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Subject: Re: [PATCH net] can: raw: fix raw_rcv panic for sock UAF
From:   Oliver Hartkopp <socketcan@hartkopp.net>
To:     Greg KH <gregkh@linuxfoundation.org>,
        Ziyang Xuan <william.xuanziyang@huawei.com>
Cc:     davem@davemloft.net, kuba@kernel.org, mkl@pengutronix.de,
        netdev@vger.kernel.org, linux-can@vger.kernel.org,
        linux-kernel@vger.kernel.org, stable@vger.kernel.org
References: <20210721010937.670275-1-william.xuanziyang@huawei.com>
 <YPeoQG19PSh3B3Dc@kroah.com>
 <44c3e0e2-03c5-80e5-001c-03e7e9758bca@hartkopp.net>
Message-ID: <11822417-5931-b2d8-ae77-ec4a84b8b895@hartkopp.net>
Date:   Wed, 21 Jul 2021 11:24:20 +0200
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Answering myself ...

On 21.07.21 08:35, Oliver Hartkopp wrote:
> 
> 
> On 21.07.21 06:53, Greg KH wrote:
>> On Wed, Jul 21, 2021 at 09:09:37AM +0800, Ziyang Xuan wrote:
>>> We get a bug during ltp can_filter test as following.
>>>
>>> ===========================================
>>> [60919.264984] BUG: unable to handle kernel NULL pointer dereference 
>>> at 0000000000000010
>>> [60919.265223] PGD 8000003dda726067 P4D 8000003dda726067 PUD 
>>> 3dda727067 PMD 0
>>> [60919.265443] Oops: 0000 [#1] SMP PTI
>>> [60919.265550] CPU: 30 PID: 3638365 Comm: can_filter Kdump: loaded 
>>> Tainted: G        W         4.19.90+ #1
> 
> This kernel version 4.19.90 is definitely outdated.
> 
> Can you please check your issue with the latest uptream kernel as this 
> problem should have been fixed with this patch:
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=8d0caedb759683041d9db82069937525999ada53 
> 
> ("can: bcm/raw/isotp: use per module netdevice notifier")
> 
> Thanks!

I think my hint had a wrong assumption. The suggestion to add some 
locking seems correct.

>>> [60919.266068] RIP: 0010:selinux_socket_sock_rcv_skb+0x3e/0x200
>>> [60919.293289] RSP: 0018:ffff8d53bfc03cf8 EFLAGS: 00010246
>>> [60919.307140] RAX: 0000000000000000 RBX: 000000000000001d RCX: 
>>> 0000000000000007
>>> [60919.320756] RDX: 0000000000000001 RSI: ffff8d5104a8ed00 RDI: 
>>> ffff8d53bfc03d30
>>> [60919.334319] RBP: ffff8d9338056800 R08: ffff8d53bfc29d80 R09: 
>>> 0000000000000001
>>> [60919.347969] R10: ffff8d53bfc03ec0 R11: ffffb8526ef47c98 R12: 
>>> ffff8d53bfc03d30
>>> [60919.350320] perf: interrupt took too long (3063 > 2500), lowering 
>>> kernel.perf_event_max_sample_rate to 65000
>>> [60919.361148] R13: 0000000000000001 R14: ffff8d53bcf90000 R15: 
>>> 0000000000000000
>>> [60919.361151] FS:  00007fb78b6b3600(0000) GS:ffff8d53bfc00000(0000) 
>>> knlGS:0000000000000000
>>> [60919.400812] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>>> [60919.413730] CR2: 0000000000000010 CR3: 0000003e3f784006 CR4: 
>>> 00000000007606e0
>>> [60919.426479] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 
>>> 0000000000000000
>>> [60919.439339] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 
>>> 0000000000000400
>>> [60919.451608] PKRU: 55555554
>>> [60919.463622] Call Trace:
>>> [60919.475617]  <IRQ>
>>> [60919.487122]  ? update_load_avg+0x89/0x5d0
>>> [60919.498478]  ? update_load_avg+0x89/0x5d0
>>> [60919.509822]  ? account_entity_enqueue+0xc5/0xf0
>>> [60919.520709]  security_sock_rcv_skb+0x2a/0x40
>>> [60919.531413]  sk_filter_trim_cap+0x47/0x1b0
>>> [60919.542178]  ? kmem_cache_alloc+0x38/0x1b0
>>> [60919.552444]  sock_queue_rcv_skb+0x17/0x30
>>> [60919.562477]  raw_rcv+0x110/0x190 [can_raw]
>>> [60919.572539]  can_rcv_filter+0xbc/0x1b0 [can]
>>> [60919.582173]  can_receive+0x6b/0xb0 [can]
>>> [60919.591595]  can_rcv+0x31/0x70 [can]
>>> [60919.600783]  __netif_receive_skb_one_core+0x5a/0x80
>>> [60919.609864]  process_backlog+0x9b/0x150
>>> [60919.618691]  net_rx_action+0x156/0x400
>>> [60919.627310]  ? sched_clock_cpu+0xc/0xa0
>>> [60919.635714]  __do_softirq+0xe8/0x2e9
>>> [60919.644161]  do_softirq_own_stack+0x2a/0x40
>>> [60919.652154]  </IRQ>
>>> [60919.659899]  do_softirq.part.17+0x4f/0x60
>>> [60919.667475]  __local_bh_enable_ip+0x60/0x70
>>> [60919.675089]  __dev_queue_xmit+0x539/0x920
>>> [60919.682267]  ? finish_wait+0x80/0x80
>>> [60919.689218]  ? finish_wait+0x80/0x80
>>> [60919.695886]  ? sock_alloc_send_pskb+0x211/0x230
>>> [60919.702395]  ? can_send+0xe5/0x1f0 [can]
>>> [60919.708882]  can_send+0xe5/0x1f0 [can]
>>> [60919.715037]  raw_sendmsg+0x16d/0x268 [can_raw]
>>>
>>> It's because raw_setsockopt() concurrently with
>>> unregister_netdevice_many(). Concurrent scenario as following.
>>>
>>>     cpu0                        cpu1
>>> raw_bind
>>> raw_setsockopt                    unregister_netdevice_many
>>>                         unlist_netdevice
>>> dev_get_by_index                raw_notifier
>>> raw_enable_filters                ......
>>> can_rx_register
>>> can_rcv_list_find(..., net->can.rx_alldev_list)
>>>
>>> ......
>>>
>>> sock_close
>>> raw_release(sock_a)
>>>
>>> ......
>>>
>>> can_receive
>>> can_rcv_filter(net->can.rx_alldev_list, ...)
>>> raw_rcv(skb, sock_a)
>>> BUG
>>>
>>> After unlist_netdevice(), dev_get_by_index() return NULL in
>>> raw_setsockopt(). Function raw_enable_filters() will add sock
>>> and can_filter to net->can.rx_alldev_list.

