linux-kernel - Re: [PATCH v3 09/13] vhost/vdpa: remove vhost_vdpa_config

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Date:   Fri, 5 Feb 2021 10:16:51 +0100
From:   Stefano Garzarella <sgarzare@...hat.com>
To:     Jason Wang <jasowang@...hat.com>,
        "Michael S. Tsirkin" <mst@...hat.com>
Cc:     virtualization@...ts.linux-foundation.org,
        Xie Yongji <xieyongji@...edance.com>, kvm@...r.kernel.org,
        Laurent Vivier <lvivier@...hat.com>,
        Stefan Hajnoczi <stefanha@...hat.com>,
        Max Gurtovoy <mgurtovoy@...dia.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 09/13] vhost/vdpa: remove vhost_vdpa_config_validate()

On Fri, Feb 05, 2021 at 11:27:32AM +0800, Jason Wang wrote:
>
>On 2021/2/5 上午1:22, Stefano Garzarella wrote:
>>get_config() and set_config() callbacks in the 'struct vdpa_config_ops'
>>usually already validated the inputs. Also now they can return an error,
>>so we don't need to validate them here anymore.
>>
>>Let's use the return value of these callbacks and return it in case of
>>error in vhost_vdpa_get_config() and vhost_vdpa_set_config().
>>
>>Originally-by: Xie Yongji <xieyongji@...edance.com>
>>Signed-off-by: Stefano Garzarella <sgarzare@...hat.com>
>>---
>>  drivers/vhost/vdpa.c | 41 +++++++++++++----------------------------
>>  1 file changed, 13 insertions(+), 28 deletions(-)
>>
>>diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
>>index ef688c8c0e0e..d61e779000a8 100644
>>--- a/drivers/vhost/vdpa.c
>>+++ b/drivers/vhost/vdpa.c
>>@@ -185,51 +185,35 @@ static long vhost_vdpa_set_status(struct vhost_vdpa *v, u8 __user *statusp)
>>  	return 0;
>>  }
>>-static int vhost_vdpa_config_validate(struct vhost_vdpa *v,
>>-				      struct vhost_vdpa_config *c)
>>-{
>>-	long size = 0;
>>-
>>-	switch (v->virtio_id) {
>>-	case VIRTIO_ID_NET:
>>-		size = sizeof(struct virtio_net_config);
>>-		break;
>>-	}
>>-
>>-	if (c->len == 0)
>>-		return -EINVAL;
>>-
>>-	if (c->len > size - c->off)
>>-		return -E2BIG;
>>-
>>-	return 0;
>>-}
>>-
>>  static long vhost_vdpa_get_config(struct vhost_vdpa *v,
>>  				  struct vhost_vdpa_config __user *c)
>>  {
>>  	struct vdpa_device *vdpa = v->vdpa;
>>  	struct vhost_vdpa_config config;
>>  	unsigned long size = offsetof(struct vhost_vdpa_config, buf);
>>+	long ret;
>>  	u8 *buf;
>>  	if (copy_from_user(&config, c, size))
>>  		return -EFAULT;
>>-	if (vhost_vdpa_config_validate(v, &config))
>>+	if (config.len == 0)
>>  		return -EINVAL;
>>  	buf = kvzalloc(config.len, GFP_KERNEL);
>
>
>Then it means usersapce can allocate a very large memory.

Good point.

>
>Rethink about this, we should limit the size here (e.g PAGE_SIZE) or 
>fetch the config size first (either through a config ops as you 
>suggested or a variable in the vdpa device that is initialized during 
>device creation).

Maybe PAGE_SIZE is okay as a limit.

If instead we want to fetch the config size, then better a config ops in 
my opinion, to avoid adding a new parameter to __vdpa_alloc_device().

I vote for PAGE_SIZE, but it isn't a strong opinion.

What do you and @Michael suggest?

Thanks,
Stefano