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SubjectRe: [PATCH] vhost/vsock: fix vhost vsock cid hashing inconsistent
From: Zha Bin <>
Date: Tue, 8 Jan 2019 16:07:03 +0800

> 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:
> Signed-off-by: Zha Bin <>
> Reviewed-by: Liu Jiang <>

Applied, thank you.

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