Btw. this should not happen too!

dev_get_by_index() is executed depending on ro->ifindex which means 
there should be a real network interface. When dev_get_by_index() 
returns NULL this can considered to be wrong.

Adding a new filter to net->can.rx_alldev_list as a consequence is wrong 
too.

>>> Then the sock is closed.
>>> Followed by, we sock_sendmsg() to a new vcan device use the same
>>> can_filter. Protocol stack match the old receiver whose sock has
>>> been released on net->can.rx_alldev_list in can_rcv_filter().
>>> Function raw_rcv() uses the freed sock. UAF BUG is triggered.
>>>
>>> We can find that the key issue is that net_device has not been
>>> protected in raw_setsockopt(). Use rtnl_lock to protect net_device
>>> in raw_setsockopt().
>>>
>>> Fixes: c18ce101f2e4 ("[CAN]: Add raw protocol")
>>> Signed-off-by: Ziyang Xuan <william.xuanziyang@huawei.com>

Can you please resend the below patch as suggested by Greg KH and add my

Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>

as it also adds the dev_get_by_index() return check.

diff --git a/net/can/raw.c b/net/can/raw.c
index ed4fcb7ab0c3..d3cbc32036c7 100644
--- a/net/can/raw.c
+++ b/net/can/raw.c
@@ -544,14 +544,18 @@ static int raw_setsockopt(struct socket *sock, int 
level, int optname,
  		} else if (count == 1) {
  			if (copy_from_sockptr(&sfilter, optval, sizeof(sfilter)))
  				return -EFAULT;
  		}

+		rtnl_lock();
  		lock_sock(sk);

-		if (ro->bound && ro->ifindex)
+		if (ro->bound && ro->ifindex) {
  			dev = dev_get_by_index(sock_net(sk), ro->ifindex);
+			if (!dev)
+				goto out_fil;
+		}

  		if (ro->bound) {
  			/* (try to) register the new filters */
  			if (count == 1)
  				err = raw_enable_filters(sock_net(sk), dev, sk,
@@ -586,10 +590,11 @@ static int raw_setsockopt(struct socket *sock, int 
level, int optname,
   out_fil:
  		if (dev)
  			dev_put(dev);

  		release_sock(sk);
+		rtnl_unlock();

  		break;

  	case CAN_RAW_ERR_FILTER:
  		if (optlen != sizeof(err_mask))
@@ -598,14 +603,18 @@ static int raw_setsockopt(struct socket *sock, int 
level, int optname,
  		if (copy_from_sockptr(&err_mask, optval, optlen))
  			return -EFAULT;

  		err_mask &= CAN_ERR_MASK;

+		rtnl_lock();
  		lock_sock(sk);

-		if (ro->bound && ro->ifindex)
+		if (ro->bound && ro->ifindex) {
  			dev = dev_get_by_index(sock_net(sk), ro->ifindex);
+			if (!dev)
+				goto out_err;
+		}

  		/* remove current error mask */
  		if (ro->bound) {
  			/* (try to) register the new err_mask */
  			err = raw_enable_errfilter(sock_net(sk), dev, sk,
@@ -625,10 +634,11 @@ static int raw_setsockopt(struct socket *sock, int 
level, int optname,
   out_err:
  		if (dev)
  			dev_put(dev);

  		release_sock(sk);
+		rtnl_unlock();

  		break;

  	case CAN_RAW_LOOPBACK:
  		if (optlen != sizeof(ro->loopback))


Thanks for the finding!

Best regards,
Oliver

(..)
>>
>>
>> <formletter>
>>
>> This is not the correct way to submit patches for inclusion in the
>> stable kernel tree.  Please read:
>>      
>> https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html
>> for how to do this properly.
>>
>> </formletter>
>>