Re: net: heap out-of-bounds in fib6_clean_node/rt6_fill_node/fib6_age/fib6_prune_clone

[David Ahern]

On 3/4/17 1:15 PM, Eric Dumazet wrote:
> On Sat, 2017-03-04 at 19:57 +0100, Dmitry Vyukov wrote:
>> On Fri, Mar 3, 2017 at 8:12 PM, David Ahern <dsa@xxxxxxxxxxxxxxxxxxx> wrote:
>>> On 3/3/17 6:39 AM, Dmitry Vyukov wrote:
>>>> I am getting heap out-of-bounds reports in
>>>> fib6_clean_node/rt6_fill_node/fib6_age/fib6_prune_clone while running
>>>> syzkaller fuzzer on 86292b33d4b79ee03e2f43ea0381ef85f077c760. They all
>>>> follow the same pattern: an object of size 216 is allocated from
>>>> ip_dst_cache slab, and then accessed at offset 272/276 withing
>>>> fib6_walk. Looks like type confusion. Unfortunately this is not
>>>> reproducible.
>>>
>>> I'll take a look this weekend or Monday at the latest.
>>
>>
>> I've got some additional useful info on this. I think this is
>> use-after-free rather than out-of-bounds. I've collected stack where
>> the route was disposed with call_rcu, see the last "Disposed" stack.
>> The crash happens when cmpxchg in rt_cache_route replaces an existing
>> route. And that route seems to have some existing pointers to it
>> (rt->dst.rt6_next) which fib6_walk uses to get to it after its
>> deletion.
> 
> rt_cache_route() deals with IPv4 routes.
> 
> We somehow mix IPv4 and IPv6 dsts in IPv6 tree.
> 
> We need to add type safety at IPV6 route insertions to catch the
> offender.
> 

I've seen something like this before -- a rt was on the gc list but
still linked in the tables because of some reference.

Dmitry: you seem to have reproduced this a few times. Can you share how
to run whatever tests you are using?