linux-kernel - Re: net: sctp: possible dereference after freeing

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Message-Id: <DA7AE80C-302D-4B9D-9C0E-BA980E25DFCE@gmail.com>
Date:	Sat, 19 Oct 2013 13:36:35 -0400
From:	Vlad Yasevich <vyasevich@...il.com>
To:	Geyslan Gregório Bem <geyslan@...il.com>
Cc:	Neil Horman <nhorman@...driver.com>,
	"David S. Miller" <davem@...emloft.net>,
	"linux-sctp@...r.kernel.org" <linux-sctp@...r.kernel.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: net: sctp: possible dereference after freeing



On Oct 19, 2013, at 7:49 AM, Geyslan Gregório Bem <geyslan@...il.com> wrote:

> 2013/10/19 Geyslan Gregório Bem <geyslan@...il.com>:
>> Hi maintainers,
>> 
>> I would like to know if these are catches:
>> 
>> /net/sctp/endpointola.c (281)
>> static void sctp_endpoint_destroy(struct sctp_endpoint *ep)
>> {
>>    struct sock *sk;
>> ...
>>    kfree(ep);
>>    SCTP_DBG_OBJCNT_DEC(ep);
>> }
>> 
>> The 'ep' object counter is being decremented?! Is the kfree to be there indeed?
>> Let me know what was intended here.
>> 
>> Same here:
>> /net/sctp/endpointola.c (165)
>> static void sctp_transport_destroy_rcu(struct rcu_head *head)
>> {
>>    struct sctp_transport *transport;
>> ...
>>    kfree(transport);
>>    SCTP_DBG_OBJCNT_DEC(transport);
>> }
>> 
>> Regards,
>> 
>> Geyslan Gregório Bem
>> hackingbits.com
> 
> Oops. I got it. ;)
> 
> extern atomic_t sctp_dbg_objcnt_ep;
> http://lxr.free-electrons.com/source/include/net/sctp/sctp.h#L269
> extern atomic_t sctp_dbg_objcnt_transport;
> http://lxr.free-electrons.com/source/arch/x86/include/asm/atomic.h#L105
> 
> Cheers.

There is no reference here since the macro turns variable name to string using ## name.
So the order doesn't matter really.

-vlad --
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