linux-kernel - Re: [PATCH 1/2] devcoredump: Remove devcoredump device if failing device is gone

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Date: Tue, 30 Jan 2024 16:51:57 +0100
From: Johannes Berg <johannes@...solutions.net>
To: Rodrigo Vivi <rodrigo.vivi@...el.com>
Cc: linux-kernel@...r.kernel.org, Jose Souza <jose.souza@...el.com>, Maarten
 Lankhorst <maarten.lankhorst@...ux.intel.com>, Greg Kroah-Hartman
 <gregkh@...uxfoundation.org>,  "Rafael J . Wysocki" <rafael@...nel.org>
Subject: Re: [PATCH 1/2] devcoredump: Remove devcoredump device if failing
 device is gone

On Tue, 2024-01-30 at 10:49 -0500, Rodrigo Vivi wrote:
> 
> I will make changes to our driver to make the 'data' a standalone memory
> that devcoredump will free. this ensures no uaf and no null deref.
> data could be read even after unbinding the driver.
> 
> What I meant to userspace 'writing to 'data'' was to ensure that
> on our CI we run something like
> 
> if /sys/.../device/devcd<n> exists, then
> echo 1 > /sys/.../device/devcd<n>/data
> before attempting the rmmod <driver>
> 
> our rmmod cannot get stuck or our CI is blocked, but then ensuring
> the devcd is gone with module_put happening is the only current way
> of not blocking the rmmod.
> 

Ah, you were just concerned about the module removal, sure, that makes
sense.

Though depending on how you make that data pointer: if you just use
*sg() or *v() then you don't have this problem in the first place. OTOH,
it's probably good to have a udev rule to automatically capture the data
in CI anyway (and fail the test if it happened?)

johannes