netdev - Re: v4.14-rc2/arm64 kernel BUG at net/core/skbuff.c:2626

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Date:   Mon, 2 Oct 2017 10:27:15 -0700
From:   Eric Dumazet <edumazet@...gle.com>
To:     Mark Rutland <mark.rutland@....com>
Cc:     Eric Dumazet <eric.dumazet@...il.com>,
        LKML <linux-kernel@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>,
        linux-arm-kernel@...ts.infradead.org,
        syzkaller <syzkaller@...glegroups.com>,
        "David S. Miller" <davem@...emloft.net>,
        Willem de Bruijn <willemb@...gle.com>
Subject: Re: v4.14-rc2/arm64 kernel BUG at net/core/skbuff.c:2626

On Mon, Oct 2, 2017 at 10:21 AM, Mark Rutland <mark.rutland@....com> wrote:
> On Mon, Oct 02, 2017 at 07:48:28AM -0700, Eric Dumazet wrote:
>> Please try the following fool proof patch.
>>
>> This is what I had in my local tree back in August but could not
>> conclude on the syzkaller bug I was working on.
>>
>> diff --git a/net/ipv4/icmp.c b/net/ipv4/icmp.c
>> index 681e33998e03b609fdca83a83e0fc62a3fee8c39..e51d777797a927058760a1ab7af00579f7488cb5 100644
>> --- a/net/ipv4/icmp.c
>> +++ b/net/ipv4/icmp.c
>> @@ -732,7 +732,8 @@ void icmp_send(struct sk_buff *skb_in, int type, int code, __be32 info)
>>               room = 576;
>>       room -= sizeof(struct iphdr) + icmp_param.replyopts.opt.opt.optlen;
>>       room -= sizeof(struct icmphdr);
>> -
>> +     if (room < 0)
>> +             goto ende;
>>       icmp_param.data_len = skb_in->len - icmp_param.offset;
>>       if (icmp_param.data_len > room)
>>               icmp_param.data_len = room;
>>
>
> Unfortuantely, with this applied I still see the issue.
>
> Syzkaller came up with a minimized reproducer [1], which can trigger the
> issue near instantly under syz-execprog. If there's anything that would
> help to narrow this down, I'm more than happy to give it a go.
>
> Thanks,
> Mark.
>
> [1] https://www.kernel.org/pub/linux/kernel/people/mark/bugs/20171002-skb_clone-misaligned-atomic/syzkaller.repro

Note that I was not trying to address the misaligned stuff.

Only this :

------------[ cut here ]------------
kernel BUG at net/core/skbuff.c:2626!
Internal error: Oops - BUG: 0 [#1] PREEMPT SMP
Modules linked in:
CPU: 3 PID: 0 Comm: swapper/3 Not tainted 4.14.0-rc2-00001-gd7ad33d #115
Hardware name: linux,dummy-virt (DT)
task: ffff80003a901a80 task.stack: ffff80003a908000
PC is at skb_copy_and_csum_bits+0x8dc/0xae0 net/core/skbuff.c:2626
LR is at skb_copy_and_csum_bits+0x8dc/0xae0 net/core/skbuff.c:2626