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

From: Sowmini Varadhan <redacted>
Date: Wed, 21 Oct 2015 06:54:42 -0400

On (10/21/15 08:57), Steffen Klassert wrote:

quoted

quoted

--- 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.