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Tetsuo Handa ba6f0d1832 can: j1939: make j1939_session_activate() fail if device is no longer registered
[ Upstream commit 5d5602236f ]

syzbot is still reporting

  unregister_netdevice: waiting for vcan0 to become free. Usage count = 2

even after commit 93a27b5891 ("can: j1939: add missing calls in
NETDEV_UNREGISTER notification handler") was added. A debug printk() patch
found that j1939_session_activate() can succeed even after
j1939_cancel_active_session() from j1939_netdev_notify(NETDEV_UNREGISTER)
has completed.

Since j1939_cancel_active_session() is processed with the session list lock
held, checking ndev->reg_state in j1939_session_activate() with the session
list lock held can reliably close the race window.

Reported-by: syzbot <syzbot+881d65229ca4f9ae8c84@syzkaller.appspotmail.com>
Closes: https://syzkaller.appspot.com/bug?extid=881d65229ca4f9ae8c84
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Acked-by: Oleksij Rempel <o.rempel@pengutronix.de>
Link: https://patch.msgid.link/b9653191-d479-4c8b-8536-1326d028db5c@I-love.SAKURA.ne.jp
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>
History 2026-01-17 16:31:28 +01:00
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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 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.