linux-kernel - Re: [PATCH net-next 2/2] xfrm: Fix unaligned access in xfrm_notify

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Message-Id: <20151021.061737.817854527348057019.davem@davemloft.net>
Date:	Wed, 21 Oct 2015 06:17:37 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	sowmini.varadhan@...cle.com
Cc:	steffen.klassert@...unet.com, linux-crypto@...r.kernel.org,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	herbert@...dor.apana.org.au, dhowells@...hat.com,
	zohar@...ux.vnet.ibm.com, David.Woodhouse@...el.com
Subject: Re: [PATCH net-next 2/2] xfrm: Fix unaligned access in
 xfrm_notify_sa() for DELSA

From: Sowmini Varadhan <sowmini.varadhan@...cle.com>
Date: Wed, 21 Oct 2015 06:54:42 -0400

> On (10/21/15 08:57), Steffen Klassert wrote:
>> > --- a/net/xfrm/xfrm_user.c
>> > +++ b/net/xfrm/xfrm_user.c
>> > @@ -2659,7 +2659,7 @@ static int xfrm_notify_sa(struct xfrm_state *x, const struct km_event *c)
>> >  		if (attr == NULL)
>> >  			goto out_free_skb;
>> >  
>> > -		p = nla_data(attr);
>> > +		p = PTR_ALIGN(nla_data(attr), __alignof__(*p));
>> 
>> Hm, this breaks userspace notifications on 64-bit systems.
>> Userspace expects this to be aligned to 4, with your patch
>> it is aligned to 8 on 64-bit.
>> 
>> Without your patch I get the correct notification when deleting a SA:
>> 
> 
> But __alignof__(*p) is 8 on sparc, and without the patch I get
> all types of unaligned access. So what do you suggest as the fix?

The accesses have to be done using something like get_unaligned() and
put_unaligned().

Sorry, but the protocol is set in stone and this is unfortunately how
it is.
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