diff mbox series

[bpf-next,V5,4/5] bpf: drop MTU check when doing TC-BPF redirect to ingress

Message ID 160407666748.1525159.1515139110258948831.stgit@firesoul (mailing list archive)
State Changes Requested
Delegated to: BPF
Headers show
Series Subj: bpf: New approach for BPF MTU handling | expand

Commit Message

Jesper Dangaard Brouer Oct. 30, 2020, 4:51 p.m. UTC
The use-case for dropping the MTU check when TC-BPF does redirect to
ingress, is described by Eyal Birger in email[0]. The summary is the
ability to increase packet size (e.g. with IPv6 headers for NAT64) and
ingress redirect packet and let normal netstack fragment packet as needed.

[0] https://lore.kernel.org/netdev/CAHsH6Gug-hsLGHQ6N0wtixdOa85LDZ3HNRHVd0opR=19Qo4W4Q@mail.gmail.com/

V4:
 - Keep net_device "up" (IFF_UP) check.
 - Adjustment to handle bpf_redirect_peer() helper

Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
---
 include/linux/netdevice.h |   31 +++++++++++++++++++++++++++++--
 net/core/dev.c            |   19 ++-----------------
 net/core/filter.c         |   14 +++++++++++---
 3 files changed, 42 insertions(+), 22 deletions(-)

Comments

John Fastabend Oct. 30, 2020, 8:36 p.m. UTC | #1
Jesper Dangaard Brouer wrote:
> The use-case for dropping the MTU check when TC-BPF does redirect to
> ingress, is described by Eyal Birger in email[0]. The summary is the
> ability to increase packet size (e.g. with IPv6 headers for NAT64) and
> ingress redirect packet and let normal netstack fragment packet as needed.
> 
> [0] https://lore.kernel.org/netdev/CAHsH6Gug-hsLGHQ6N0wtixdOa85LDZ3HNRHVd0opR=19Qo4W4Q@mail.gmail.com/
> 
> V4:
>  - Keep net_device "up" (IFF_UP) check.
>  - Adjustment to handle bpf_redirect_peer() helper
> 
> Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
> ---
>  include/linux/netdevice.h |   31 +++++++++++++++++++++++++++++--
>  net/core/dev.c            |   19 ++-----------------
>  net/core/filter.c         |   14 +++++++++++---
>  3 files changed, 42 insertions(+), 22 deletions(-)
> 
> diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> index 964b494b0e8d..bd02ddab8dfe 100644
> --- a/include/linux/netdevice.h
> +++ b/include/linux/netdevice.h
> @@ -3891,11 +3891,38 @@ int dev_forward_skb(struct net_device *dev, struct sk_buff *skb);
>  bool is_skb_forwardable(const struct net_device *dev,
>  			const struct sk_buff *skb);
>  
> +static __always_inline bool __is_skb_forwardable(const struct net_device *dev,
> +						 const struct sk_buff *skb,
> +						 const bool check_mtu)

It looks like if check_mtu=false then this is just an interface up check.
Can we leave is_skb_forwardable logic alone and just change the spots where
this is called with false to something with a name that describes the check,
such as is_dev_up(dev). I think it will make this change smaller and the
code easier to read. Did I miss something?

> +{
> +	const u32 vlan_hdr_len = 4; /* VLAN_HLEN */
> +	unsigned int len;
> +
> +	if (!(dev->flags & IFF_UP))
> +		return false;
> +
> +	if (!check_mtu)
> +		return true;
> +
> +	len = dev->mtu + dev->hard_header_len + vlan_hdr_len;
> +	if (skb->len <= len)
> +		return true;
> +
> +	/* if TSO is enabled, we don't care about the length as the packet
> +	 * could be forwarded without being segmented before
> +	 */
> +	if (skb_is_gso(skb))
> +		return true;
> +
> +	return false;
> +}
> +
>  static __always_inline int ____dev_forward_skb(struct net_device *dev,
> -					       struct sk_buff *skb)
> +					       struct sk_buff *skb,
> +					       const bool check_mtu)
>  {

I guess you will get some duplication here if you have a dev_forward_skb()
and a dev_forward_skb_nocheck() or something. Take it or leave it. I know
I've added my share of bool swivel bits like this, but better to avoid
it if possible IMO.

