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

[Stefan Bader]

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;
-- 
2.17.1