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Date: Wed, 21 Jul 2021 19:37:59 +0800
From: "Ziyang Xuan (William)" <william.xuanziyang@...wei.com>
To: Oliver Hartkopp <socketcan@...tkopp.net>,
Greg KH <gregkh@...uxfoundation.org>
CC: <davem@...emloft.net>, <kuba@...nel.org>, <mkl@...gutronix.de>,
<netdev@...r.kernel.org>, <linux-can@...r.kernel.org>,
<linux-kernel@...r.kernel.org>, <stable@...r.kernel.org>
Subject: Re: [PATCH net] can: raw: fix raw_rcv panic for sock UAF
On 7/21/2021 5:24 PM, Oliver Hartkopp wrote:
> 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 This kernel version 4.19.90 is definitely outdated.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@...wei.com>
>
> Can you please resend the below patch as suggested by Greg KH and add my
>
> Signed-off-by: Oliver Hartkopp <socketcan@...tkopp.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);
+
if (dev)
dev_put(dev);
release_sock(sk);
+ rtnl_unlock();
break;
@@ -600,10 +607,16 @@ 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)
+ if (ro->bound && ro->ifindex) {
dev = dev_get_by_index(sock_net(sk), ro->ifindex);
+ if (!dev) {
+ err = -ENODEV;
+ goto out_err;
+ }
+ }
/* remove current error mask */
if (ro->bound) {
@@ -627,6 +640,7 @@ static int raw_setsockopt(struct socket *sock, int level, int optname,
dev_put(dev);
release_sock(sk);
+ rtnl_unlock();
break;
>
> 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>
>>>
> .
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