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

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Date:   Tue, 8 Mar 2022 22:01:27 -0700
From:   David Ahern <dsahern@...nel.org>
To:     Tadeusz Struk <tadeusz.struk@...aro.org>,
        David Laight <David.Laight@...LAB.COM>,
        "davem@...emloft.net" <davem@...emloft.net>
Cc:     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 3/8/22 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.