linux-kernel - Re: [2.6 patch] acpi/ec.c: fix use-after-free

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Date:	Wed, 24 Oct 2007 21:30:19 +0400
From:	Alexey Starikovskiy <astarikovskiy@...e.de>
To:	Adrian Bunk <bunk@...nel.org>
CC:	Alexey Starikovskiy <aystarik@...il.com>,
	Len Brown <len.brown@...el.com>, linux-acpi@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [2.6 patch] acpi/ec.c: fix use-after-free

Adrian Bunk wrote:
> On Wed, Oct 24, 2007 at 09:15:18PM +0400, Alexey Starikovskiy wrote:
>> Adrian,
>>
>> commit 30c08574da0ead1a47797ce028218ce5b2de61c7 can not introduce use-after-free.
>>
>> Please check...
> 
> 
> Commit 30c08574da0ead1a47797ce028218ce5b2de61c7 did:
> 
> <--  snip  -->
> 
>  	list_for_each_entry(handler, &ec->list, node) {
>                 if (query_bit == handler->query_bit) {
>                         list_del(&handler->node);
>                         kfree(handler);
> -                       break;
>                 }
> 	}
> 
> <--  snip  -->
> 
> 
> If you look at the definition of list_for_each_entry() in 
> include/linux/list.h:
> 
> <--  snip  -->
> 
> #define list_for_each_entry(pos, head, member)                          \
>         for (pos = list_entry((head)->next, typeof(*pos), member);      \
>              prefetch(pos->member.next), &pos->member != (head);        \
>              pos = list_entry(pos->member.next, typeof(*pos), member))
>                               ^^^^^^^^^^^^^^^^
> 
> <--  snip  -->
> 
> 
> Without the "break", "handler" is being dereferenced after it was freed.
Yes, found it minute before :( 
Acked, thanks.
> 
> 
>> Regards,
>> Alex.
>> Adrian Bunk wrote:
>>> This patch fixes a use-after-free introduced by
>>> commit 30c08574da0ead1a47797ce028218ce5b2de61c7.
>>>
>>> Spotted by the Coverity checker.
>>>
>>> Signed-off-by: Adrian Bunk <bunk@...nel.org>
>>>
>>> ---
>>> --- linux-2.6/drivers/acpi/ec.c.old	2007-10-23 19:39:47.000000000 +0200
>>> +++ linux-2.6/drivers/acpi/ec.c	2007-10-23 19:34:55.000000000 +0200
>>> @@ -434,11 +442,11 @@
>>>  EXPORT_SYMBOL_GPL(acpi_ec_add_query_handler);
>>>  
>>>  void acpi_ec_remove_query_handler(struct acpi_ec *ec, u8 query_bit)
>>>  {
>>> -	struct acpi_ec_query_handler *handler;
>>> +	struct acpi_ec_query_handler *handler, *tmp;
>>>  	mutex_lock(&ec->lock);
>>> -	list_for_each_entry(handler, &ec->list, node) {
>>> +	list_for_each_entry_safe(handler, tmp, &ec->list, node) {
>>>  		if (query_bit == handler->query_bit) {
>>>  			list_del(&handler->node);
>>>  			kfree(handler);
>>>  		}
>>>
> 
> 
> cu
> Adrian
> 

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