[RFC v1 0/3] Address potential user-after-free on module unload

[Sven Van Asbroeck]

I think there _might_ be potential use-after-free issues on module unload.

They are hard to trigger, but I think I've seen them bring the whole
kernel down when they do occur. Can be triggered by doing an insmod of
a vulnerable module, rapidly followed by an rmmod.

Caused by drivers which schedule work / delayed_work, but do not clean it up
properly on module unload. Which means the work function could run _after_
the module has unloaded.

A quick grep through the kernel sources brings up many instances.
I leave it to people more knowledgeable than me to determine if this problem
is likely to happen, and/or if it can be exploited to become a security risk.

Perhaps developers can be 'nudged' into doing the right thing by using
resource-managed versions of INIT_WORK() / INIT_DELAYED_WORK(), which may
address the issue quite elegantly.

Attached is a proposal patch, followed by sample fixes for two vulnerable
modules. As far as I can tell, many more modules are vulnerable.

Sven Van Asbroeck (3):
  workqueue: Add resource-managed version of INIT_[DELAYED_]WORK()
  max17042_battery: fix potential user-after-free on module unload
  cap11xx: fix potential user-after-free on module unload

 drivers/input/keyboard/cap11xx.c        |  6 ++-
 drivers/power/supply/max17042_battery.c |  5 ++-
 include/linux/workqueue.h               |  7 ++++
 kernel/workqueue.c                      | 54 +++++++++++++++++++++++++
 4 files changed, 70 insertions(+), 2 deletions(-)

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2.17.1