Re: [PATCH v4] net: rose: fix null-ptr-deref caused by rose_kill_by_neigh
From: Jakub Kicinski <kuba@kernel.org>
Date: 2022-07-02 02:42:06
Also in:
linux-hams, lkml
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.
quoted hunk ↗ jump to hunk
+ 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); }