[SRU B/C/D] vhost/vsock: fix vhost vsock cid hashing inconsistent

[Seth Forshee]

On Wed, Jan 30, 2019 at 02:45:50PM +0100, 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>

Acked-by: Seth Forshee <seth.forshee at canonical.com>

Applied to disco/master-next, thanks!