Other than style aspects it looks correct to me.

>  	if (skb_orphan_frags(skb, GFP_ATOMIC) ||
> -	    unlikely(!is_skb_forwardable(dev, skb))) {
> +	    unlikely(!__is_skb_forwardable(dev, skb, check_mtu))) {
>  		atomic_long_inc(&dev->rx_dropped);
>  		kfree_skb(skb);
>  		return NET_RX_DROP;
> diff --git a/net/core/dev.c b/net/core/dev.c
> index 9499a414d67e..445ccf92c149 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -2188,28 +2188,13 @@ static inline void net_timestamp_set(struct sk_buff *skb)
>
Jesper Dangaard Brouer Nov. 2, 2020, 12:46 p.m. UTC | #2
On Fri, 30 Oct 2020 13:36:05 -0700
John Fastabend <john.fastabend@gmail.com> wrote:

> Jesper Dangaard Brouer wrote:
> > The use-case for dropping the MTU check when TC-BPF does redirect to
> > ingress, is described by Eyal Birger in email[0]. The summary is the
> > ability to increase packet size (e.g. with IPv6 headers for NAT64) and
> > ingress redirect packet and let normal netstack fragment packet as needed.
> > 
> > [0] https://lore.kernel.org/netdev/CAHsH6Gug-hsLGHQ6N0wtixdOa85LDZ3HNRHVd0opR=19Qo4W4Q@mail.gmail.com/
> > 
> > V4:
> >  - Keep net_device "up" (IFF_UP) check.
> >  - Adjustment to handle bpf_redirect_peer() helper
> > 
> > Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
> > ---
> >  include/linux/netdevice.h |   31 +++++++++++++++++++++++++++++--
> >  net/core/dev.c            |   19 ++-----------------
> >  net/core/filter.c         |   14 +++++++++++---
> >  3 files changed, 42 insertions(+), 22 deletions(-)
> > 
> > diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> > index 964b494b0e8d..bd02ddab8dfe 100644
> > --- a/include/linux/netdevice.h
> > +++ b/include/linux/netdevice.h
> > @@ -3891,11 +3891,38 @@ int dev_forward_skb(struct net_device *dev, struct sk_buff *skb);
> >  bool is_skb_forwardable(const struct net_device *dev,
> >  			const struct sk_buff *skb);
> >  
> > +static __always_inline bool __is_skb_forwardable(const struct net_device *dev,
> > +						 const struct sk_buff *skb,
> > +						 const bool check_mtu)  
> 
> It looks like if check_mtu=false then this is just an interface up check.
> Can we leave is_skb_forwardable logic alone and just change the spots where
> this is called with false to something with a name that describes the check,
> such as is_dev_up(dev). I think it will make this change smaller and the
> code easier to read. Did I miss something?

People should realized that this is constructed such, the compiler will
compile-time remove the actual argument (the const bool check_mtu).
And this propagates also to ____dev_forward_skb() where the call places
are also inlined.

Yes, this (check_mtu=false) is basically an interface up check, but the
only place it is used directly is in the ndo_get_peer_dev() case, and
reading the code I find it more readable that is says
__is_skb_forwardable because this is used as part of a forwarding step,
and is_dev_up() doesn't convey the intent in this use-case.


