linux-kernel - Re: KASAN: use-after-free Read in rdma

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Date:   Tue, 18 Feb 2020 15:13:51 -0400
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Hillf Danton <hdanton@...a.com>
Cc:     syzbot <syzbot+adb15cf8c2798e4e0db4@...kaller.appspotmail.com>,
        chuck.lever@...cle.com, danielj@...lanox.com, danitg@...lanox.com,
        dledford@...hat.com, leon@...nel.org, linux-kernel@...r.kernel.org,
        linux-rdma@...r.kernel.org, parav@...lanox.com,
        swise@...ngridcomputing.com, syzkaller-bugs@...glegroups.com
Subject: Re: KASAN: use-after-free Read in rdma_listen (2)

On Tue, Feb 18, 2020 at 08:27:17PM +0800, Hillf Danton wrote:
> Check if rdma is being reclaimed before listening on device while
> reclaimer is waiting for rdma to become quiesce.

This is the usual syzkaller bug in rdma_cm

The test causes rdma_resolve_addr() and rdma_listen() to run
concurrently.

There is no sane locking, so in turn this causes invariants to become
violated, in particular, in rdma_listen() we can have !id->device
but also !cma_any_addr(cma_src_addr(id_priv).

This causes cma_listen_on_all() to wrongly be called and because the
invariant is screwed up cma_cancel_listens() doesn't undo it.

Thus we fail to list_del id_priv->list from the listen_any_list and
the next manipulation of the list gets a use-after on the list member
which was now freed.

The fix is the same as all the others, add some kind of locking
instead of all this defective cma_comp_exch() thing..

Jason