netdev - Re: [PATCH] net: ipv6: fix invalid alloclen in __ip6_append

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Message-ID: <c7608cf0-fda2-1aa6-b0c1-3d4e0b5cad0e@linaro.org>
Date:   Thu, 10 Mar 2022 08:06:15 -0800
From:   Tadeusz Struk <tadeusz.struk@...aro.org>
To:     Willem de Bruijn <willemdebruijn.kernel@...il.com>
Cc:     David Ahern <dsahern@...nel.org>,
        David Laight <David.Laight@...lab.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        Jakub Kicinski <kuba@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        "syzbot+e223cf47ec8ae183f2a0@...kaller.appspotmail.com" 
        <syzbot+e223cf47ec8ae183f2a0@...kaller.appspotmail.com>
Subject: Re: [PATCH] net: ipv6: fix invalid alloclen in __ip6_append_data

On 3/10/22 06:39, Willem de Bruijn wrote:
> On Wed, Mar 9, 2022 at 4:37 PM Tadeusz Struk <tadeusz.struk@...aro.org> wrote:
>>
>> On 3/8/22 21:01, David Ahern wrote:
>>> On 3/8/22 12:46 PM, Tadeusz Struk wrote:
>>>> That fails in the same way:
>>>>
>>>> skbuff: skb_over_panic: text:ffffffff83e7b48b len:65575 put:65575
>>>> head:ffff888101f8a000 data:ffff888101f8a088 tail:0x100af end:0x6c0
>>>> dev:<NULL>
>>>> ------------[ cut here ]------------
>>>> kernel BUG at net/core/skbuff.c:113!
>>>> invalid opcode: 0000 [#1] PREEMPT SMP KASAN
>>>> CPU: 0 PID: 1852 Comm: repro Not tainted
>>>> 5.17.0-rc7-00020-gea4424be1688-dirty #19
>>>> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1.fc35
>>>> RIP: 0010:skb_panic+0x173/0x175
>>>>
>>>> I'm not sure how it supposed to help since it doesn't change the
>>>> alloclen at all.
>>>
>>> alloclen is a function of fraglen and fraglen is a function of datalen.
>>
>> Ok, but in this case it doesn't affect the alloclen and it still fails.
> 
> This is some kind of non-standard packet that is being constructed. Do
> we understand how it is different?
> 
> The .syz reproducer is generally a bit more readable than the .c
> equivalent. Though not as much as an strace of the binary, if you
> can share that.
> 
> r0 = socket$inet6_icmp_raw(0xa, 0x3, 0x3a)
> connect$inet6(r0, &(0x7f0000000040)={0xa, 0x0, 0x0, @dev, 0x6}, 0x1c)
> setsockopt$inet6_IPV6_HOPOPTS(r0, 0x29, 0x36,
> &(0x7f0000000100)=ANY=[@ANYBLOB="52b3"], 0x5a0)
> sendmmsg$inet(r0, &(0x7f00000002c0)=[{{0x0, 0x0,
> &(0x7f0000000000)=[{&(0x7f00000000c0)="1d2d", 0xfa5f}], 0x1}}], 0x1,
> 0xfe80)

Here it is:
https://termbin.com/krtr
It won't be of much help, I'm afraid, as the offending sendmmsg()
call isn't fully printed.

-- 
Thanks,
Tadeusz