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

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