Date:   Tue, 25 Apr 2017 14:50:40 +0200
From:   Andrey Konovalov <andreyknvl@...gle.com>
To:     David Ahern <dsa@...ulusnetworks.com>
Cc:     netdev <netdev@...r.kernel.org>,
        Dmitry Vyukov <dvyukov@...gle.com>, mmanning@...cade.com,
        Martin KaFai Lau <kafai@...com>
Subject: Re: [PATCH v3 net] net: ipv6: regenerate host route if moved to gc list

On Mon, Apr 24, 2017 at 5:09 PM, David Ahern <dsa@...ulusnetworks.com> 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.

Hi David,

I've been running syzkaller with your patch and got another report
from ip6_pol_route.

It happened only once so far and I couldn't reproduce it.

==================================================================
BUG: KASAN: slab-out-of-bounds in find_rr_leaf net/ipv6/route.c:722
[inline] at addr ffff880033dddaa8
BUG: KASAN: slab-out-of-bounds in rt6_select net/ipv6/route.c:758
[inline] at addr ffff880033dddaa8
BUG: KASAN: slab-out-of-bounds in ip6_pol_route+0x1b1e/0x1ba0
net/ipv6/route.c:1091 at addr ffff880033dddaa8
Read of size 4 by task syz-executor7/9808
CPU: 2 PID: 9808 Comm: syz-executor7 Not tainted 4.11.0-rc8+ #268
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:16 [inline]
 dump_stack+0x192/0x22d lib/dump_stack.c:52
 kasan_object_err+0x1c/0x70 mm/kasan/report.c:164
 print_address_description mm/kasan/report.c:202 [inline]
 kasan_report_error mm/kasan/report.c:291 [inline]
 kasan_report+0x252/0x510 mm/kasan/report.c:347
 __asan_report_load4_noabort+0x14/0x20 mm/kasan/report.c:367
 find_rr_leaf net/ipv6/route.c:722 [inline]
 rt6_select net/ipv6/route.c:758 [inline]
 ip6_pol_route+0x1b1e/0x1ba0 net/ipv6/route.c:1091
 ip6_pol_route_output+0x4c/0x60 net/ipv6/route.c:1212
 fib6_rule_action+0x261/0x8a0 net/ipv6/fib6_rules.c:100
 fib_rules_lookup+0x34b/0xae0 net/core/fib_rules.c:265
 fib6_rule_lookup+0x175/0x360 net/ipv6/fib6_rules.c:44
 ip6_route_output_flags+0x260/0x2f0 net/ipv6/route.c:1240
 ip6_route_output include/net/ip6_route.h:79 [inline]
 ip6_dst_lookup_tail+0xe59/0x1640 net/ipv6/ip6_output.c:959
 ip6_dst_lookup_flow+0xb1/0x260 net/ipv6/ip6_output.c:1082
 ip6_sk_dst_lookup_flow+0x2c6/0x7f0 net/ipv6/ip6_output.c:1113
 udpv6_sendmsg+0x2350/0x3310 net/ipv6/udp.c:1219
 inet_sendmsg+0x164/0x490 net/ipv4/af_inet.c:762
 sock_sendmsg_nosec net/socket.c:633 [inline]
 sock_sendmsg+0xca/0x110 net/socket.c:643
 SYSC_sendto+0x660/0x810 net/socket.c:1696
 SyS_sendto+0x40/0x50 net/socket.c:1664
 entry_SYSCALL_64_fastpath+0x1a/0xa9
RIP: 0033:0x4458d9
RSP: 002b:00007ff3a5343b58 EFLAGS: 00000282 ORIG_RAX: 000000000000002c
RAX: ffffffffffffffda RBX: 0000000000708000 RCX: 00000000004458d9
RDX: 0000000000000fa8 RSI: 0000000020000000 RDI: 0000000000000005
RBP: 0000000000004300 R08: 0000000020006000 R09: 000000000000001c
R10: 0000000000040000 R11: 0000000000000282 R12: 00000000006e33c0
R13: 0000000000000005 R14: 0000000000000029 R15: 0000000000000023
Object at ffff880033ddd940, in cache ip_dst_cache size: 224
Allocated:
PID = 9717
 save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:59
