Re: [PATCH] net: ipv6: fix invalid alloclen in __ip6_append_data

[Tadeusz Struk]

On 3/10/22 06:39, Willem de Bruijn wrote:
> On Wed, Mar 9, 2022 at 4:37 PM Tadeusz Struk <tadeusz.struk@xxxxxxxxxx> 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