linux-kernel - Re: [PATCH] HID: hid-input: Fix accessing freed memory during driver unbind

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Date:	Thu, 30 Jul 2015 08:42:12 +0900
From:	Krzysztof Kozlowski <k.kozlowski@...sung.com>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:	Jiri Kosina <jkosina@...e.com>,
	Krzysztof Kozlowski <k.kozlowski@...sung.com>,
	linux-input@...r.kernel.org, linux-kernel@...r.kernel.org,
	sre@...nel.org, linux-pm@...r.kernel.org,
	"H.J. Lu" <hjl.tools@...il.com>, stable@...r.kernel.org
Subject: Re: [PATCH] HID: hid-input: Fix accessing freed memory during driver unbind

2015-07-30 2:46 GMT+09:00 Dmitry Torokhov <dmitry.torokhov@...il.com>:
> On Wed, Jul 29, 2015 at 03:07:04PM +0200, Jiri Kosina wrote:
>> On Tue, 28 Jul 2015, Krzysztof Kozlowski wrote:
>>
>> > During unbinding the driver was dereferencing a pointer to memory
>> > already freed by power_supply_unregister().
>> >
>> > Driver was freeing its internal description of battery through pointers
>> > stored in power_supply structure. However, because the core owns the
>> > power supply instance, after calling power_supply_unregister() the
>> > driver cannot access these members.
>> >
>> > Fix this by using resource-managed allocations so internal data will be
>> > freed by pointers stored in resource-managed core.
>> >
>> > Signed-off-by: Krzysztof Kozlowski <k.kozlowski@...sung.com>
>> > Reported-by: H.J. Lu <hjl.tools@...il.com>
>> > Fixes: 297d716f6260 ("power_supply: Change ownership from driver to core")
>> > Cc: <stable@...r.kernel.org>
>>
>> Applied to for-4.2/upstream-fixes, thanks.
>
> Wait, what guarantees do we have that this is only called in probe()
> paths? Don't we allow hid_hw_start() be deferred to open() calls?

Indeed, this may be called in other contexts. But this should not
introduce errors except not reclaimable memory (till remove()
happens).

> In general we need to be careful with devm* conversions in core code.
>

Another and less intrusive fix would be:

    char *name = dev->battery->desc->name;
    struct power_supply_desc *psy_desc = dev->battery->desc;
    power_supply_unregister(dev->battery);
    kfree(name);
    kfree(psy_desc);

How about this?

Best regards,
Krzysztof
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