[PATCH net-next v7 0/5] net: hdlc_fr: Improve fr_rx and add support for any Ethertype

[PATCH net-next v7 0/5] net: hdlc_fr: Improve fr_rx and add support for any Ethertype

[Xie He]

The main purpose of this series is the last patch. The previous 4 patches
are just code clean-ups so that the last patch will not make the code too
messy. The patches must be applied in sequence.

The receiving code of this driver doesn't support arbitrary Ethertype
values. It only recognizes a few known Ethertypes when receiving and drops
skbs with other Ethertypes.

However, the standard document RFC 2427 allows Frame Relay to support any
Ethertype values. This series adds support for this.

Change from v6:
Remove the explanation about why only a 2-byte address field is accepted
because I think it is inadequate and unnecessary.

Change from v5:
Small fix to the commit messages.

Change from v4:
Drop the change related to the stats.rx_dropped count.
Improve the commit message by stating why only a 2-byte address field
is accepted.

Change from v3:
Split the last patch into 2 patches.
Improve the commit message about the stats.rx_dropped count.

Change from v2:
Small fix to the commit messages.

Change from v1:
Small fix to the commit messages.

Xie He (5):
  net: hdlc_fr: Simpify fr_rx by using "goto rx_drop" to drop frames
  net: hdlc_fr: Change the use of "dev" in fr_rx to make the code
    cleaner
  net: hdlc_fr: Do skb_reset_mac_header for skbs received on normal PVC
    devices
  net: hdlc_fr: Improve the initial checks when we receive an skb
  net: hdlc_fr: Add support for any Ethertype

 drivers/net/wan/hdlc_fr.c | 118 +++++++++++++++++++++++---------------
 1 file changed, 72 insertions(+), 46 deletions(-)

-- 
2.27.0

[PATCH net-next v7 1/5] net: hdlc_fr: Simpify fr_rx by using "goto rx_drop" to drop frames

[Xie He]

When the fr_rx function drops a received frame (because the protocol type
is not supported, or because the PVC virtual device that corresponds to
the DLCI number and the protocol type doesn't exist), the function frees
the skb and returns.

The code for freeing the skb and returning is repeated several times, this
patch uses "goto rx_drop" to replace them so that the code looks cleaner.

Cc: Krzysztof Halasa <khc@pm.waw.pl>
Cc: Willem de Bruijn <willemdebruijn.kernel@gmail.com>
Signed-off-by: Xie He <xie.he.0141@gmail.com>
---
 drivers/net/wan/hdlc_fr.c | 15 ++++++---------
 1 file changed, 6 insertions(+), 9 deletions(-)

diff --git a/drivers/net/wan/hdlc_fr.c b/drivers/net/wan/hdlc_fr.c
index 409e5a7ad8e2..4db0e01b96a9 100644
--- a/drivers/net/wan/hdlc_fr.c
+++ b/drivers/net/wan/hdlc_fr.c
@@ -904,8 +904,7 @@ static int fr_rx(struct sk_buff *skb)
 		netdev_info(frad, "No PVC for received frame's DLCI %d\n",
 			    dlci);
 #endif
-		dev_kfree_skb_any(skb);
-		return NET_RX_DROP;
+		goto rx_drop;
 	}
 
 	if (pvc->state.fecn != fh->fecn) {
@@ -963,14 +962,12 @@ static int fr_rx(struct sk_buff *skb)
 		default:
 			netdev_info(frad, "Unsupported protocol, OUI=%x PID=%x\n",
 				    oui, pid);
-			dev_kfree_skb_any(skb);
-			return NET_RX_DROP;
+			goto rx_drop;
 		}
 	} else {
 		netdev_info(frad, "Unsupported protocol, NLPID=%x length=%i\n",
 			    data[3], skb->len);
-		dev_kfree_skb_any(skb);
-		return NET_RX_DROP;
+		goto rx_drop;
 	}
 
 	if (dev) {
@@ -982,12 +979,12 @@ static int fr_rx(struct sk_buff *skb)
 		netif_rx(skb);
 		return NET_RX_SUCCESS;
 	} else {
-		dev_kfree_skb_any(skb);
-		return NET_RX_DROP;
+		goto rx_drop;
 	}
 
