From: David Ahern <d...@cumulusnetworks.com>
Date: Tue, 25 Apr 2017 09:17:29 -0700
> 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.
>
> 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>
Applied and queued up for -stable, thanks David!