 save_stack+0x43/0xd0 mm/kasan/kasan.c:513
 set_track mm/kasan/kasan.c:525 [inline]
 kasan_kmalloc+0xad/0xe0 mm/kasan/kasan.c:616
 kasan_slab_alloc+0x12/0x20 mm/kasan/kasan.c:555
 slab_post_alloc_hook mm/slab.h:456 [inline]
 slab_alloc_node mm/slub.c:2718 [inline]
 slab_alloc mm/slub.c:2726 [inline]
 kmem_cache_alloc+0xa8/0x160 mm/slub.c:2731
 dst_alloc+0x11b/0x1a0 net/core/dst.c:209
 rt_dst_alloc+0xf0/0x5d0 net/ipv4/route.c:1497
 __mkroute_output net/ipv4/route.c:2181 [inline]
 __ip_route_output_key_hash+0xdc4/0x2930 net/ipv4/route.c:2391
 __ip_route_output_key include/net/route.h:123 [inline]
 ip_route_output_flow+0x29/0xa0 net/ipv4/route.c:2477
 ip_route_output_key include/net/route.h:133 [inline]
 sctp_v4_get_dst+0x606/0x1420 net/sctp/protocol.c:458
 sctp_transport_route+0xa8/0x420 net/sctp/transport.c:287
 sctp_assoc_add_peer+0x5a5/0x1470 net/sctp/associola.c:656
 sctp_sendmsg+0x18a8/0x3b50 net/sctp/socket.c:1871
 inet_sendmsg+0x164/0x490 net/ipv4/af_inet.c:762
 sock_sendmsg_nosec net/socket.c:633 [inline]
 sock_sendmsg+0xca/0x110 net/socket.c:643
 SYSC_sendto+0x660/0x810 net/socket.c:1696
 SyS_sendto+0x40/0x50 net/socket.c:1664
 entry_SYSCALL_64_fastpath+0x1a/0xa9
Freed:
PID = 868
 save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:59
 save_stack+0x43/0xd0 mm/kasan/kasan.c:513
 set_track mm/kasan/kasan.c:525 [inline]
 kasan_slab_free+0x73/0xc0 mm/kasan/kasan.c:589
 slab_free_hook mm/slub.c:1357 [inline]
 slab_free_freelist_hook mm/slub.c:1379 [inline]
 slab_free mm/slub.c:2961 [inline]
 kmem_cache_free+0x72/0x190 mm/slub.c:2983
 dst_destroy+0x24c/0x390 net/core/dst.c:269
 dst_free include/net/dst.h:428 [inline]
 rt_fibinfo_free net/ipv4/fib_semantics.c:155 [inline]
 free_fib_info_rcu+0x852/0xa10 net/ipv4/fib_semantics.c:214
 __rcu_reclaim kernel/rcu/rcu.h:118 [inline]
 rcu_do_batch.isra.65+0x6de/0xbd0 kernel/rcu/tree.c:2879
 invoke_rcu_callbacks kernel/rcu/tree.c:3142 [inline]
 __rcu_process_callbacks kernel/rcu/tree.c:3109 [inline]
 rcu_process_callbacks+0x23f/0x810 kernel/rcu/tree.c:3126
 __do_softirq+0x253/0x78b kernel/softirq.c:284
Memory state around the buggy address:
 ffff880033ddd980: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffff880033ddda00: 00 00 00 00 fc fc fc fc fc fc fc fc fc fc fc fc
>ffff880033ddda80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
                                  ^
 ffff880033dddb00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff880033dddb80: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb
==================================================================


>
> Fixes: f1705ec197e7 ("net: ipv6: Make address flushing on ifdown optional")
> Reported-by: Dmitry Vyukov <dvyukov@...gle.com>
> Reported-by: Andrey Konovalov <andreyknvl@...gle.com>
> Signed-off-by: David Ahern <dsa@...ulusnetworks.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;
> +
> +               /* 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)) {
> --
> 2.1.4
>

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