netdev - Re: [PATCH net-next] virtio-net: fix use-after-free in page_to

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Date:   Tue, 20 Apr 2021 10:51:06 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Eric Dumazet <edumazet@...gle.com>
Cc:     Eric Dumazet <eric.dumazet@...il.com>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        netdev <netdev@...r.kernel.org>,
        syzbot <syzkaller@...glegroups.com>,
        Mat Martineau <mathew.j.martineau@...ux.intel.com>,
        Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
        Jason Wang <jasowang@...hat.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH net-next] virtio-net: fix use-after-free in page_to_skb()

On 4/20/21 9:31 AM, Eric Dumazet wrote:
> On Tue, Apr 20, 2021 at 5:42 PM Guenter Roeck <linux@...ck-us.net> wrote:
>>
>> On Tue, Apr 20, 2021 at 04:00:07PM +0200, Eric Dumazet wrote:
>>> On Tue, Apr 20, 2021 at 3:48 PM Guenter Roeck <linux@...ck-us.net> wrote:
>>>>
>>>> On 4/20/21 2:43 AM, Eric Dumazet wrote:
>>>
>>>>>
>>>>
>>>> Unfortunately that doesn't fix the problem for me. With this patch applied
>>>> on top of next-20210419, I still get the same crash as before:
>>>>
>>>> udhcpc: sending discover^M
>>>> Unable to handle kernel paging request at virtual address 0000000000000004^M
>>>> udhcpc(169): Oops -1^M
>>>> pc = [<0000000000000004>]  ra = [<fffffc0000b8c5b8>]  ps = 0000    Not tainted^M
>>>> pc is at 0x4^M
>>>> ra is at napi_gro_receive+0x68/0x150^M
>>>> v0 = 0000000000000000  t0 = 0000000000000008  t1 = 0000000000000000^M
>>>> t2 = 0000000000000000  t3 = 000000000000000e  t4 = 0000000000000038^M
>>>> t5 = 000000000000ffff  t6 = fffffc00002f298a  t7 = fffffc0002c78000^M
>>>> s0 = fffffc00010b3ca0  s1 = 0000000000000000  s2 = fffffc00011267e0^M
>>>> s3 = 0000000000000000  s4 = fffffc00025f2008  s5 = fffffc00002f2940^M
>>>> s6 = fffffc00025f2040^M
>>>> a0 = fffffc00025f2008  a1 = fffffc00002f2940  a2 = fffffc0002ca000c^M
>>>> a3 = fffffc00000250d0  a4 = 0000000effff0008  a5 = 0000000000000000^M
>>>> t8 = fffffc00010b3c80  t9 = fffffc0002ca04cc  t10= 0000000000000000^M
>>>> t11= 00000000000004c0  pv = fffffc0000b8bc40  at = 0000000000000000^M
>>>> gp = fffffc00010f9fb8  sp = 00000000df74db09^M
>>>> Disabling lock debugging due to kernel taint^M
>>>> Trace:^M
>>>> [<fffffc0000b8c5b8>] napi_gro_receive+0x68/0x150^M
>>>> [<fffffc00009b409c>] receive_buf+0x50c/0x1b80^M
>>>> [<fffffc00009b58b8>] virtnet_poll+0x1a8/0x5b0^M
>>>> [<fffffc00009b58ec>] virtnet_poll+0x1dc/0x5b0^M
>>>> [<fffffc0000b8d17c>] __napi_poll+0x4c/0x270^M
>>>> [<fffffc0000b8d670>] net_rx_action+0x130/0x2c0^M
>>>> [<fffffc0000bd6cb0>] sch_direct_xmit+0x170/0x360^M
>>>> [<fffffc0000bd7000>] __qdisc_run+0x160/0x6c0^M
>>>> [<fffffc0000337b64>] do_softirq+0xa4/0xd0^M
>>>> [<fffffc0000337ca4>] __local_bh_enable_ip+0x114/0x120^M
>>>> [<fffffc0000b89554>] __dev_queue_xmit+0x484/0xa60^M
>>>> [<fffffc0000cd072c>] packet_sendmsg+0xe7c/0x1ba0^M
>>>> [<fffffc0000b53338>] __sys_sendto+0xf8/0x170^M
>>>> [<fffffc0000cfec18>] _raw_spin_unlock+0x18/0x30^M
>>>> [<fffffc0000a9bf7c>] ehci_irq+0x2cc/0x5c0^M
