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

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Message-ID: <ebcc2c6c-d188-fe0f-2d24-0997203484f7@redhat.com>
Date:   Fri, 11 Jan 2019 12:13:36 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Zha Bin <zhabin@...ux.alibaba.com>, stefanha@...hat.com
Cc:     mst@...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 2019/1/8 下午4:07, 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(-)
>
> diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
> index bc42d38ae031..3fbc068eaa9b 100644
> --- a/drivers/vhost/vsock.c
> +++ b/drivers/vhost/vsock.c
> @@ -642,7 +642,7 @@ 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);
>   	mutex_unlock(&vhost_vsock_mutex);
>   
>   	return 0;


Acked-by: Jason Wang <jasowang@...hat.com>