linux-kernel - [RFC char-misc-next 0/2] Add private pointer to struct cdev

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Message-Id: <cover.1641185192.git.dxu@dxuuu.xyz>
Date:   Sun,  2 Jan 2022 21:01:38 -0800
From:   Daniel Xu <dxu@...uu.xyz>
To:     arnd@...db.de, gregkh@...uxfoundation.org, giometti@...eenne.com,
        linux-kernel@...r.kernel.org
Cc:     Daniel Xu <dxu@...uu.xyz>, thesven73@...il.com, ojeda@...nel.org
Subject: [RFC char-misc-next 0/2] Add private pointer to struct cdev

The details are explained more thoroughly in the actual commits, but the
basic idea behind this RFC patchset is that:

* Using cdev_init() on an embedded struct cdev can lead to subtle
  use-after-free issues
* Switching to cdev_alloc() and storing a pointer fixes the lifetime
  issues but also breaks container_of()
* Deal with container_of() breakage by adding a void *private field

I've "fixed" (I'm aware module unloading is best-effort and may not
constitute a "real" bug) the issue in a random driver I found that
exhibits the issue. The other drivers I've seen with the issue are hard
for me to load/unload, so just one for now.

If this patchset is deemed acceptable, I'd be happy to convert other
broken drivers I find, but with the understanding that the best I can do
for testing is compiling them.

Daniel Xu (2):
  cdev: Add private pointer to struct cdev
  pps: Fix use-after-free cdev bug on module unload

 drivers/pps/pps.c          | 20 +++++++++++---------
 include/linux/cdev.h       |  1 +
 include/linux/pps_kernel.h |  2 +-
 3 files changed, 13 insertions(+), 10 deletions(-)

-- 
2.34.1