Re: [PATCH] vhost: It's better to use size_t for the 3rd parameter of vhost_exceeds_weight()

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On 2019/9/23 下午5:12, wangxu (AE) wrote:
Hi Michael

	Thanks for your fast reply.

	As the following code, the 2nd branch of iov_iter_advance() does not check if i->count < size, when this happens, i->count -= size may cause len exceed INT_MAX, and then total_len exceed INT_MAX.

	handle_tx_copy() ->
		get_tx_bufs(..., &len, ...) ->
			init_iov_iter() ->
				iov_iter_advance(iter, ...) 	// has 3 branches:
					pipe_advance() 	 	// has checked the size: if (unlikely(i->count < size)) size = i->count;
					iov_iter_is_discard() ... 	// no check.


Yes, but I don't think we use ITER_DISCARD.

Thanks


					iterate_and_advance() 	//has checked: if (unlikely(i->count < n)) n = i->count;
				return iov_iter_count(iter);

-----Original Message-----
From: Michael S. Tsirkin [mailto:mst@xxxxxxxxxx]
Sent: Monday, September 23, 2019 4:07 PM
To: wangxu (AE) <wangxu72@xxxxxxxxxx>
Cc: jasowang@xxxxxxxxxx; kvm@xxxxxxxxxxxxxxx; virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx; netdev@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
Subject: Re: [PATCH] vhost: It's better to use size_t for the 3rd parameter of vhost_exceeds_weight()

On Mon, Sep 23, 2019 at 03:46:41PM +0800, wangxu wrote:
From: Wang Xu <wangxu72@xxxxxxxxxx>

Caller of vhost_exceeds_weight(..., total_len) in drivers/vhost/net.c
usually pass size_t total_len, which may be affected by rx/tx package.

Signed-off-by: Wang Xu <wangxu72@xxxxxxxxxx>

Puts a bit more pressure on the register file ...
why do we care? Is there some way that it can exceed INT_MAX?

---
  drivers/vhost/vhost.c | 4 ++--
  drivers/vhost/vhost.h | 7 ++++---
  2 files changed, 6 insertions(+), 5 deletions(-)

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c index
36ca2cf..159223a 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -412,7 +412,7 @@ static void vhost_dev_free_iovecs(struct vhost_dev
*dev)  }
bool vhost_exceeds_weight(struct vhost_virtqueue *vq,
-			  int pkts, int total_len)
+			  int pkts, size_t total_len)
  {
  	struct vhost_dev *dev = vq->dev;
@@ -454,7 +454,7 @@ static size_t vhost_get_desc_size(struct
vhost_virtqueue *vq,
void vhost_dev_init(struct vhost_dev *dev,
  		    struct vhost_virtqueue **vqs, int nvqs,
-		    int iov_limit, int weight, int byte_weight)
+		    int iov_limit, int weight, size_t byte_weight)
  {
  	struct vhost_virtqueue *vq;
  	int i;
diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h index
e9ed272..8d80389d 100644
--- a/drivers/vhost/vhost.h
+++ b/drivers/vhost/vhost.h
@@ -172,12 +172,13 @@ struct vhost_dev {
  	wait_queue_head_t wait;
  	int iov_limit;
  	int weight;
-	int byte_weight;
+	size_t byte_weight;
  };

This just costs extra memory, and value is never large, so I don't think this matters.

-bool vhost_exceeds_weight(struct vhost_virtqueue *vq, int pkts, int
total_len);
+bool vhost_exceeds_weight(struct vhost_virtqueue *vq, int pkts,
+			  size_t total_len);
  void vhost_dev_init(struct vhost_dev *, struct vhost_virtqueue **vqs,
-		    int nvqs, int iov_limit, int weight, int byte_weight);
+		    int nvqs, int iov_limit, int weight, size_t byte_weight);
  long vhost_dev_set_owner(struct vhost_dev *dev);  bool
vhost_dev_has_owner(struct vhost_dev *dev);  long
vhost_dev_check_owner(struct vhost_dev *);
--
1.8.5.6



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