[PATCH net 1/1] hv_netvsc: Fix a bug in netvsc_start_xmit()

[PATCH net 1/1] hv_netvsc: Fix a bug in netvsc_start_xmit()

[K. Y. Srinivasan]

Commit commit b08cc79155fc26d0d112b1470d1ece5034651a4b eliminated memory
allocation in the packet send path. This commit introduced a bug since it
did not account for the case if the skb was cloned. Fix this bug by
using the pre-reserved head room only if the skb is not cloned.

Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
---
 drivers/net/hyperv/netvsc_drv.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/drivers/net/hyperv/netvsc_drv.c b/drivers/net/hyperv/netvsc_drv.c
index a3a9d38..7eb0251 100644
--- a/drivers/net/hyperv/netvsc_drv.c
+++ b/drivers/net/hyperv/netvsc_drv.c
@@ -421,7 +421,7 @@ check_size:
 
 	pkt_sz = sizeof(struct hv_netvsc_packet) + RNDIS_AND_PPI_SIZE;
 
-	if (head_room < pkt_sz) {
+	if (skb->cloned ||  head_room < pkt_sz) {
 		packet = kmalloc(pkt_sz, GFP_ATOMIC);
 		if (!packet) {
 			/* out of memory, drop packet */
-- 
1.7.4.1

Re: [PATCH net 1/1] hv_netvsc: Fix a bug in netvsc_start_xmit()

[David Miller]

From: "K. Y. Srinivasan" <kys@microsoft.com>
Date: Mon, 27 Apr 2015 18:14:50 -0700

> Commit commit b08cc79155fc26d0d112b1470d1ece5034651a4b eliminated memory
> allocation in the packet send path. This commit introduced a bug since it
> did not account for the case if the skb was cloned. Fix this bug by
> using the pre-reserved head room only if the skb is not cloned.
> 
> Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>

We have generic infrastructure to do this, please try instead:

	err = skb_cow_head(skb, pkt_sz);

this will take care of everything for you and you can get rid
of all of this dynamic memory allocation etc. in this code
path.

RE: [PATCH net 1/1] hv_netvsc: Fix a bug in netvsc_start_xmit()

[KY Srinivasan]

> -----Original Message-----
> From: David Miller [mailto:davem@davemloft.net]
> Sent: Monday, April 27, 2015 7:57 PM
> To: KY Srinivasan
> Cc: netdev@vger.kernel.org; linux-kernel@vger.kernel.org;
> devel@linuxdriverproject.org; olaf@aepfle.de; apw@canonical.com;
> jasowang@redhat.com
> Subject: Re: [PATCH net 1/1] hv_netvsc: Fix a bug in netvsc_start_xmit()
> 
> From: "K. Y. Srinivasan" <kys@microsoft.com>
> Date: Mon, 27 Apr 2015 18:14:50 -0700
> 
> > Commit commit b08cc79155fc26d0d112b1470d1ece5034651a4b eliminated
> memory
> > allocation in the packet send path. This commit introduced a bug since it
> > did not account for the case if the skb was cloned. Fix this bug by
> > using the pre-reserved head room only if the skb is not cloned.
> >
> > Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
> 
> We have generic infrastructure to do this, please try instead:
> 
> 	err = skb_cow_head(skb, pkt_sz);
> 
> this will take care of everything for you and you can get rid
> of all of this dynamic memory allocation etc. in this code
> path.

Thanks David; I will resubmit this patch.

Regards,

K. Y

RE: [PATCH net 1/1] hv_netvsc: Fix a bug in netvsc_start_xmit()

[Dexuan Cui]

> -----Original Message-----
> From: devel [mailto:driverdev-devel-bounces@linuxdriverproject.org] On
> Behalf Of K. Y. Srinivasan
> Sent: Tuesday, April 28, 2015 9:15
> To: davem@davemloft.net; netdev@vger.kernel.org; linux-
> kernel@vger.kernel.org; devel@linuxdriverproject.org; olaf@aepfle.de;
> apw@canonical.com; jasowang@redhat.com
> Subject: [PATCH net 1/1] hv_netvsc: Fix a bug in netvsc_start_xmit()
> 
> Commit commit b08cc79155fc26d0d112b1470d1ece5034651a4b
> eliminated memory
> allocation in the packet send path. This commit introduced a bug since it
> did not account for the case if the skb was cloned. Fix this bug by
> using the pre-reserved head room only if the skb is not cloned.
> 
> Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
> ---
>  drivers/net/hyperv/netvsc_drv.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/drivers/net/hyperv/netvsc_drv.c
> b/drivers/net/hyperv/netvsc_drv.c
> index a3a9d38..7eb0251 100644
> --- a/drivers/net/hyperv/netvsc_drv.c
> +++ b/drivers/net/hyperv/netvsc_drv.c
> @@ -421,7 +421,7 @@ check_size:
> 
>  	pkt_sz = sizeof(struct hv_netvsc_packet) + RNDIS_AND_PPI_SIZE;
> 
> -	if (head_room < pkt_sz) {
> +	if (skb->cloned ||  head_room < pkt_sz) {
>  		packet = kmalloc(pkt_sz, GFP_ATOMIC);
>  		if (!packet) {
>  			/* out of memory, drop packet */
> --

Without the patch, the guest can panic due to memory corruption.

I confirm the patch can fix the panic I saw.

Tested-by: Dexuan Cui <decui@microsoft.com>

Thanks,
-- Dexuan

Re: [PATCH net 1/1] hv_netvsc: Fix a bug in netvsc_start_xmit()

[Sergei Shtylyov]

Hello.

On 04/28/2015 04:14 AM, K. Y. Srinivasan wrote:

> Commit commit b08cc79155fc26d0d112b1470d1ece5034651a4b eliminated memory

    One "commit" is enough. :-)
    And please also specify that commit's summary in parens.

> allocation in the packet send path. This commit introduced a bug since it
> did not account for the case if the skb was cloned. Fix this bug by
> using the pre-reserved head room only if the skb is not cloned.

> Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>

[...]

WBR, Sergei

RE: [PATCH net 1/1] hv_netvsc: Fix a bug in netvsc_start_xmit()

[KY Srinivasan]

> -----Original Message-----
> From: Sergei Shtylyov [mailto:sergei.shtylyov@cogentembedded.com]
> Sent: Tuesday, April 28, 2015 11:27 AM
> To: KY Srinivasan; davem@davemloft.net; netdev@vger.kernel.org; linux-
> kernel@vger.kernel.org; devel@linuxdriverproject.org; olaf@aepfle.de;
> apw@canonical.com; jasowang@redhat.com
> Subject: Re: [PATCH net 1/1] hv_netvsc: Fix a bug in netvsc_start_xmit()
> 
> Hello.
> 
> On 04/28/2015 04:14 AM, K. Y. Srinivasan wrote:
> 
> > Commit commit b08cc79155fc26d0d112b1470d1ece5034651a4b eliminated
> memory
> 
>     One "commit" is enough. :-)
>     And please also specify that commit's summary in parens.
> 
> > allocation in the packet send path. This commit introduced a bug since it
> > did not account for the case if the skb was cloned. Fix this bug by
> > using the pre-reserved head room only if the skb is not cloned.
> 
> > Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
> 
> [...]
> 
> WBR, Sergei

Will do; thanks.

K. Y