On Mon, 2017-04-24 at 08:09 -0700, David Ahern wrote:
> Taking down the loopback device wreaks havoc on IPv6 routing. By
> extension, taking down a VRF device wreaks havoc on its table.
>
> Dmitry and Andrey both reported heap out-of-bounds reports in the IPv6
> FIB code while running syzkaller fuzzer. The root cause is a dead dst
> that is on the garbage list gets reinserted into the IPv6 FIB. While on
> the gc (or perhaps when it gets added to the gc list) the dst->next is
> set to an IPv4 dst. A subsequent walk of the ipv6 tables causes the
> out-of-bounds access.
>
> Andrey's reproducer was the key to getting to the bottom of this.
>
> With IPv6, host routes for an address have the dst->dev set to the
> loopback device. When the 'lo' device is taken down, rt6_ifdown initiates
> a walk of the fib evicting routes with the 'lo' device which means all
> host routes are removed. That process moves the dst which is attached to
> an inet6_ifaddr to the gc list and marks it as dead.
>
> The recent change to keep global IPv6 addresses added a new function,
> fixup_permanent_addr, that is called on admin up. That function restarts
> dad for an inet6_ifaddr and when it completes the host route attached
> to it is inserted into the fib. Since the route was marked dead and
> moved to the gc list, re-inserting the route causes the reported
> out-of-bounds accesses. If the device with the address is taken down
> or the address is removed, the WARN_ON in fib6_del is triggered.
>
> All of those faults are fixed by regenerating the host route if the
> existing one has been moved to the gc list, something that can be
> determined by checking if the rt6i_ref counter is 0.
Very nice changelog !
>
> Fixes: f1705ec197e7 ("net: ipv6: Make address flushing on ifdown optional")
> Reported-by: Dmitry Vyukov <dvyu...@google.com>
> Reported-by: Andrey Konovalov <andreyk...@google.com>
> Signed-off-by: David Ahern <d...@cumulusnetworks.com>
> ---
> v3
> - removed 'if (prev)' and just call ip6_rt_put; added comment about spinlock
>
> v2
> - change ifp->rt under spinlock vs cmpxchg
> - add comment about rt6i_ref == 0
>
> net/ipv6/addrconf.c | 15 +++++++++++++--
> 1 file changed, 13 insertions(+), 2 deletions(-)
>
> diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
> index 80ce478c4851..93f81d9cd85f 100644
> --- a/net/ipv6/addrconf.c
> +++ b/net/ipv6/addrconf.c
> @@ -3271,14 +3271,25 @@ static void addrconf_gre_config(struct net_device
> *dev)
> static int fixup_permanent_addr(struct inet6_dev *idev,
> struct inet6_ifaddr *ifp)
> {
> - if (!ifp->rt) {
> - struct rt6_info *rt;
> + /* rt6i_ref == 0 means the host route was removed from the
> + * FIB, for example, if 'lo' device is taken down. In that
> + * case regenerate the host route.
> + */
> + if (!ifp->rt || !atomic_read(&ifp->rt->rt6i_ref)) {
> + struct rt6_info *rt, *prev;
>
> rt = addrconf_dst_alloc(idev, &ifp->addr, false);
> if (unlikely(IS_ERR(rt)))
> return PTR_ERR(rt);
>
> + prev = ifp->rt;
I would feel more comfortable if this was moved after the spin_lock() ?
> +
> + /* ifp->rt can be accessed outside of rtnl */
> + spin_lock(&ifp->lock);
> ifp->rt = rt;
> + spin_unlock(&ifp->lock);
> +
> + ip6_rt_put(prev);
> }
>
> if (!(ifp->flags & IFA_F_NOPREFIXROUTE)) {
Thanks !
