Re: [PATCH net-next 2/2] xfrm: Fix unaligned access in xfrm_notify_sa() for DELSA

From: David Miller
Date: Wed Oct 21 2015 - 08:54:25 EST


From: Steffen Klassert <steffen.klassert@xxxxxxxxxxx>
Date: Wed, 21 Oct 2015 08:57:04 +0200

> On Mon, Oct 19, 2015 at 05:23:29PM -0400, Sowmini Varadhan wrote:
>> On sparc, deleting established SAs (e.g., by restarting ipsec
>> at the peer) results in unaligned access messages via
>> xfrm_del_sa -> km_state_notify -> xfrm_send_state_notify().
>> Use an aligned pointer to xfrm_usersa_info for this case.
>>
>> Signed-off-by: Sowmini Varadhan <sowmini.varadhan@xxxxxxxxxx>
>> ---
>> net/xfrm/xfrm_user.c | 2 +-
>> 1 files changed, 1 insertions(+), 1 deletions(-)
>>
>> diff --git a/net/xfrm/xfrm_user.c b/net/xfrm/xfrm_user.c
>> index a8de9e3..158ef4a 100644
>> --- 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.

That's correct, netlink attributes are fundamentally only 4 byte
aligned and this cannot be changed. nla_data() is exactly
where the attribute must be placed, aligned or not.

The only workaround is, when designing netlink attributes. Various
netlink libraries have workarounds for accessing, for example, 64-bit
stats which are going to be unaligned in netlink messages.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/