- rx_error:
+rx_error:
 	frad->stats.rx_errors++; /* Mark error */
+rx_drop:
 	dev_kfree_skb_any(skb);
 	return NET_RX_DROP;
 }
-- 
2.27.0

[PATCH net-next v7 2/5] net: hdlc_fr: Change the use of "dev" in fr_rx to make the code cleaner

[Xie He]

The eth_type_trans function is called when we receive frames carrying
Ethernet frames. This function expects a non-NULL pointer as an argument,
and assigns it directly to skb->dev.

However, the code handling other types of frames first assigns the pointer
to "dev", and then at the end checks whether the value is NULL, and if it
is not NULL, assigns it to skb->dev.

The two flows are different. Mixing them in this function makes the code
messy. It's better that we convert the second flow to align with how
eth_type_trans does things.

So this patch changes the code to: first make sure the pointer is not
NULL, then assign it directly to skb->dev. "dev" is no longer needed until
the end where we use it to update stats.

Cc: Krzysztof Halasa <khc@pm.waw.pl>
Cc: Willem de Bruijn <willemdebruijn.kernel@gmail.com>
Signed-off-by: Xie He <xie.he.0141@gmail.com>
---
 drivers/net/wan/hdlc_fr.c | 37 ++++++++++++++++++++-----------------
 1 file changed, 20 insertions(+), 17 deletions(-)

diff --git a/drivers/net/wan/hdlc_fr.c b/drivers/net/wan/hdlc_fr.c
index 4db0e01b96a9..71ee9b60d91b 100644
--- a/drivers/net/wan/hdlc_fr.c
+++ b/drivers/net/wan/hdlc_fr.c
@@ -880,7 +880,7 @@ static int fr_rx(struct sk_buff *skb)
 	u8 *data = skb->data;
 	u16 dlci;
 	struct pvc_device *pvc;
-	struct net_device *dev = NULL;
+	struct net_device *dev;
 
 	if (skb->len <= 4 || fh->ea1 || data[2] != FR_UI)
 		goto rx_error;
@@ -930,13 +930,17 @@ static int fr_rx(struct sk_buff *skb)
 	}
 
 	if (data[3] == NLPID_IP) {
+		if (!pvc->main)
+			goto rx_drop;
 		skb_pull(skb, 4); /* Remove 4-byte header (hdr, UI, NLPID) */
-		dev = pvc->main;
+		skb->dev = pvc->main;
 		skb->protocol = htons(ETH_P_IP);
 
 	} else if (data[3] == NLPID_IPV6) {
+		if (!pvc->main)
+			goto rx_drop;
 		skb_pull(skb, 4); /* Remove 4-byte header (hdr, UI, NLPID) */
-		dev = pvc->main;
+		skb->dev = pvc->main;
 		skb->protocol = htons(ETH_P_IPV6);
 
 	} else if (skb->len > 10 && data[3] == FR_PAD &&
@@ -950,13 +954,16 @@ static int fr_rx(struct sk_buff *skb)
 		case ETH_P_IPX:
 		case ETH_P_IP:	/* a long variant */
 		case ETH_P_IPV6:
-			dev = pvc->main;
+			if (!pvc->main)
+				goto rx_drop;
+			skb->dev = pvc->main;
 			skb->protocol = htons(pid);
 			break;
 
 		case 0x80C20007: /* bridged Ethernet frame */
-			if ((dev = pvc->ether) != NULL)
-				skb->protocol = eth_type_trans(skb, dev);
+			if (!pvc->ether)
+				goto rx_drop;
+			skb->protocol = eth_type_trans(skb, pvc->ether);
 			break;
 
 		default:
@@ -970,17 +977,13 @@ static int fr_rx(struct sk_buff *skb)
 		goto rx_drop;
 	}
 
