Re: [PATCH 4.14] Fix double fget() in vhost_net_set_backend()

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On Wed, Jun 07, 2023 at 08:35:29PM +0200, Greg Kroah-Hartman wrote:
> CAUTION: This email originated from outside of the organization. Do not click links or open attachments unless you can confirm the sender and know the content is safe.
> 
> 
> 
> On Tue, Jun 06, 2023 at 11:28:31AM -0700, Samuel Mendoza-Jonas wrote:
> > From: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
> >
> > commit fb4554c2232e44d595920f4d5c66cf8f7d13f9bc upstream.
> >
> > Descriptor table is a shared resource; two fget() on the same descriptor
> > may return different struct file references.  get_tap_ptr_ring() is
> > called after we'd found (and pinned) the socket we'll be using and it
> > tries to find the private tun/tap data structures associated with it.
> > Redoing the lookup by the same file descriptor we'd used to get the
> > socket is racy - we need to same struct file.
> >
> > Thanks to Jason for spotting a braino in the original variant of patch -
> > I'd missed the use of fd == -1 for disabling backend, and in that case
> > we can end up with sock == NULL and sock != oldsock.
> >
> > Cc: stable@xxxxxxxxxx
> > Acked-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
> > Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
> > Signed-off-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
> > Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> 
> I did not sign off on this patch, where did that come from?
> 
> Please be more careful.
> 
> thanks,
> 
> greg k-h

Ah my apologies, that must have come from the commit to the other stable
branches.

Thanks,
Sam



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