> > +{
> > +	const u32 vlan_hdr_len = 4; /* VLAN_HLEN */
> > +	unsigned int len;
> > +
> > +	if (!(dev->flags & IFF_UP))
> > +		return false;
> > +
> > +	if (!check_mtu)
> > +		return true;
> > +
> > +	len = dev->mtu + dev->hard_header_len + vlan_hdr_len;
> > +	if (skb->len <= len)
> > +		return true;
> > +
> > +	/* if TSO is enabled, we don't care about the length as the packet
> > +	 * could be forwarded without being segmented before
> > +	 */
> > +	if (skb_is_gso(skb))
> > +		return true;
> > +
> > +	return false;
> > +}
> > +
> >  static __always_inline int ____dev_forward_skb(struct net_device *dev,
> > -					       struct sk_buff *skb)
> > +					       struct sk_buff *skb,
> > +					       const bool check_mtu)
> >  {  
> 
> I guess you will get some duplication here if you have a dev_forward_skb()
> and a dev_forward_skb_nocheck() or something. Take it or leave it. I know
> I've added my share of bool swivel bits like this, but better to avoid
> it if possible IMO.

As I wrote the bool will actually get compile-time removed, so I don't
see that as problematic.  And I avoided replicating the code in more
places.

The problematic part (which you didn't comment) on is this:

On Fri, 30 Oct 2020 17:51:07 +0100
Jesper Dangaard Brouer <brouer@redhat.com> wrote:

> diff --git a/net/core/filter.c b/net/core/filter.c
> index bd4a416bd9ad..71b78b8d443c 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -2083,13 +2083,21 @@ static const struct bpf_func_proto bpf_csum_level_proto = {
>  
>  static inline int __bpf_rx_skb(struct net_device *dev, struct sk_buff *skb)
>  {
> -	return dev_forward_skb(dev, skb);
> +	int ret = ____dev_forward_skb(dev, skb, false);
> +
> +	if (likely(!ret)) {
> +		skb->protocol = eth_type_trans(skb, dev);
> +		skb_postpull_rcsum(skb, eth_hdr(skb), ETH_HLEN);
> +		ret = netif_rx(skb);
> +	}
> +
> +	return ret;
>  }

I'm replicating two lines from dev_forward_skb(), but I couldn't find a
way to avoid this, without causing larger code changes (and slower code).



> Other than style aspects it looks correct to me.
> 
> >  	if (skb_orphan_frags(skb, GFP_ATOMIC) ||
> > -	    unlikely(!is_skb_forwardable(dev, skb))) {
> > +	    unlikely(!__is_skb_forwardable(dev, skb, check_mtu))) {
> >  		atomic_long_inc(&dev->rx_dropped);
> >  		kfree_skb(skb);
> >  		return NET_RX_DROP;
> > diff --git a/net/core/dev.c b/net/core/dev.c
> > index 9499a414d67e..445ccf92c149 100644
> > --- a/net/core/dev.c
> > +++ b/net/core/dev.c
> > @@ -2188,28 +2188,13 @@ static inline void net_timestamp_set(struct sk_buff *skb)
> >    
>
John Fastabend Nov. 2, 2020, 4:23 p.m. UTC | #3
Jesper Dangaard Brouer wrote:
> On Fri, 30 Oct 2020 13:36:05 -0700
> John Fastabend <john.fastabend@gmail.com> wrote:
> 
> > Jesper Dangaard Brouer wrote:
> > > The use-case for dropping the MTU check when TC-BPF does redirect to
> > > ingress, is described by Eyal Birger in email[0]. The summary is the
> > > ability to increase packet size (e.g. with IPv6 headers for NAT64) and
> > > ingress redirect packet and let normal netstack fragment packet as needed.
> > > 
> > > [0] https://lore.kernel.org/netdev/CAHsH6Gug-hsLGHQ6N0wtixdOa85LDZ3HNRHVd0opR=19Qo4W4Q@mail.gmail.com/
> > > 
> > > V4:
> > >  - Keep net_device "up" (IFF_UP) check.
> > >  - Adjustment to handle bpf_redirect_peer() helper
> > > 
> > > Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
> > > ---
> > >  include/linux/netdevice.h |   31 +++++++++++++++++++++++++++++--
> > >  net/core/dev.c            |   19 ++-----------------
> > >  net/core/filter.c         |   14 +++++++++++---
> > >  3 files changed, 42 insertions(+), 22 deletions(-)
> > > 
> > > diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> > > index 964b494b0e8d..bd02ddab8dfe 100644
> > > --- a/include/linux/netdevice.h
> > > +++ b/include/linux/netdevice.h
> > > @@ -3891,11 +3891,38 @@ int dev_forward_skb(struct net_device *dev, struct sk_buff *skb);
> > >  bool is_skb_forwardable(const struct net_device *dev,
> > >  			const struct sk_buff *skb);
> > >  
> > > +static __always_inline bool __is_skb_forwardable(const struct net_device *dev,
> > > +						 const struct sk_buff *skb,
> > > +						 const bool check_mtu)  
> > 
> > It looks like if check_mtu=false then this is just an interface up check.
> > Can we leave is_skb_forwardable logic alone and just change the spots where
> > this is called with false to something with a name that describes the check,
> > such as is_dev_up(dev). I think it will make this change smaller and the
> > code easier to read. Did I miss something?
> 
> People should realized that this is constructed such, the compiler will
> compile-time remove the actual argument (the const bool check_mtu).
> And this propagates also to ____dev_forward_skb() where the call places
> are also inlined.

The comment was about human reading the code not what gets generated
by the compiler.

> 
> Yes, this (check_mtu=false) is basically an interface up check, but the
> only place it is used directly is in the ndo_get_peer_dev() case, and
> reading the code I find it more readable that is says
> __is_skb_forwardable because this is used as part of a forwarding step,
> and is_dev_up() doesn't convey the intent in this use-case.

OK.

[...]

> 
> > diff --git a/net/core/filter.c b/net/core/filter.c
> > index bd4a416bd9ad..71b78b8d443c 100644
> > --- a/net/core/filter.c
> > +++ b/net/core/filter.c
> > @@ -2083,13 +2083,21 @@ static const struct bpf_func_proto bpf_csum_level_proto = {
> >  
> >  static inline int __bpf_rx_skb(struct net_device *dev, struct sk_buff *skb)
> >  {
> > -	return dev_forward_skb(dev, skb);
> > +	int ret = ____dev_forward_skb(dev, skb, false);
> > +
> > +	if (likely(!ret)) {
> > +		skb->protocol = eth_type_trans(skb, dev);
> > +		skb_postpull_rcsum(skb, eth_hdr(skb), ETH_HLEN);
> > +		ret = netif_rx(skb);
> > +	}
> > +
> > +	return ret;
> >  }
> 
> I'm replicating two lines from dev_forward_skb(), but I couldn't find a
> way to avoid this, without causing larger code changes (and slower code).
> 

OK looks good to me then.

> 
> 
> > Other than style aspects it looks correct to me.
> > 
> > >  	if (skb_orphan_frags(skb, GFP_ATOMIC) ||
> > > -	    unlikely(!is_skb_forwardable(dev, skb))) {
> > > +	    unlikely(!__is_skb_forwardable(dev, skb, check_mtu))) {
> > >  		atomic_long_inc(&dev->rx_dropped);
> > >  		kfree_skb(skb);
> > >  		return NET_RX_DROP;
> > > diff --git a/net/core/dev.c b/net/core/dev.c
> > > index 9499a414d67e..445ccf92c149 100644
> > > --- a/net/core/dev.c
> > > +++ b/net/core/dev.c
> > > @@ -2188,28 +2188,13 @@ static inline void net_timestamp_set(struct sk_buff *skb)
> > >    
> > 
> 
> 
> 
> -- 
> Best regards,
>   Jesper Dangaard Brouer
>   MSc.CS, Principal Kernel Engineer at Red Hat
>   LinkedIn: http://www.linkedin.com/in/brouer
>
diff mbox series

Patch

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 964b494b0e8d..bd02ddab8dfe 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -3891,11 +3891,38 @@  int dev_forward_skb(struct net_device *dev, struct sk_buff *skb);
 bool is_skb_forwardable(const struct net_device *dev,
 			const struct sk_buff *skb);
 
