[PATCH v4] net: rose: fix null-ptr-deref caused by rose_kill_by_neigh

[PATCH v4] net: rose: fix null-ptr-deref caused by rose_kill_by_neigh

[Duoming Zhou]

When the link layer connection is broken, the rose->neighbour is
set to null. But rose->neighbour could be used by rose_connection()
and rose_release() later, because there is no synchronization among
them. As a result, the null-ptr-deref bugs will happen.

One of the null-ptr-deref bugs is shown below:

    (thread 1)                  |        (thread 2)
                                |  rose_connect
rose_kill_by_neigh              |    lock_sock(sk)
  spin_lock_bh(&rose_list_lock) |    if (!rose->neighbour)
  rose->neighbour = NULL;//(1)  |
                                |    rose->neighbour->use++;//(2)

The rose->neighbour is set to null in position (1) and dereferenced
in position (2).

The KASAN report triggered by POC is shown below:

KASAN: null-ptr-deref in range [0x0000000000000028-0x000000000000002f]
...
RIP: 0010:rose_connect+0x6c2/0xf30
RSP: 0018:ffff88800ab47d60 EFLAGS: 00000206
RAX: 0000000000000005 RBX: 000000000000002a RCX: 0000000000000000
RDX: ffff88800ab38000 RSI: ffff88800ab47e48 RDI: ffff88800ab38309
RBP: dffffc0000000000 R08: 0000000000000000 R09: ffffed1001567062
R10: dfffe91001567063 R11: 1ffff11001567061 R12: 1ffff11000d17cd0
R13: ffff8880068be680 R14: 0000000000000002 R15: 1ffff11000d17cd0
...
Call Trace:
  <TASK>
  ? __local_bh_enable_ip+0x54/0x80
  ? selinux_netlbl_socket_connect+0x26/0x30
  ? rose_bind+0x5b0/0x5b0
  __sys_connect+0x216/0x280
  __x64_sys_connect+0x71/0x80
  do_syscall_64+0x43/0x90
  entry_SYSCALL_64_after_hwframe+0x46/0xb0

This patch adds lock_sock() in rose_kill_by_neigh() in order to
synchronize with rose_connect() and rose_release().

Meanwhile, this patch adds sock_hold() protected by rose_list_lock
that could synchronize with rose_remove_socket() in order to mitigate
UAF bug caused by lock_sock() we add.

What's more, there is no need using rose_neigh_list_lock to protect
rose_kill_by_neigh(). Because we have already used rose_neigh_list_lock
to protect the state change of rose_neigh in rose_link_failed(), which
is well synchronized.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Duoming Zhou <duoming@zju.edu.cn>
---
Changes in v4:
  - v4: Fix traversing erroneously stop problem.

 net/rose/af_rose.c    | 8 ++++++++
 net/rose/rose_route.c | 2 ++
 2 files changed, 10 insertions(+)

diff --git a/net/rose/af_rose.c b/net/rose/af_rose.c
index bf2d986a6bc..24dcbde88fb 100644
--- a/net/rose/af_rose.c
+++ b/net/rose/af_rose.c
@@ -165,13 +165,21 @@ void rose_kill_by_neigh(struct rose_neigh *neigh)
 	struct sock *s;
 
 	spin_lock_bh(&rose_list_lock);
+again:
 	sk_for_each(s, &rose_list) {
 		struct rose_sock *rose = rose_sk(s);
 
 		if (rose->neighbour == neigh) {
+			sock_hold(s);
+			spin_unlock_bh(&rose_list_lock);
+			lock_sock(s);
 			rose_disconnect(s, ENETUNREACH, ROSE_OUT_OF_ORDER, 0);
 			rose->neighbour->use--;
 			rose->neighbour = NULL;
+			release_sock(s);
+			spin_lock_bh(&rose_list_lock);
+			sock_put(s);
+			goto again;
 		}
 	}
 	spin_unlock_bh(&rose_list_lock);
diff --git a/net/rose/rose_route.c b/net/rose/rose_route.c
index fee6409c2bb..b116828b422 100644
--- a/net/rose/rose_route.c
+++ b/net/rose/rose_route.c
@@ -827,7 +827,9 @@ void rose_link_failed(ax25_cb *ax25, int reason)
 		ax25_cb_put(ax25);
 
 		rose_del_route_by_neigh(rose_neigh);
+		spin_unlock_bh(&rose_neigh_list_lock);
 		rose_kill_by_neigh(rose_neigh);
+		return;
 	}
 	spin_unlock_bh(&rose_neigh_list_lock);
 }
-- 
2.17.1

Re: [PATCH v4] net: rose: fix null-ptr-deref caused by rose_kill_by_neigh

[Jakub Kicinski]

On Wed, 29 Jun 2022 18:49:41 +0800 Duoming Zhou wrote:
> When the link layer connection is broken, the rose->neighbour is
> set to null. But rose->neighbour could be used by rose_connection()
> and rose_release() later, because there is no synchronization among
> them. As a result, the null-ptr-deref bugs will happen.
> 
> One of the null-ptr-deref bugs is shown below:
> 
>     (thread 1)                  |        (thread 2)
>                                 |  rose_connect
> rose_kill_by_neigh              |    lock_sock(sk)
>   spin_lock_bh(&rose_list_lock) |    if (!rose->neighbour)
>   rose->neighbour = NULL;//(1)  |
>                                 |    rose->neighbour->use++;//(2)

>  		if (rose->neighbour == neigh) {

Why is it okay to perform this comparison without the socket lock,
if we need a socket lock to clear it? Looks like rose_kill_by_neigh()
is not guaranteed to clear all the uses of a neighbor.

