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Subject: Re: [PATCH net] can: raw: fix raw_rcv panic for sock UAF
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>
From:   Oliver Hartkopp <socketcan@hartkopp.net>
Message-ID: <44c3e0e2-03c5-80e5-001c-03e7e9758bca@hartkopp.net>
Date:   Wed, 21 Jul 2021 08:35:45 +0200
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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This kernel version 4.19.90 is definitely outdated.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!

>> [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;
>>   
>> -- 
>> 2.25.1
>>
> 
> 
> <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>
>