linux-kernel - Re: [PATCH] cfg80211: reg: Fix use-after-free in call

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Date:   Fri, 22 Feb 2019 14:00:08 +0100
From:   Johannes Berg <johannes@...solutions.net>
To:     Yue Haibing <yuehaibing@...wei.com>, davem@...emloft.net
Cc:     linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        linux-wireless@...r.kernel.org
Subject: Re: [PATCH] cfg80211: reg: Fix use-after-free in call_crda

Hi,

> In function reg_query_database, query_regdb_file call
> request_firmware_nowait to do request_firmware asynchronously,
> which need the caller hold the reference of dev, otherwise it will
> do put_device freeing '&reg_pdev->dev'. After that, call_crda access
> the dev will trigger use-after-free bug.

So ... OK, but how does that then only fix the firmware file loading,
rather than CRDA calling?

> This patch fix this by holding a reference of dev in regulatory_init
> after platform_device_register_simple registered successly, which
> releasing in platform_device_unregister.

This doesn't make sense? You just add a new reference and don't release
it? If there was a bug then just loading & unloading would trigger an
underflow now?

platform_device_register_full() (to which _simple is a wrapper) will
evidently return the pdev with a reference held, because it does
platform_device_put() in the error path?

johannes