> +			sock_hold(s);
> +			spin_unlock_bh(&rose_list_lock);
> +			lock_sock(s);
>  			rose_disconnect(s, ENETUNREACH, ROSE_OUT_OF_ORDER, 0);
>  			rose->neighbour->use--;

What protects the use counter?

>  			rose->neighbour = NULL;
> +			release_sock(s);
> +			spin_lock_bh(&rose_list_lock);

Don't take the lock here just dump one line further back.

> +			sock_put(s);
> +			goto again;
>  		}
>  	}
>  	spin_unlock_bh(&rose_list_lock);
> diff --git a/net/rose/rose_route.c b/net/rose/rose_route.c
> index fee6409c2bb..b116828b422 100644
> --- a/net/rose/rose_route.c
> +++ b/net/rose/rose_route.c
> @@ -827,7 +827,9 @@ void rose_link_failed(ax25_cb *ax25, int reason)
>  		ax25_cb_put(ax25);
>  
>  		rose_del_route_by_neigh(rose_neigh);
> +		spin_unlock_bh(&rose_neigh_list_lock);
>  		rose_kill_by_neigh(rose_neigh);
> +		return;
>  	}
>  	spin_unlock_bh(&rose_neigh_list_lock);
>  }

Re: [PATCH v4] net: rose: fix null-ptr-deref caused by rose_kill_by_neigh

[duoming]

Hello,

On Fri, 1 Jul 2022 19:41:55 -0700 Jakub Kicinski wrote:

> On Wed, 29 Jun 2022 18:49:41 +0800 Duoming Zhou wrote:
> > When the link layer connection is broken, the rose->neighbour is
> > set to null. But rose->neighbour could be used by rose_connection()
> > and rose_release() later, because there is no synchronization among
> > them. As a result, the null-ptr-deref bugs will happen.
> > 
> > One of the null-ptr-deref bugs is shown below:
> > 
> >     (thread 1)                  |        (thread 2)
> >                                 |  rose_connect
> > rose_kill_by_neigh              |    lock_sock(sk)
> >   spin_lock_bh(&rose_list_lock) |    if (!rose->neighbour)
> >   rose->neighbour = NULL;//(1)  |
> >                                 |    rose->neighbour->use++;//(2)
> 
> >  		if (rose->neighbour == neigh) {
> 
> Why is it okay to perform this comparison without the socket lock,
> if we need a socket lock to clear it? Looks like rose_kill_by_neigh()
> is not guaranteed to clear all the uses of a neighbor.

I am sorry, the comparision should also be protected with socket lock.
The rose_kill_by_neigh() only clear the neighbor that is passed as
parameter of rose_kill_by_neigh(). 

> > +			sock_hold(s);
> > +			spin_unlock_bh(&rose_list_lock);
> > +			lock_sock(s);
> >  			rose_disconnect(s, ENETUNREACH, ROSE_OUT_OF_ORDER, 0);
> >  			rose->neighbour->use--;
> 
> What protects the use counter?

The use coounter is protected by socket lock.

> >  			rose->neighbour = NULL;
> > +			release_sock(s);
> > +			spin_lock_bh(&rose_list_lock);
> 
> Don't take the lock here just dump one line further back.

Ok, I will dump one line further back.

Best regards,
Duoming Zhou

Re: [PATCH v4] net: rose: fix null-ptr-deref caused by rose_kill_by_neigh

[Jakub Kicinski]

On Sat, 2 Jul 2022 15:23:57 +0800 (GMT+08:00) duoming@zju.edu.cn wrote:
> > On Wed, 29 Jun 2022 18:49:41 +0800 Duoming Zhou wrote:  
> > > When the link layer connection is broken, the rose->neighbour is
> > > set to null. But rose->neighbour could be used by rose_connection()
> > > and rose_release() later, because there is no synchronization among
> > > them. As a result, the null-ptr-deref bugs will happen.
> > > 
> > > One of the null-ptr-deref bugs is shown below:
> > > 
> > >     (thread 1)                  |        (thread 2)
> > >                                 |  rose_connect
> > > rose_kill_by_neigh              |    lock_sock(sk)
> > >   spin_lock_bh(&rose_list_lock) |    if (!rose->neighbour)
> > >   rose->neighbour = NULL;//(1)  |
> > >                                 |    rose->neighbour->use++;//(2)  
> >   
> > >  		if (rose->neighbour == neigh) {  
> > 
> > Why is it okay to perform this comparison without the socket lock,
> > if we need a socket lock to clear it? Looks like rose_kill_by_neigh()
> > is not guaranteed to clear all the uses of a neighbor.  
> 
> I am sorry, the comparision should also be protected with socket lock.
> The rose_kill_by_neigh() only clear the neighbor that is passed as
> parameter of rose_kill_by_neigh(). 

