linux-kernel - Re: [PATCH] vhost/vsock: fix vhost vsock cid hashing inconsistent

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Date:   Tue, 8 Jan 2019 11:24:11 +0000
From:   Stefan Hajnoczi <stefanha@...il.com>
To:     Zha Bin <zhabin@...ux.alibaba.com>
Cc:     stefanha@...hat.com, mst@...hat.com, jasowang@...hat.com,
        kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        gerry@...ux.alibaba.com, kata-dev@...ts.katacontainers.io
Subject: Re: [PATCH] vhost/vsock: fix vhost vsock cid hashing inconsistent

On Tue, Jan 08, 2019 at 04:07:03PM +0800, Zha Bin wrote:
> 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@...ux.alibaba.com>
> Reviewed-by: Liu Jiang <gerry@...ux.alibaba.com>
> ---
>  drivers/vhost/vsock.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

Thanks for tracking this down!

Reviewed-by: Stefan Hajnoczi <stefanha@...hat.com>

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