netdev - Re: [PATCH net] ipv6: don't let tb6_root node share routes with other node

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Date:   Thu, 18 Jan 2018 15:31:29 -0800
From:   Wei Wang <weiwan@...gle.com>
To:     Martin KaFai Lau <kafai@...com>
Cc:     David Miller <davem@...emloft.net>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>
Subject: Re: [PATCH net] ipv6: don't let tb6_root node share routes with other node

On Thu, Jan 18, 2018 at 2:47 PM, Martin KaFai Lau <kafai@...com> wrote:
> On Thu, Jan 18, 2018 at 10:40:03AM -0800, Wei Wang wrote:
>> From: Wei Wang <weiwan@...gle.com>
>>
>> After commit 4512c43eac7e, if we add a route to the subtree of tb6_root
>> which does not have any route attached to it yet, the current code will
>> let tb6_root and the node in the subtree share the same route.
>> This could cause problem cause tb6_root has RTN_INFO flag marked and the
> You meant the RTN_RTINFO check in fib6_purge_rt()?
>
Yes. Exactly.

>> tree repair and clean up code will not work properly.
>> This commit makes sure tb6_root->leaf points back to null_entry instead
>> of sharing route with other node.
>>
>> It fixes the following syzkaller reported issue:
>> BUG: KASAN: use-after-free in ipv6_prefix_equal include/net/ipv6.h:540 [inline]
>> BUG: KASAN: use-after-free in fib6_add_1+0x165f/0x1790 net/ipv6/ip6_fib.c:618
>> Read of size 8 at addr ffff8801bc043498 by task syz-executor5/19819
>>
>> CPU: 1 PID: 19819 Comm: syz-executor5 Not tainted 4.15.0-rc7+ #186
>> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
>> Call Trace:
>>  __dump_stack lib/dump_stack.c:17 [inline]
>>  dump_stack+0x194/0x257 lib/dump_stack.c:53
>>  print_address_description+0x73/0x250 mm/kasan/report.c:252
>>  kasan_report_error mm/kasan/report.c:351 [inline]
>>  kasan_report+0x25b/0x340 mm/kasan/report.c:409
>>  __asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:430
>>  ipv6_prefix_equal include/net/ipv6.h:540 [inline]
>>  fib6_add_1+0x165f/0x1790 net/ipv6/ip6_fib.c:618
>>  fib6_add+0x5fa/0x1540 net/ipv6/ip6_fib.c:1214
>>  __ip6_ins_rt+0x6c/0x90 net/ipv6/route.c:1003
>>  ip6_route_add+0x141/0x190 net/ipv6/route.c:2790
>>  ipv6_route_ioctl+0x4db/0x6b0 net/ipv6/route.c:3299
>>  inet6_ioctl+0xef/0x1e0 net/ipv6/af_inet6.c:520
>>  sock_do_ioctl+0x65/0xb0 net/socket.c:958
>>  sock_ioctl+0x2c2/0x440 net/socket.c:1055
>>  vfs_ioctl fs/ioctl.c:46 [inline]
>>  do_vfs_ioctl+0x1b1/0x1520 fs/ioctl.c:686
>>  SYSC_ioctl fs/ioctl.c:701 [inline]
>>  SyS_ioctl+0x8f/0xc0 fs/ioctl.c:692
>>  entry_SYSCALL_64_fastpath+0x23/0x9a
>> RIP: 0033:0x452ac9
>> RSP: 002b:00007fd42b321c58 EFLAGS: 00000212 ORIG_RAX: 0000000000000010
>> RAX: ffffffffffffffda RBX: 000000000071bea0 RCX: 0000000000452ac9
>> RDX: 0000000020fd7000 RSI: 000000000000890b RDI: 0000000000000013
>> RBP: 000000000000049e R08: 0000000000000000 R09: 0000000000000000
>> R10: 0000000000000000 R11: 0000000000000212 R12: 00000000006f4f70
>> R13: 00000000ffffffff R14: 00007fd42b3226d4 R15: 0000000000000000
>>
>> Fixes: 4512c43eac7e ("ipv6: remove null_entry before adding default route")
>> Signed-off-by: Wei Wang <weiwan@...gle.com>
>> Acked-by: Eric Dumazet <edumazet@...gle.com>
>> ---
>>  net/ipv6/ip6_fib.c | 10 ++++++++--
>>  1 file changed, 8 insertions(+), 2 deletions(-)
>>
>> diff --git a/net/ipv6/ip6_fib.c b/net/ipv6/ip6_fib.c
>> index 9dcc3924a975..217683d40f12 100644
>> --- a/net/ipv6/ip6_fib.c
>> +++ b/net/ipv6/ip6_fib.c
>> @@ -1226,8 +1226,14 @@ int fib6_add(struct fib6_node *root, struct rt6_info *rt,
>>               }
>>
>>               if (!rcu_access_pointer(fn->leaf)) {
>> -                     atomic_inc(&rt->rt6i_ref);
>> -                     rcu_assign_pointer(fn->leaf, rt);
>> +                     if (fn->fn_flags & RTN_TL_ROOT) {
>> +                             /* put back null_entry for root node */
>> +                             rcu_assign_pointer(fn->leaf,
>> +                                         info->nl_net->ipv6.ip6_null_entry);
>> +                     } else {
>> +                             atomic_inc(&rt->rt6i_ref);
>> +                             rcu_assign_pointer(fn->leaf, rt);
>> +                     }
>>               }
>>               fn = sn;
>>       }
>> --
>> 2.16.0.rc1.238.g530d649a79-goog
>>