Re: Re: [PATCH v3] virtio-net: Add validation for used length

On Mon, May 31, 2021 at 3:51 PM Jason Wang [off-list ref] wrote:

在 2021/5/31 下午3:19, Yongji Xie 写道:

quoted

On Mon, May 31, 2021 at 2:49 PM Jason Wang [off-list ref] wrote:

quoted

在 2021/5/28 下午8:11, Xie Yongji 写道:

quoted

This adds validation for used length (might come
from an untrusted device) to avoid data corruption
or loss.

Signed-off-by: Xie Yongji <redacted>
---
   drivers/net/virtio_net.c | 28 +++++++++++++++++++++-------
   1 file changed, 21 insertions(+), 7 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 073fec4c0df1..01f15b65824c 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c

@@ -732,6 +732,17 @@ static struct sk_buff *receive_small(struct net_device *dev,

       rcu_read_lock();
       xdp_prog = rcu_dereference(rq->xdp_prog);
+     if (unlikely(len > GOOD_PACKET_LEN)) {
+             pr_debug("%s: rx error: len %u exceeds max size %d\n",
+                      dev->name, len, GOOD_PACKET_LEN);
+             dev->stats.rx_length_errors++;
+             if (xdp_prog)
+                     goto err_xdp;
+
+             rcu_read_unlock();
+             put_page(page);
+             return NULL;
+     }
       if (xdp_prog) {
               struct virtio_net_hdr_mrg_rxbuf *hdr = buf + header_offset;
               struct xdp_frame *xdpf;

@@ -888,6 +899,16 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,

       rcu_read_lock();
       xdp_prog = rcu_dereference(rq->xdp_prog);
+     if (unlikely(len > truesize)) {
+             pr_debug("%s: rx error: len %u exceeds truesize %lu\n",
+                      dev->name, len, (unsigned long)ctx);
+             dev->stats.rx_length_errors++;
+             if (xdp_prog)
+                     goto err_xdp;
+
+             rcu_read_unlock();
+             goto err_skb;
+     }

Patch looks correct but I'd rather not bother XDP here. It would be
better if we just do the check before rcu_read_lock() and use err_skb
directly() to avoid RCU/XDP stuffs.

If so, we will miss the statistics of xdp_drops. Is it OK?

It should be ok, we still had drops and it was dropped before dealing
with XDP.

The motivation is to have simple codes.

OK, will send v4 soon.

Thanks,
Yongji