+static __always_inline bool __is_skb_forwardable(const struct net_device *dev,
+						 const struct sk_buff *skb,
+						 const bool check_mtu)
+{
+	const u32 vlan_hdr_len = 4; /* VLAN_HLEN */
+	unsigned int len;
+
+	if (!(dev->flags & IFF_UP))
+		return false;
+
+	if (!check_mtu)
+		return true;
+
+	len = dev->mtu + dev->hard_header_len + vlan_hdr_len;
+	if (skb->len <= len)
+		return true;
+
+	/* if TSO is enabled, we don't care about the length as the packet
+	 * could be forwarded without being segmented before
+	 */
+	if (skb_is_gso(skb))
+		return true;
+
+	return false;
+}
+
 static __always_inline int ____dev_forward_skb(struct net_device *dev,
-					       struct sk_buff *skb)
+					       struct sk_buff *skb,
+					       const bool check_mtu)
 {
 	if (skb_orphan_frags(skb, GFP_ATOMIC) ||
-	    unlikely(!is_skb_forwardable(dev, skb))) {
+	    unlikely(!__is_skb_forwardable(dev, skb, check_mtu))) {
 		atomic_long_inc(&dev->rx_dropped);
 		kfree_skb(skb);
 		return NET_RX_DROP;
diff --git a/net/core/dev.c b/net/core/dev.c
index 9499a414d67e..445ccf92c149 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -2188,28 +2188,13 @@  static inline void net_timestamp_set(struct sk_buff *skb)
 
 bool is_skb_forwardable(const struct net_device *dev, const struct sk_buff *skb)
 {
-	unsigned int len;
-
-	if (!(dev->flags & IFF_UP))
-		return false;
-
-	len = dev->mtu + dev->hard_header_len + VLAN_HLEN;
-	if (skb->len <= len)
-		return true;
-
-	/* if TSO is enabled, we don't care about the length as the packet
-	 * could be forwarded without being segmented before
-	 */
-	if (skb_is_gso(skb))
-		return true;
-
-	return false;
+	return __is_skb_forwardable(dev, skb, true);
 }
 EXPORT_SYMBOL_GPL(is_skb_forwardable);
 
 int __dev_forward_skb(struct net_device *dev, struct sk_buff *skb)
 {
-	int ret = ____dev_forward_skb(dev, skb);
+	int ret = ____dev_forward_skb(dev, skb, true);
 
 	if (likely(!ret)) {
 		skb->protocol = eth_type_trans(skb, dev);
diff --git a/net/core/filter.c b/net/core/filter.c
index bd4a416bd9ad..71b78b8d443c 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -2083,13 +2083,21 @@  static const struct bpf_func_proto bpf_csum_level_proto = {
 
 static inline int __bpf_rx_skb(struct net_device *dev, struct sk_buff *skb)
 {
-	return dev_forward_skb(dev, skb);
+	int ret = ____dev_forward_skb(dev, skb, false);
+
+	if (likely(!ret)) {
+		skb->protocol = eth_type_trans(skb, dev);
+		skb_postpull_rcsum(skb, eth_hdr(skb), ETH_HLEN);
+		ret = netif_rx(skb);
+	}
+
+	return ret;
 }
 
 static inline int __bpf_rx_skb_no_mac(struct net_device *dev,
 				      struct sk_buff *skb)
 {
-	int ret = ____dev_forward_skb(dev, skb);
+	int ret = ____dev_forward_skb(dev, skb, false);
 
 	if (likely(!ret)) {
 		skb->dev = dev;
@@ -2480,7 +2488,7 @@  int skb_do_redirect(struct sk_buff *skb)
 			goto out_drop;
 		dev = ops->ndo_get_peer_dev(dev);
 		if (unlikely(!dev ||
-			     !is_skb_forwardable(dev, skb) ||
+			     !__is_skb_forwardable(dev, skb, false) ||
 			     net_eq(net, dev_net(dev))))
 			goto out_drop;
 		skb->dev = dev;