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From:   Willem de Bruijn <willemdebruijn.kernel@gmail.com>
Date:   Thu, 10 Mar 2022 09:39:48 -0500
Message-ID: <CA+FuTSeAL7TsdW4t7=G91n3JLuYehUCnDGH4_rHS=vjm1-Nv9Q@mail.gmail.com>
Subject: Re: [PATCH] net: ipv6: fix invalid alloclen in __ip6_append_data
To:     Tadeusz Struk <tadeusz.struk@linaro.org>
Cc:     David Ahern <dsahern@kernel.org>,
        David Laight <David.Laight@aculab.com>,
        "davem@davemloft.net" <davem@davemloft.net>,
        Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>,
        Jakub Kicinski <kuba@kernel.org>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Andrii Nakryiko <andrii@kernel.org>,
        Martin KaFai Lau <kafai@fb.com>,
        Song Liu <songliubraving@fb.com>, Yonghong Song <yhs@fb.com>,
        John Fastabend <john.fastabend@gmail.com>,
        KP Singh <kpsingh@kernel.org>,
        "netdev@vger.kernel.org" <netdev@vger.kernel.org>,
        "bpf@vger.kernel.org" <bpf@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "stable@vger.kernel.org" <stable@vger.kernel.org>,
        "syzbot+e223cf47ec8ae183f2a0@syzkaller.appspotmail.com" 
        <syzbot+e223cf47ec8ae183f2a0@syzkaller.appspotmail.com>
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On Wed, Mar 9, 2022 at 4:37 PM Tadeusz Struk <tadeusz.struk@linaro.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)