[PATCH 6.1.y] virtio_net: Do not send RSS key if it is not supported

[Konstantin Ovsepian]

From: Breno Leitao <leitao@debian.org>

commit 059a49aa2e25c58f90b50151f109dd3c4cdb3a47 upstream

There is a bug when setting the RSS options in virtio_net that can break
the whole machine, getting the kernel into an infinite loop.

Running the following command in any QEMU virtual machine with virtionet
will reproduce this problem:

    # ethtool -X eth0  hfunc toeplitz

This is how the problem happens:

1) ethtool_set_rxfh() calls virtnet_set_rxfh()

2) virtnet_set_rxfh() calls virtnet_commit_rss_command()

3) virtnet_commit_rss_command() populates 4 entries for the rss
scatter-gather

4) Since the command above does not have a key, then the last
scatter-gatter entry will be zeroed, since rss_key_size == 0.
sg_buf_size = vi->rss_key_size;

5) This buffer is passed to qemu, but qemu is not happy with a buffer
with zero length, and do the following in virtqueue_map_desc() (QEMU
function):

  if (!sz) {
      virtio_error(vdev, "virtio: zero sized buffers are not allowed");

6) virtio_error() (also QEMU function) set the device as broken

    vdev->broken = true;

7) Qemu bails out, and do not repond this crazy kernel.

8) The kernel is waiting for the response to come back (function
virtnet_send_command())

9) The kernel is waiting doing the following :

      while (!virtqueue_get_buf(vi->cvq, &tmp) &&
             !virtqueue_is_broken(vi->cvq))
              cpu_relax();

10) None of the following functions above is true, thus, the kernel
loops here forever. Keeping in mind that virtqueue_is_broken() does
not look at the qemu `vdev->broken`, so, it never realizes that the
vitio is broken at QEMU side.

Fix it by not sending RSS commands if the feature is not available in
the device.

Fixes: c7114b1249fa ("drivers/net/virtio_net: Added basic RSS support.")
Cc: stable@vger.kernel.org
Cc: qemu-devel@nongnu.org
Signed-off-by: Breno Leitao <leitao@debian.org>
Reviewed-by: Heng Qi <hengqi@linux.alibaba.com>
Reviewed-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
(cherry picked from commit 059a49aa2e25c58f90b50151f109dd3c4cdb3a47)
Signed-off-by: Konstantin Ovsepian <ovs@ovs.to>
---
 drivers/net/virtio_net.c | 26 ++++++++++++++++++++++----
 1 file changed, 22 insertions(+), 4 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 45f1a871b7da..32cddb633793 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -2948,19 +2948,35 @@ static int virtnet_get_rxfh(struct net_device *dev, u32 
*indir, u8 *key, u8 *hfu
 static int virtnet_set_rxfh(struct net_device *dev, const u32 *indir, const u8 
*key, const u8 hfunc)
 {
        struct virtnet_info *vi = netdev_priv(dev);
+       bool update = false;
        int i;
 
        if (hfunc != ETH_RSS_HASH_NO_CHANGE && hfunc != ETH_RSS_HASH_TOP)
                return -EOPNOTSUPP;
 
        if (indir) {
+               if (!vi->has_rss)
+                       return -EOPNOTSUPP;
+
                for (i = 0; i < vi->rss_indir_table_size; ++i)
                        vi->ctrl->rss.indirection_table[i] = indir[i];
+               update = true;
        }
-       if (key)
+
+       if (key) {
+               /* If either _F_HASH_REPORT or _F_RSS are negotiated, the
+                * device provides hash calculation capabilities, that is,
+                * hash_key is configured.
+                */
+               if (!vi->has_rss && !vi->has_rss_hash_report)
+                       return -EOPNOTSUPP;
+
                memcpy(vi->ctrl->rss.key, key, vi->rss_key_size);
+               update = true;
+       }
 
-       virtnet_commit_rss_command(vi);
+       if (update)
+               virtnet_commit_rss_command(vi);
 
        return 0;
 }
@@ -3852,13 +3868,15 @@ static int virtnet_probe(struct virtio_device *vdev)
        if (virtio_has_feature(vdev, VIRTIO_NET_F_HASH_REPORT))
                vi->has_rss_hash_report = true;
 
-       if (virtio_has_feature(vdev, VIRTIO_NET_F_RSS))
+       if (virtio_has_feature(vdev, VIRTIO_NET_F_RSS)) {
                vi->has_rss = true;
 
-       if (vi->has_rss || vi->has_rss_hash_report) {
                vi->rss_indir_table_size =
                        virtio_cread16(vdev, offsetof(struct virtio_net_config,
                                rss_max_indirection_table_length));
+       }
+
+       if (vi->has_rss || vi->has_rss_hash_report) {
                vi->rss_key_size =
                        virtio_cread8(vdev, offsetof(struct virtio_net_config, 
rss_max_key_size));
 
-- 
2.43.0