>>>> [<fffffc0000a71334>] usb_hcd_irq+0x34/0x50^M
>>>> [<fffffc0000b521bc>] move_addr_to_kernel+0x3c/0x60^M
>>>> [<fffffc0000b532e4>] __sys_sendto+0xa4/0x170^M
>>>> [<fffffc0000b533d4>] sys_sendto+0x24/0x40^M
>>>> [<fffffc0000cfea38>] _raw_spin_lock+0x18/0x30^M
>>>> [<fffffc0000cfec18>] _raw_spin_unlock+0x18/0x30^M
>>>> [<fffffc0000325298>] clipper_enable_irq+0x98/0x100^M
>>>> [<fffffc0000cfec18>] _raw_spin_unlock+0x18/0x30^M
>>>> [<fffffc0000311514>] entSys+0xa4/0xc0^M
>>>
>>> OK, it would be nice if you could get line number from this stack trace.
>>>
>>
>> Here you are:
>>
>> napi_gro_receive (net/core/dev.c:6196)
>> receive_buf (drivers/net/virtio_net.c:1150)
>> virtnet_poll (drivers/net/virtio_net.c:1414 drivers/net/virtio_net.c:1519)
>> clipper_srm_device_interrupt (arch/alpha/kernel/sys_dp264.c:256)
>> virtnet_poll (drivers/net/virtio_net.c:1413 drivers/net/virtio_net.c:1519)
>> __napi_poll (net/core/dev.c:6962)
>> net_rx_action (net/core/dev.c:7029 net/core/dev.c:7116)
>> __qdisc_run (net/sched/sch_generic.c:376 net/sched/sch_generic.c:384)
>> do_softirq (./include/asm-generic/softirq_stack.h:10 kernel/softirq.c:460 kernel/softirq.c:447)
>> __local_bh_enable_ip (kernel/softirq.c:384)
>> __dev_queue_xmit (./include/linux/bottom_half.h:32 ./include/linux/rcupdate.h:746 net/core/dev.c:4272)
>> packet_sendmsg (net/packet/af_packet.c:3009 net/packet/af_packet.c:3034)
>> __sys_sendto (net/socket.c:654 net/socket.c:674 net/socket.c:1977)
>> __d_alloc (fs/dcache.c:1744)
>> packet_create (net/packet/af_packet.c:1192 net/packet/af_packet.c:3296)
>> move_addr_to_kernel (./include/linux/uaccess.h:192 net/socket.c:198 net/socket.c:192)
>> __sys_sendto (net/socket.c:1968)
>> sys_sendto (net/socket.c:1989 net/socket.c:1985)
>> sys_bind (net/socket.c:1648 net/socket.c:1646)
>> entSys (arch/alpha/kernel/entry.S:477)
>>
>> Guenter
> 
> OK, I guess we are back to unaligned access, right ?
> I guess sh arch should have failed as well ?
> 

sh does indeed fail, with the same symptoms as before, but so far I was not
able to track it down to a specific commit. The alpha failure is different,
though. It is a NULL pointer access.

Anyway, testing ...

The patch below does indeed fix the problem I am seeing on sh.

... and it does fix the alpha problem as well. Neat, though I don't really understand
what a NULL pointer access and an unaligned access have to do with each other.

Great catch, thanks!

Guenter


> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 8cd76037c72481200ea3e8429e9fdfec005dad85..0579914d3dd84c24982c1ff85314cc7b8d0f8d2d
> 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -415,7 +415,8 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi,
> 
>         shinfo_size = SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
> 
> -       if (len > GOOD_COPY_LEN && tailroom >= shinfo_size) {
> +       if (len > GOOD_COPY_LEN && tailroom >= shinfo_size &&
> +           (!NET_IP_ALIGN || ((unsigned long)p & 3) == 2)) {
>                 skb = build_skb(p, truesize);
>                 if (unlikely(!skb))
>                         return NULL;
>