's net exit handler, we check that an IDR is empty before
destroying it:

	WARN_ON_ONCE(!idr_is_empty(&pn->l2tp_tunnel_idr));
	idr_destroy(&pn->l2tp_tunnel_idr);

By forcing memory allocation failures in idr_alloc_32, syzbot is able
to provoke a condition where idr_is_empty returns false despite there
being no items in the IDR. This turns out to be because the radix tree
of the IDR contains only internal radix-tree nodes and it is this that
causes idr_is_empty to return false. The internal nodes are cleaned by
idr_destroy.

Use idr_for_each to check that the IDR is empty instead of
idr_is_empty to avoid the problem.

Reported-by: syzbot+332fe1e67018625f63c9@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=332fe1e67018625f63c9
Fixes: 73d33bd063 ("l2tp: avoid using drain_workqueue in l2tp_pre_exit_net")
Signed-off-by: James Chapman <jchapman@katalix.com>
Link: https://patch.msgid.link/20241118140411.1582555-1-jchapman@katalix.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
History 2024-12-05 14:02:31 +01:00
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README

README 

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 reStructuredText 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.