-	if (dev) {
-		dev->stats.rx_packets++; /* PVC traffic */
-		dev->stats.rx_bytes += skb->len;
-		if (pvc->state.becn)
-			dev->stats.rx_compressed++;
-		skb->dev = dev;
-		netif_rx(skb);
-		return NET_RX_SUCCESS;
-	} else {
-		goto rx_drop;
-	}
+	dev = skb->dev;
+	dev->stats.rx_packets++; /* PVC traffic */
+	dev->stats.rx_bytes += skb->len;
+	if (pvc->state.becn)
+		dev->stats.rx_compressed++;
+	netif_rx(skb);
+	return NET_RX_SUCCESS;
 
 rx_error:
 	frad->stats.rx_errors++; /* Mark error */
-- 
2.27.0

[PATCH net-next v7 3/5] net: hdlc_fr: Do skb_reset_mac_header for skbs received on normal PVC devices

[Xie He]

When an skb is received on a normal (non-Ethernet-emulating) PVC device,
call skb_reset_mac_header before we pass it to upper layers.

This is because normal PVC devices don't have header_ops, so any header we
have would not be visible to upper layer code when sending, so the header
shouldn't be visible to upper layer code when receiving, either.

Cc: Krzysztof Halasa <khc@pm.waw.pl>
Cc: Willem de Bruijn <willemdebruijn.kernel@gmail.com>
Signed-off-by: Xie He <xie.he.0141@gmail.com>
---
 drivers/net/wan/hdlc_fr.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/net/wan/hdlc_fr.c b/drivers/net/wan/hdlc_fr.c
index 71ee9b60d91b..eb83116aa9df 100644
--- a/drivers/net/wan/hdlc_fr.c
+++ b/drivers/net/wan/hdlc_fr.c
@@ -935,6 +935,7 @@ static int fr_rx(struct sk_buff *skb)
 		skb_pull(skb, 4); /* Remove 4-byte header (hdr, UI, NLPID) */
 		skb->dev = pvc->main;
 		skb->protocol = htons(ETH_P_IP);
+		skb_reset_mac_header(skb);
 
 	} else if (data[3] == NLPID_IPV6) {
 		if (!pvc->main)
@@ -942,6 +943,7 @@ static int fr_rx(struct sk_buff *skb)
 		skb_pull(skb, 4); /* Remove 4-byte header (hdr, UI, NLPID) */
 		skb->dev = pvc->main;
 		skb->protocol = htons(ETH_P_IPV6);
+		skb_reset_mac_header(skb);
 
 	} else if (skb->len > 10 && data[3] == FR_PAD &&
 		   data[4] == NLPID_SNAP && data[5] == FR_PAD) {
@@ -958,6 +960,7 @@ static int fr_rx(struct sk_buff *skb)
 				goto rx_drop;
 			skb->dev = pvc->main;
 			skb->protocol = htons(pid);
+			skb_reset_mac_header(skb);
 			break;
 
 		case 0x80C20007: /* bridged Ethernet frame */
-- 
2.27.0

[PATCH net-next v7 4/5] net: hdlc_fr: Improve the initial checks when we receive an skb

[Xie He]

1.
Change the skb->len check from "<= 4" to "< 4".
At first we only need to ensure a 4-byte header is present. We indeed
normally need the 5th byte, too, but it'd be more logical and cleaner
to check its existence when we actually need it.

2.
Add an fh->ea2 check to the initial checks in fr_rx. fh->ea2 == 1 means
the second address byte is the final address byte. We only support the
case where the address length is 2 bytes.

