netdev - Re: [PATCH net] ipv6/gro: fix an out of bounds memory bug in ipv6_gro

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Message-ID: <8523b754-992d-0d72-ecd1-4f076e57ebde@huawei.com>
Date:   Thu, 27 Oct 2022 21:00:51 +0800
From:   "Ziyang Xuan (William)" <william.xuanziyang@...wei.com>
To:     Eric Dumazet <edumazet@...gle.com>
CC:     <davem@...emloft.net>, <yoshfuji@...ux-ipv6.org>,
        <dsahern@...nel.org>, <kuba@...nel.org>, <pabeni@...hat.com>,
        <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <herbert@...dor.apana.org.au>
Subject: Re: [PATCH net] ipv6/gro: fix an out of bounds memory bug in
 ipv6_gro_receive()

> On Thu, Oct 27, 2022 at 3:25 AM Ziyang Xuan
> <william.xuanziyang@...wei.com> wrote:
>>
>> IPv6 packets without NEXTHDR_NONE extension header can make continuous
>> __skb_pull() until pskb_may_pull() failed in ipv6_gso_pull_exthdrs().
>> That results in a big value of skb_gro_offset(), and after __skb_push()
>> in ipv6_gro_receive(), skb->data will less than skb->head, an out of
>> bounds memory bug occurs. That will trigger the problem as following:
>>
>> ==================================================================
>> BUG: KASAN: use-after-free in eth_type_trans+0x100/0x260
>> ...
>> Call trace:
>>  dump_backtrace+0xd8/0x130
>>  show_stack+0x1c/0x50
>>  dump_stack_lvl+0x64/0x7c
>>  print_address_description.constprop.0+0xbc/0x2e8
>>  print_report+0x100/0x1e4
>>  kasan_report+0x80/0x120
>>  __asan_load8+0x78/0xa0
>>  eth_type_trans+0x100/0x260
> 
> Crash happens from eth_type_trans() , this should happen before
> ipv6_gro_receive() ?
> 
> It seems your patch is unrelated.
> 
> Please provide a repro.

C repro put in attachment.

> 
> 
>>  napi_gro_frags+0x164/0x550
>>  tun_get_user+0xda4/0x1270
>>  tun_chr_write_iter+0x74/0x130
>>  do_iter_readv_writev+0x130/0x1ec
>>  do_iter_write+0xbc/0x1e0
>>  vfs_writev+0x13c/0x26c
>>
>> Add comparison between skb->data - skb_gro_offset() and skb->head
>> and exception handler before __skb_push() to fix the bug.
>>
>> Fixes: 86911732d399 ("gro: Avoid copying headers of unmerged packets")
>> Signed-off-by: Ziyang Xuan <william.xuanziyang@...wei.com>
>> ---
>>  net/ipv6/ip6_offload.c | 4 ++++
>>  1 file changed, 4 insertions(+)
>>
>> diff --git a/net/ipv6/ip6_offload.c b/net/ipv6/ip6_offload.c
>> index 3ee345672849..6659ccf25387 100644
>> --- a/net/ipv6/ip6_offload.c
>> +++ b/net/ipv6/ip6_offload.c
>> @@ -237,6 +237,10 @@ INDIRECT_CALLABLE_SCOPE struct sk_buff *ipv6_gro_receive(struct list_head *head,
>>                 proto = ipv6_gso_pull_exthdrs(skb, proto);
>>                 skb_gro_pull(skb, -skb_transport_offset(skb));
>>                 skb_reset_transport_header(skb);
>> +               if (unlikely(skb_headroom(skb) < skb_gro_offset(skb))) {
> 
> This makes no sense to me.
> 
> If there is a bug, it should be fixed earlier.

Maybe it is good to validate IPv6 packet earlier in ipv6_gro_receive() or more earlier?

> 
>> +                       kfree_skb(skb);
>> +                       return ERR_PTR(-EINPROGRESS);
>> +               }
>>                 __skb_push(skb, skb_gro_offset(skb));
>>
>>                 ops = rcu_dereference(inet6_offloads[proto]);
>> --
>> 2.25.1
>>
> .
> 

View attachment "eth_type_trans_uaf.c" of type "text/plain" (19213 bytes)