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Date: Mon, 8 Oct 2018 10:20:24 +0800 From: Jason Wang <jasowang@...hat.com> To: "Michael S. Tsirkin" <mst@...hat.com> Cc: stefanha@...hat.com, kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org, linux-kernel@...r.kernel.org, sergei.shtylyov@...entembedded.com Subject: Re: [PATCH net V2] vhost-vsock: fix use after free On 2018年09月28日 07:50, Michael S. Tsirkin wrote: > On Fri, Sep 28, 2018 at 07:37:37AM +0800, Jason Wang wrote: >> >> On 2018年09月28日 01:04, Michael S. Tsirkin wrote: >>> On Thu, Sep 27, 2018 at 08:22:04PM +0800, Jason Wang wrote: >>>> The access of vsock is not protected by vhost_vsock_lock. This may >>>> lead to use after free since vhost_vsock_dev_release() may free the >>>> pointer at the same time. >>>> >>>> Fix this by holding the lock during the access. >>>> >>>> Reported-by:syzbot+e3e074963495f92a89ed@...kaller.appspotmail.com >>>> Fixes: 16320f363ae1 ("vhost-vsock: add pkt cancel capability") >>>> Fixes: 433fc58e6bf2 ("VSOCK: Introduce vhost_vsock.ko") >>>> Cc: Stefan Hajnoczi<stefanha@...hat.com> >>>> Signed-off-by: Jason Wang<jasowang@...hat.com> >>> Wow is that really the best we can do? >> For net/stable, probably yes. >> >>> A global lock on a data path >>> operation? >> It's already there, > &vhost_vsock_lock? were is it takes on data path? Ok, but the current code use list which means a global lock is needed anyway here. > >> and the patch only increase the critical section. >> >>> Granted use after free is nasty but Stefan said he sees >>> a way to fix it using a per socket refcount. He's on vacation >>> until Oct 4 though ... >>> >> Stefan has acked the pacth, so I think it's ok? We can do optimization for >> -next on top. >> >> Thanks > > Well on high SMP serializing can drop performance as much as x100 so I'm > not sure it's appropriate - seems to fix a bug but can introduce a > regression. Let's see how does a proper fix look first? > It looks to me hlist + RCU is better. But I'm not sure it's suitable for -net/-stable. Thanks
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