Cc: Krzysztof Halasa <khc@pm.waw.pl>
Cc: Willem de Bruijn <willemdebruijn.kernel@gmail.com>
Signed-off-by: Xie He <xie.he.0141@gmail.com>
---
 drivers/net/wan/hdlc_fr.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/wan/hdlc_fr.c b/drivers/net/wan/hdlc_fr.c
index eb83116aa9df..98444f1d8cc3 100644
--- a/drivers/net/wan/hdlc_fr.c
+++ b/drivers/net/wan/hdlc_fr.c
@@ -882,7 +882,7 @@ static int fr_rx(struct sk_buff *skb)
 	struct pvc_device *pvc;
 	struct net_device *dev;
 
-	if (skb->len <= 4 || fh->ea1 || data[2] != FR_UI)
+	if (skb->len < 4 || fh->ea1 || !fh->ea2 || data[2] != FR_UI)
 		goto rx_error;
 
 	dlci = q922_to_dlci(skb->data);
-- 
2.27.0

[PATCH net-next v7 5/5] net: hdlc_fr: Add support for any Ethertype

[Xie He]

Change the fr_rx function to make this driver support any Ethertype
when receiving skbs on normal (non-Ethernet-emulating) PVC devices.
(This driver is already able to handle any Ethertype when sending.)

Originally in the fr_rx function, the code that parses the long (10-byte)
header only recognizes a few Ethertype values and drops frames with other
Ethertype values. This patch replaces this code to make fr_rx support
any Ethertype. This patch also creates a new function fr_snap_parse as
part of the new code.

Cc: Krzysztof Halasa <khc@pm.waw.pl>
Cc: Willem de Bruijn <willemdebruijn.kernel@gmail.com>
Signed-off-by: Xie He <xie.he.0141@gmail.com>
---
 drivers/net/wan/hdlc_fr.c | 75 +++++++++++++++++++++++++--------------
 1 file changed, 49 insertions(+), 26 deletions(-)

diff --git a/drivers/net/wan/hdlc_fr.c b/drivers/net/wan/hdlc_fr.c
index 98444f1d8cc3..0720f5f92caa 100644
--- a/drivers/net/wan/hdlc_fr.c
+++ b/drivers/net/wan/hdlc_fr.c
@@ -871,6 +871,45 @@ static int fr_lmi_recv(struct net_device *dev, struct sk_buff *skb)
 	return 0;
 }
 
+static int fr_snap_parse(struct sk_buff *skb, struct pvc_device *pvc)
+{
+	/* OUI 00-00-00 indicates an Ethertype follows */
+	if (skb->data[0] == 0x00 &&
+	    skb->data[1] == 0x00 &&
+	    skb->data[2] == 0x00) {
+		if (!pvc->main)
+			return -1;
+		skb->dev = pvc->main;
+		skb->protocol = *(__be16 *)(skb->data + 3); /* Ethertype */
+		skb_pull(skb, 5);
+		skb_reset_mac_header(skb);
+		return 0;
+
+	/* OUI 00-80-C2 stands for the 802.1 organization */
+	} else if (skb->data[0] == 0x00 &&
+		   skb->data[1] == 0x80 &&
+		   skb->data[2] == 0xC2) {
+		/* PID 00-07 stands for Ethernet frames without FCS */
+		if (skb->data[3] == 0x00 &&
+		    skb->data[4] == 0x07) {
+			if (!pvc->ether)
+				return -1;
+			skb_pull(skb, 5);
+			if (skb->len < ETH_HLEN)
+				return -1;
+			skb->protocol = eth_type_trans(skb, pvc->ether);
+			return 0;
+
+		/* PID unsupported */
+		} else {
+			return -1;
+		}
+
+	/* OUI unsupported */
+	} else {
+		return -1;
+	}
+}
 
 static int fr_rx(struct sk_buff *skb)
 {
@@ -945,35 +984,19 @@ static int fr_rx(struct sk_buff *skb)
 		skb->protocol = htons(ETH_P_IPV6);
 		skb_reset_mac_header(skb);
 
