[PATCH IPv6] Fix race condition in ipv6_add_addr

[Olaf Kirch <okir@suse.de>]

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Here's a patch originally from Keir Fraser, which we included in SLES10,
but which we forgot to submit upstream so far.

During stress testing, machines were frequently crashing in
__ipv6_ifa_notify on dst_hold(&ifp->rt.u_dst), with ifp->rt being a
NULL pointer.

The attached patch fixes the problem.

Thanks,
Olaf
-- 
Olaf Kirch   |  --- o --- Nous sommes du soleil we love when we play
okir@suse.de |    / | \   sol.dhoop.naytheet.ah kin.ir.samse.qurax

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From: Keir Fraser <keir.fraser@cl.cam.ac.uk>
Subject: ipv6_add_addr should install dstentry earlier

ipv6_add_addr allocates a struct inet6_ifaddr and a dstentry, but it
doesn't install the dstentry in ifa->rt until after it releases the
addrconf_hash_lock. This means other CPUs will be able to see the new
address while it hasn't been initialized completely yet.

One possible fix would be to grab the ifp->lock spinlock when
creating the address struct; a simpler fix is to just move the
assignment.

Acked-by: jbeulich@novell.com
Acked-by: okir@suse.de

--- linux-2.6.16.13-old/net/ipv6/addrconf.c	2006-05-02 22:38:44.000000000 +0100
+++ linux-2.6.16.13-new/net/ipv6/addrconf.c	2006-06-18 10:16:50.000000000 +0100
@@ -549,6 +549,8 @@
 	ifa->flags = flags | IFA_F_TENTATIVE;
 	ifa->cstamp = ifa->tstamp = jiffies;
 
+	ifa->rt = rt;
+
 	ifa->idev = idev;
 	in6_dev_hold(idev);
 	/* For caller */
@@ -575,8 +577,6 @@
 	}
 #endif
 
-	ifa->rt = rt;
-
 	in6_ifa_hold(ifa);
 	write_unlock(&idev->lock);
 out2: