Linux Virtualization - Dec 2013 - [PATCH v2] virtio-net: free bufs correctly on invalid packet length

When a packet with invalid length arrives, ensure that the packet
is freed correctly if mergeable packet buffers and big packets
(GUEST_TSO4) are both enabled.

Signed-off-by: Michael Dalton <mwdalton at google.com>
---
 drivers/net/virtio_net.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 916241d..6a4665c 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -426,10 +426,10 @@ static void receive_buf(struct receive_queue *rq, void
*buf, unsigned int len)
 	if (unlikely(len < sizeof(struct virtio_net_hdr) + ETH_HLEN)) {
 		pr_debug("%s: short packet %i\n", dev->name, len);
 		dev->stats.rx_length_errors++;
-		if (vi->big_packets)
-			give_pages(rq, buf);
-		else if (vi->mergeable_rx_bufs)
+		if (vi->mergeable_rx_bufs)
 			put_page(virt_to_head_page(buf));
+		else if (vi->big_packets)
+			give_pages(rq, buf);
 		else
 			dev_kfree_skb(buf);
 		return;
-- 
1.8.5.1

Hi,

A quick note on this patch: I have confirmed that without this
patch a kernel crash occurs if we force a 'packet too short' error
sufficiently many times. This patch eliminates the kernel crash.

Since this crash would be triggered by a hypervisor bug, I made a
small change not reflected in the above patch to make the crash easier
to reproduce for testing purposes. I treated 1 out of every 128 packets
with len < MERGE_BUFFER_LEN as 'too short'. With this change in
place, just running netperf will cause the sender to crash very quickly
(the receiver will transmit pure data ACKs that meet the drop criteria).

If anyone would like to reproduce the crash using the above setup,
I added an unsigned int num_packets field to struct receive_queue and
changed the if condition for the packet too short check in receive_buf()
from:
        if (unlikely(len < sizeof(struct virtio_net_hdr) + ETH_HLEN)) {
to:
        if (unlikely((len < sizeof(struct virtio_net_hdr) + ETH_HLEN) ||
                     (len < MERGE_BUFFER_LEN &&
                      ((++rq->num_packets & 127) == 0)))) {

Best,

Mike

On 12/06/2013 05:14 AM, Michael Dalton wrote:
> When a packet with invalid length arrives, ensure that the packet
> is freed correctly if mergeable packet buffers and big packets
> (GUEST_TSO4) are both enabled.
>
> Signed-off-by: Michael Dalton <mwdalton at google.com>
> ---
>  drivers/net/virtio_net.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 916241d..6a4665c 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -426,10 +426,10 @@ static void receive_buf(struct receive_queue *rq,
void *buf, unsigned int len)
>  	if (unlikely(len < sizeof(struct virtio_net_hdr) + ETH_HLEN)) {
>  		pr_debug("%s: short packet %i\n", dev->name, len);
>  		dev->stats.rx_length_errors++;
> -		if (vi->big_packets)
> -			give_pages(rq, buf);
> -		else if (vi->mergeable_rx_bufs)
> +		if (vi->mergeable_rx_bufs)
>  			put_page(virt_to_head_page(buf));
> +		else if (vi->big_packets)
> +			give_pages(rq, buf);
>  		else
>  			dev_kfree_skb(buf);
>  		return;
Acked-by: Jason Wang <jasowang at redhat.com>

On Thu, Dec 05, 2013 at 01:14:05PM -0800, Michael Dalton
wrote:
> When a packet with invalid length arrives, ensure that the packet
> is freed correctly if mergeable packet buffers and big packets
> (GUEST_TSO4) are both enabled.
> 
> Signed-off-by: Michael Dalton <mwdalton at google.com>
Acked-by: Andrew Vagin <avagin at openvz.org>
> ---
>  drivers/net/virtio_net.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 916241d..6a4665c 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -426,10 +426,10 @@ static void receive_buf(struct receive_queue *rq,
void *buf, unsigned int len)
>  	if (unlikely(len < sizeof(struct virtio_net_hdr) + ETH_HLEN)) {
>  		pr_debug("%s: short packet %i\n", dev->name, len);
>  		dev->stats.rx_length_errors++;
> -		if (vi->big_packets)
> -			give_pages(rq, buf);
> -		else if (vi->mergeable_rx_bufs)
> +		if (vi->mergeable_rx_bufs)
>  			put_page(virt_to_head_page(buf));
> +		else if (vi->big_packets)
> +			give_pages(rq, buf);
>  		else
>  			dev_kfree_skb(buf);
>  		return;
> -- 
> 1.8.5.1
>

From: Michael Dalton <mwdalton at google.com>
Date: Thu,  5 Dec 2013 13:14:05 -0800
> When a packet with invalid length arrives, ensure that the packet
> is freed correctly if mergeable packet buffers and big packets
> (GUEST_TSO4) are both enabled.
> 
> Signed-off-by: Michael Dalton <mwdalton at google.com>
Applied, is this needed for -stable?

Hi David,

This patch fixes a bug introduced by 2613af0ed18a ("virtio_net:
migrate mergeable rx buffers to page frag allocators"). The bug
is present in both net-next and net. Thanks

Best,

Mike

On Fri, Dec 6, 2013 at 1:32 PM, David Miller <davem at davemloft.net>
wrote:
> From: Michael Dalton <mwdalton at google.com>
> Date: Thu,  5 Dec 2013 13:14:05 -0800
>
>> When a packet with invalid length arrives, ensure that the packet
>> is freed correctly if mergeable packet buffers and big packets
>> (GUEST_TSO4) are both enabled.
>>
>> Signed-off-by: Michael Dalton <mwdalton at google.com>
>
> Applied, is this needed for -stable?

Michael Dalton <mwdalton at google.com> writes:
> When a packet with invalid length arrives, ensure that the packet
> is freed correctly if mergeable packet buffers and big packets
> (GUEST_TSO4) are both enabled.
>
> Signed-off-by: Michael Dalton <mwdalton at google.com>
Acked-by: Rusty Russell <rusty at rustcorp.com.au>

Thanks!
> ---
>  drivers/net/virtio_net.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 916241d..6a4665c 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -426,10 +426,10 @@ static void receive_buf(struct receive_queue *rq,
void *buf, unsigned int len)
>  	if (unlikely(len < sizeof(struct virtio_net_hdr) + ETH_HLEN)) {
>  		pr_debug("%s: short packet %i\n", dev->name, len);
>  		dev->stats.rx_length_errors++;
> -		if (vi->big_packets)
> -			give_pages(rq, buf);
> -		else if (vi->mergeable_rx_bufs)
> +		if (vi->mergeable_rx_bufs)
>  			put_page(virt_to_head_page(buf));
> +		else if (vi->big_packets)
> +			give_pages(rq, buf);
>  		else
>  			dev_kfree_skb(buf);
>  		return;
> -- 
> 1.8.5.1