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

[Greg KH]

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