Messages in this thread | | | Date | Sat, 2 Jul 2022 15:23:57 +0800 (GMT+08:00) | From | duoming@zju ... | Subject | Re: [PATCH v4] net: rose: fix null-ptr-deref caused by rose_kill_by_neigh |
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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
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