APPLIED(B,C): [SRU B/C/D] vhost/vsock: fix vhost vsock cid hashing inconsistent

[Khaled Elmously]

On 2019-02-04 00:22:25 , Khaled Elmously wrote:
> On 2019-01-30 14:45:50 , Stefan Bader wrote:
> > From: Zha Bin <zhabin at linux.alibaba.com>
> > 
> > BugLink: https://bugs.launchpad.net/bugs/1813934
> > 
> > The vsock core only supports 32bit CID, but the Virtio-vsock spec define
> > CID (dst_cid and src_cid) as u64 and the upper 32bits is reserved as
> > zero. This inconsistency causes one bug in vhost vsock driver. The
> > scenarios is:
> > 
> >   0. A hash table (vhost_vsock_hash) is used to map an CID to a vsock
> >   object. And hash_min() is used to compute the hash key. hash_min() is
> >   defined as:
> >   (sizeof(val) <= 4 ? hash_32(val, bits) : hash_long(val, bits)).
> >   That means the hash algorithm has dependency on the size of macro
> >   argument 'val'.
> >   0. In function vhost_vsock_set_cid(), a 64bit CID is passed to
> >   hash_min() to compute the hash key when inserting a vsock object into
> >   the hash table.
> >   0. In function vhost_vsock_get(), a 32bit CID is passed to hash_min()
> >   to compute the hash key when looking up a vsock for an CID.
> > 
> > Because the different size of the CID, hash_min() returns different hash
> > key, thus fails to look up the vsock object for an CID.
> > 
> > To fix this bug, we keep CID as u64 in the IOCTLs and virtio message
> > headers, but explicitly convert u64 to u32 when deal with the hash table
> > and vsock core.
> > 
> > Fixes: 834e772c8db0 ("vhost/vsock: fix use-after-free in network stack callers")
> > Link: https://github.com/stefanha/virtio/blob/vsock/trunk/content.tex
> > Signed-off-by: Zha Bin <zhabin at linux.alibaba.com>
> > Reviewed-by: Liu Jiang <gerry at linux.alibaba.com>
> > Reviewed-by: Stefan Hajnoczi <stefanha at redhat.com>
> > Acked-by: Jason Wang <jasowang at redhat.com>
> > Signed-off-by: David S. Miller <davem at davemloft.net>
> > 
> > (backported from commit 7fbe078c37aba3088359c9256c1a1d0c3e39ee81)
> > [minor context adjustment]
> > Signed-off-by: Stefan Bader <stefan.bader at canonical.com>
> > ---
> > 
> > The same backport applied to all trees. Since it is in v5.0-rc3, it will
> > not be needed for unstable.
> > 
> > -Stefan
> > 
> >  drivers/vhost/vsock.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
> > index c6f550155f53..fe1dd9cd5d4e 100644
> > --- a/drivers/vhost/vsock.c
> > +++ b/drivers/vhost/vsock.c
> > @@ -634,7 +634,7 @@ static int vhost_vsock_set_cid(struct vhost_vsock *vsock, u64 guest_cid)
> >  		hash_del_rcu(&vsock->hash);
> >  
> >  	vsock->guest_cid = guest_cid;
> > -	hash_add_rcu(vhost_vsock_hash, &vsock->hash, guest_cid);
> > +	hash_add_rcu(vhost_vsock_hash, &vsock->hash, vsock->guest_cid);
> >  	spin_unlock_bh(&vhost_vsock_lock);
> >  
> >  	return 0;
> 
> Acked-by: Khalid Elmously <khalid.elmously at canonical.com>
>