diff mbox series

[net] can: raw: fix raw_rcv panic for sock UAF

Message ID 20210721010937.670275-1-william.xuanziyang@huawei.com
State New
Headers show
Series [net] can: raw: fix raw_rcv panic for sock UAF | expand

Commit Message

Ziyang Xuan July 21, 2021, 1:09 a.m. UTC 
We get a bug during ltp can_filter test as following.

Comments

Ziyang Xuan July 22, 2021, 7:06 a.m. UTC | #1 
On 7/21/2021 11:13 PM, Oliver Hartkopp wrote:
> 
> 
> On 21.07.21 13:37, Ziyang Xuan (William) wrote:
>> On 7/21/2021 5:24 PM, Oliver Hartkopp wrote:
> 
>>>
>>> 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;
>>> +        }
>> At first, I also use this modification. After discussion with my partner, we found that
>> it is impossible scenario if we use rtnl_lock to protect net_device object.
>> We can see two sequences:
>> 1. raw_setsockopt first get rtnl_lock, unregister_netdevice_many later.
>> It can be simplified to add the filter in raw_setsockopt, then remove the filter in raw_notify.
>>
>> 2. unregister_netdevice_many first get rtnl_lock, raw_setsockopt later.
>> raw_notify will set ro->ifindex, ro->bound and ro->count to zero firstly. The filter will not
>> be added to any filter_list in raw_notify.
>>
>> So I selected the current modification. Do you think so?
>>
>> My first modification as following:
>>
>> diff --git a/net/can/raw.c b/net/can/raw.c
>> index ed4fcb7ab0c3..a0ce4908317f 100644
>> --- a/net/can/raw.c
>> +++ b/net/can/raw.c
>> @@ -546,10 +546,16 @@ static int raw_setsockopt(struct socket *sock, int level, int optname,
>>                                  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) {
>> +                               err = -ENODEV;
>> +                               goto out_fil;
>> +                       }
>> +               }
>>
>>                  if (ro->bound) {
>>                          /* (try to) register the new filters */
>> @@ -559,11 +565,8 @@ static int raw_setsockopt(struct socket *sock, int level, int optname,
>>                          else
>>                                  err = raw_enable_filters(sock_net(sk), dev, sk,
>>                                                           filter, count);
>> -                       if (err) {
>> -                               if (count > 1)
>> -                                       kfree(filter);
>> +                       if (err)
>>                                  goto out_fil;
>> -                       }
>>
>>                          /* remove old filter registrations */
>>                          raw_disable_filters(sock_net(sk), dev, sk, ro->filter,
>> @@ -584,10 +587,14 @@ static int raw_setsockopt(struct socket *sock, int level, int optname,
>>                  ro->count  = count;
>>
>>    out_fil:
>> +               if (err && count > 1)
>> +                       kfree(filter);
>> +
> 
> Setting the err variable to -ENODEV is a good idea but I do not like the movement of kfree(filter).
> 
> The kfree() has a tight relation inside the if-statement for ro->bound which makes it easier to understand.
> 
> Regards,
> Oliver

I will submit the v2 patch for the problem according to your suggestions. Than you.
diff mbox series

Patch

===========================================
[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
[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. 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>
---
 net/can/raw.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/net/can/raw.c b/net/can/raw.c
index ed4fcb7ab0c3..a63e9915c66a 100644
--- a/net/can/raw.c
+++ b/net/can/raw.c
@@ -546,6 +546,7 @@  static int raw_setsockopt(struct socket *sock, int level, int optname,
 				return -EFAULT;
 		}
 
+		rtnl_lock();
 		lock_sock(sk);
 
 		if (ro->bound && ro->ifindex)
@@ -588,6 +589,7 @@  static int raw_setsockopt(struct socket *sock, int level, int optname,
 			dev_put(dev);
 
 		release_sock(sk);
+		rtnl_unlock();
 
 		break;
 
@@ -600,6 +602,7 @@  static int raw_setsockopt(struct socket *sock, int level, int optname,
 
 		err_mask &= CAN_ERR_MASK;
 
+		rtnl_lock();
 		lock_sock(sk);
 
 		if (ro->bound && ro->ifindex)
@@ -627,6 +630,7 @@  static int raw_setsockopt(struct socket *sock, int level, int optname,
 			dev_put(dev);
 
 		release_sock(sk);
+		rtnl_unlock();
 
 		break;