Re: [PATCH net v3 2/2] net: rose: fix null-ptr-deref caused by rose_kill_by_neigh

[Paolo Abeni]

On Fri, 2022-06-24 at 09:05 +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)
> 
> 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@xxxxxxxxxx>
> ---
> Changes since v2:
>   - v2: Fix refcount leak of sock.
> 
>  net/rose/af_rose.c    | 6 ++++++
>  net/rose/rose_route.c | 2 ++
>  2 files changed, 8 insertions(+)
> 
> diff --git a/net/rose/af_rose.c b/net/rose/af_rose.c
> index bf2d986a6bc..5caa222c490 100644
> --- a/net/rose/af_rose.c
> +++ b/net/rose/af_rose.c
> @@ -169,9 +169,15 @@ void rose_kill_by_neigh(struct rose_neigh *neigh)
>  		struct rose_sock *rose = rose_sk(s);
>  
>  		if (rose->neighbour == neigh) {
> +			sock_hold(s);
>  			rose_disconnect(s, ENETUNREACH, ROSE_OUT_OF_ORDER, 0);
>  			rose->neighbour->use--;
> +			spin_unlock_bh(&rose_list_lock);
> +			lock_sock(s);
>  			rose->neighbour = NULL;
> +			release_sock(s);
> +			spin_lock_bh(&rose_list_lock);

I'm sorry, I likely was not clear enough in my previous reply. This is
broken. If a list is [spin_]lock protected, you can't release the lock,
reacquire it and continue traversing the list from the [now invalid]
same iterator.

e.g. if s is removed from the list, even if the sock is not de-
allocated due to the addtional refcount, the traversing will errnously
stop after this sock, instead of continuing processing the remaining
socks in the list.

A possible alternative, not even build-tested would be:
---
diff --git a/include/net/rose.h b/include/net/rose.h
index 0f0a4ce0fee7..090db11d528f 100644
--- a/include/net/rose.h
+++ b/include/net/rose.h
@@ -145,6 +145,7 @@ struct rose_sock {
 	struct rose_facilities_struct facilities;
 	struct timer_list	timer;
 	struct timer_list	idletimer;
+	struct rose_sock	*dl_next;
 };
 
 #define rose_sk(sk) ((struct rose_sock *)(sk))
diff --git a/net/rose/af_rose.c b/net/rose/af_rose.c
index 5caa222c490e..01f3c50f0921 100644
--- a/net/rose/af_rose.c
+++ b/net/rose/af_rose.c
@@ -162,25 +162,32 @@ static void rose_remove_socket(struct sock *sk)
  */
 void rose_kill_by_neigh(struct rose_neigh *neigh)
 {
-	struct sock *s;
+	struct rose_sock *del_list = NULL;
+	struct sock *s, *tmp;
 
 	spin_lock_bh(&rose_list_lock);
-	sk_for_each(s, &rose_list) {
+	sk_for_each_safe(s, tmp, &rose_list) {
 		struct rose_sock *rose = rose_sk(s);
 
 		if (rose->neighbour == neigh) {
-			sock_hold(s);
-			rose_disconnect(s, ENETUNREACH, ROSE_OUT_OF_ORDER, 0);
-			rose->neighbour->use--;
-			spin_unlock_bh(&rose_list_lock);
-			lock_sock(s);
-			rose->neighbour = NULL;
-			release_sock(s);
-			spin_lock_bh(&rose_list_lock);
-			sock_put(s);
+			__sk_del_node(s);
+			s->dl_next = del_list;
+			del_list = s;
 		}
 	}
 	spin_unlock_bh(&rose_list_lock);
+
+	while (del_list) {
+		s = del_list;
+		del_list = s->dl_next;
+
+		lock_sock(s);
+		rose_disconnect(s, ENETUNREACH, ROSE_OUT_OF_ORDER, 0);
+		rose->neighbour->use--;
+		rose->neighbour = NULL;
+		release_sock(s);
+		sock_put(s);
+	}
 }
 
 /*
---

Paolo