-	} else if (skb->len > 10 && data[3] == FR_PAD &&
-		   data[4] == NLPID_SNAP && data[5] == FR_PAD) {
-		u16 oui = ntohs(*(__be16*)(data + 6));
-		u16 pid = ntohs(*(__be16*)(data + 8));
-		skb_pull(skb, 10);
-
-		switch ((((u32)oui) << 16) | pid) {
-		case ETH_P_ARP: /* routed frame with SNAP */
-		case ETH_P_IPX:
-		case ETH_P_IP:	/* a long variant */
-		case ETH_P_IPV6:
-			if (!pvc->main)
-				goto rx_drop;
-			skb->dev = pvc->main;
-			skb->protocol = htons(pid);
-			skb_reset_mac_header(skb);
-			break;
-
-		case 0x80C20007: /* bridged Ethernet frame */
-			if (!pvc->ether)
+	} else if (data[3] == FR_PAD) {
+		if (skb->len < 5)
+			goto rx_error;
+		if (data[4] == NLPID_SNAP) { /* A SNAP header follows */
+			skb_pull(skb, 5);
+			if (skb->len < 5) /* Incomplete SNAP header */
+				goto rx_error;
+			if (fr_snap_parse(skb, pvc))
 				goto rx_drop;
-			skb->protocol = eth_type_trans(skb, pvc->ether);
-			break;
-
-		default:
-			netdev_info(frad, "Unsupported protocol, OUI=%x PID=%x\n",
-				    oui, pid);
+		} else {
 			goto rx_drop;
 		}
+
 	} else {
 		netdev_info(frad, "Unsupported protocol, NLPID=%x length=%i\n",
 			    data[3], skb->len);
-- 
2.27.0

Re: [PATCH net-next v7 0/5] net: hdlc_fr: Improve fr_rx and add support for any Ethertype

[Jakub Kicinski]

On Sat, 31 Oct 2020 11:10:38 -0700 Xie He wrote:
> The main purpose of this series is the last patch. The previous 4 patches
> are just code clean-ups so that the last patch will not make the code too
> messy. The patches must be applied in sequence.
> 
> The receiving code of this driver doesn't support arbitrary Ethertype
> values. It only recognizes a few known Ethertypes when receiving and drops
> skbs with other Ethertypes.
> 
> However, the standard document RFC 2427 allows Frame Relay to support any
> Ethertype values. This series adds support for this.

Applied, but going forward please limit any refactoring and extensions
to the HDLC code. I thought you are actually using it. If that's not
the case let's leave the code be, it's likely going to be removed in 
a few years time.

Re: [PATCH net-next v7 0/5] net: hdlc_fr: Improve fr_rx and add support for any Ethertype

[Xie He]

On Tue, Nov 3, 2020 at 3:22 PM Jakub Kicinski <kuba@kernel.org> wrote:
>
> Applied, but going forward please limit any refactoring and extensions
> to the HDLC code. I thought you are actually using it. If that's not
> the case let's leave the code be, it's likely going to be removed in
> a few years time.

OK. I understand.

Thanks!

Re: [PATCH net-next v7 0/5] net: hdlc_fr: Improve fr_rx and add support for any Ethertype

[Xie He]

On Tue, Nov 3, 2020 at 6:03 PM Xie He <xie.he.0141@gmail.com> wrote:
>
> On Tue, Nov 3, 2020 at 3:22 PM Jakub Kicinski <kuba@kernel.org> wrote:
> >
> > Applied, but going forward please limit any refactoring and extensions
> > to the HDLC code. I thought you are actually using it. If that's not
> > the case let's leave the code be, it's likely going to be removed in
> > a few years time.
>
> OK. I understand.
>
> Thanks!

The HDLC layer is still used by X.25 people (to be precise, Martin
Schiller <ms@dev.tdt.de>). Although we currently have three X.25
drivers in the kernel (lapbether, x25_asy, hdlc_x25), it seems to me
that only hdlc_x25 is used in the real world. So I guess the HDLC
layer will be there as long as the X.25 stack is still there.