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

On Wed, Apr 24, 2024 at 03:57:04AM -0700, Konstantin Ovsepian wrote:
> 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(-)

Now queued up,t hanks.

greg k-h