linux-kernel - Re: [PATCH v3 0/3] Send audit/procinfo/cgroup data in socket-level control message

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Date:	Wed, 04 Sep 2013 17:40:19 +0200
From:	Jan Kaluža <jkaluza@...hat.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	Richard Guy Briggs <rgb@...hat.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>, davem@...emloft.net,
	LKML <linux-kernel@...r.kernel.org>, netdev@...r.kernel.org,
	eparis@...hat.com, tj@...nel.org, lizefan@...wei.com,
	containers@...ts.linux-foundation.org, cgroups@...r.kernel.org,
	viro@...iv.linux.org.uk
Subject: Re: [PATCH v3 0/3] Send audit/procinfo/cgroup data in socket-level
 control message

On 09/04/2013 05:30 PM, Eric Dumazet wrote:
> On Wed, 2013-09-04 at 11:20 -0400, Richard Guy Briggs wrote:
>> On Wed, Sep 04, 2013 at 10:58:30AM -0400, Richard Guy Briggs wrote:
>>> On Wed, Sep 04, 2013 at 12:42:26AM -0700, Eric W. Biederman wrote:
>>>> Jan Kaluza <jkaluza@...hat.com> writes:
>>>>> this patchset against net-next (applies also to linux-next) adds 3 new types
>>>>> of "Socket"-level control message (SCM_AUDIT, SCM_PROCINFO and SCM_CGROUP).
>>>
>>>> By my count you have overflowed cb in struct sk_buff and are stomping on
>>>> _skb_refdest.
>>>
>>> For patch1/3 I count 56/48, then for patch3 I get 48/48.  Jan, you might
>>> do the conversion to a pointer in patch1/3 to avoid bisect breakage.
>>
>> Wait, that __aligned(8) is for cb[48], not for the contents.
>>
>> For patch1/3 I count 28/48 on 32-bit, 36/48 on 64-bit (or would that be
>> 56 by default on 64-bit arches without aligned specified?), then for
>> patch3 I get 24/48 on 32 and 40/48 on 64 (or again 48/48 by default?).
>
> Do not count, just add this :
>
> diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
> index 86de99a..5b61320 100644
> --- a/net/unix/af_unix.c
> +++ b/net/unix/af_unix.c
> @@ -1329,6 +1329,7 @@ static void unix_detach_fds(struct scm_cookie *scm, struct sk_buff *skb)
>   {
>   	int i;
>
> +	BUILD_BUG_ON(sizeof(struct unix_skb_parms) > sizeof(skb->cb));
>   	scm->fp = UNIXCB(skb).fp;
>   	UNIXCB(skb).fp = NULL;
>

That's already in af_unix.c:

BUILD_BUG_ON(sizeof(struct unix_skb_parms) > FIELD_SIZEOF(struct 
sk_buff, cb));

This test is passing for me even with only patch1/3 applied when 
building 64bit kernel.

Jan Kaluza

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