Don't think that's possible, you'd have to drop the neigh lock every
time.

> > > +			sock_hold(s);
> > > +			spin_unlock_bh(&rose_list_lock);
> > > +			lock_sock(s);
> > >  			rose_disconnect(s, ENETUNREACH, ROSE_OUT_OF_ORDER, 0);
> > >  			rose->neighbour->use--;  
> > 
> > What protects the use counter?  
> 
> The use coounter is protected by socket lock.

Which one, the neigh object can be shared by multiple sockets, no?

Re: [PATCH v4] net: rose: fix null-ptr-deref caused by rose_kill_by_neigh

[duoming]

Hello,

On Sat, 2 Jul 2022 12:01:08 -0700 Jakub Kicinski wrote:

> On Sat, 2 Jul 2022 15:23:57 +0800 (GMT+08:00) duoming@zju.edu.cn wrote:
> > > On Wed, 29 Jun 2022 18:49:41 +0800 Duoming Zhou wrote:  
> > > > When the link layer connection is broken, the rose->neighbour is
> > > > set to null. But rose->neighbour could be used by rose_connection()
> > > > and rose_release() later, because there is no synchronization among
> > > > them. As a result, the null-ptr-deref bugs will happen.
> > > > 
> > > > One of the null-ptr-deref bugs is shown below:
> > > > 
> > > >     (thread 1)                  |        (thread 2)
> > > >                                 |  rose_connect
> > > > rose_kill_by_neigh              |    lock_sock(sk)
> > > >   spin_lock_bh(&rose_list_lock) |    if (!rose->neighbour)
> > > >   rose->neighbour = NULL;//(1)  |
> > > >                                 |    rose->neighbour->use++;//(2)  
> > >   
> > > >  		if (rose->neighbour == neigh) {  
> > > 
> > > Why is it okay to perform this comparison without the socket lock,
> > > if we need a socket lock to clear it? Looks like rose_kill_by_neigh()
> > > is not guaranteed to clear all the uses of a neighbor.  
> > 
> > I am sorry, the comparision should also be protected with socket lock.
> > The rose_kill_by_neigh() only clear the neighbor that is passed as
> > parameter of rose_kill_by_neigh(). 
> 
> Don't think that's possible, you'd have to drop the neigh lock every
> time.

The neighbour is cleared in two situations.

(1) When the rose device is down, the rose_link_device_down() traverses
the rose_neigh_list and uses the rose_kill_by_neigh() to clear the
neighbors of the device.

void rose_link_device_down(struct net_device *dev)
{
	struct rose_neigh *rose_neigh;

	for (rose_neigh = rose_neigh_list; rose_neigh != NULL; rose_neigh = rose_neigh->next) {
		if (rose_neigh->dev == dev) {
			rose_del_route_by_neigh(rose_neigh);
			rose_kill_by_neigh(rose_neigh);
		}
	}
}

https://elixir.bootlin.com/linux/v5.19-rc4/source/net/rose/rose_route.c#L839

(2) When the level 2 link has timed out, the rose_link_failed() calls rose_kill_by_neigh()
to clear the rose_neigh.

https://elixir.bootlin.com/linux/v5.19-rc4/source/net/rose/rose_route.c#L813

> > > > +			sock_hold(s);
> > > > +			spin_unlock_bh(&rose_list_lock);
> > > > +			lock_sock(s);
> > > >  			rose_disconnect(s, ENETUNREACH, ROSE_OUT_OF_ORDER, 0);
> > > >  			rose->neighbour->use--;  
> > > 
> > > What protects the use counter?  
> > 
> > The use counter is protected by socket lock.
> 
> Which one, the neigh object can be shared by multiple sockets, no?

The sk_for_each() traverses the rose_list and uses the lock of the socket that is extracted
from the rose_list to protect the use counter.

diff --git a/net/rose/af_rose.c b/net/rose/af_rose.c
index bf2d986a6bc..6d5088b030a 100644
--- a/net/rose/af_rose.c
+++ b/net/rose/af_rose.c
@@ -165,14 +165,26 @@ void rose_kill_by_neigh(struct rose_neigh *neigh)
        struct sock *s;
 
        spin_lock_bh(&rose_list_lock);
+again:
        sk_for_each(s, &rose_list) {
                struct rose_sock *rose = rose_sk(s);
 
+               sock_hold(s);
+               spin_unlock_bh(&rose_list_lock);
+               lock_sock(s);
                if (rose->neighbour == neigh) {
                        rose_disconnect(s, ENETUNREACH, ROSE_OUT_OF_ORDER, 0);
                        rose->neighbour->use--;
                        rose->neighbour = NULL;
+                       release_sock(s);
+                       sock_put(s);
+                       spin_lock_bh(&rose_list_lock);
+                       goto again;
                }
+               release_sock(s);
+               sock_put(s);
+               spin_lock_bh(&rose_list_lock);
+               goto again;
        }
        spin_unlock_bh(&rose_list_lock);
 }

Best regards,
Duoming Zhou