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Subject[PATCH net-next] drivers/net/wan/hdlc_fr: Correctly handle special skb->protocol values
Date
The fr_hard_header function is used to prepend the header to skbs before
transmission. It is used in 3 situations:
1) When a control packet is generated internally in this driver;
2) When a user sends an skb on an Ethernet-emulating PVC device;
3) When a user sends an skb on a normal PVC device.

These 3 situations need to be handled differently by fr_hard_header.
Different headers should be prepended to the skb in different situations.

Currently fr_hard_header distinguishes these 3 situations using
skb->protocol. For situation 1 and 2, a special skb->protocol value
will be assigned before calling fr_hard_header, so that it can recognize
these 2 situations. All skb->protocol values other than these special ones
are treated by fr_hard_header as situation 3.

However, it is possible that in situation 3, the user sends an skb with
one of the special skb->protocol values. In this case, fr_hard_header
would incorrectly treat it as situation 1 or 2.

This patch tries to solve this issue by using skb->dev instead of
skb->protocol to distinguish between these 3 situations. For situation
1, skb->dev would be NULL; for situation 2, skb->dev->type would be
ARPHRD_ETHER; and for situation 3, skb->dev->type would be ARPHRD_DLCI.

This way fr_hard_header would be able to distinguish these 3 situations
correctly regardless what skb->protocol value the user tries to use in
situation 3.

Cc: Krzysztof Halasa <khc@pm.waw.pl>
Signed-off-by: Xie He <xie.he.0141@gmail.com>
---
drivers/net/wan/hdlc_fr.c | 98 ++++++++++++++++++++-------------------
1 file changed, 51 insertions(+), 47 deletions(-)

diff --git a/drivers/net/wan/hdlc_fr.c b/drivers/net/wan/hdlc_fr.c
index d6cfd51613ed..3a44dad87602 100644
--- a/drivers/net/wan/hdlc_fr.c
+++ b/drivers/net/wan/hdlc_fr.c
@@ -273,63 +273,69 @@ static inline struct net_device **get_dev_p(struct pvc_device *pvc,

static int fr_hard_header(struct sk_buff **skb_p, u16 dlci)
{
- u16 head_len;
struct sk_buff *skb = *skb_p;

- switch (skb->protocol) {
- case cpu_to_be16(NLPID_CCITT_ANSI_LMI):
- head_len = 4;
- skb_push(skb, head_len);
- skb->data[3] = NLPID_CCITT_ANSI_LMI;
- break;
-
- case cpu_to_be16(NLPID_CISCO_LMI):
- head_len = 4;
- skb_push(skb, head_len);
- skb->data[3] = NLPID_CISCO_LMI;
- break;
-
- case cpu_to_be16(ETH_P_IP):
- head_len = 4;
- skb_push(skb, head_len);
- skb->data[3] = NLPID_IP;
- break;
-
- case cpu_to_be16(ETH_P_IPV6):
- head_len = 4;
- skb_push(skb, head_len);
- skb->data[3] = NLPID_IPV6;
- break;
-
- case cpu_to_be16(ETH_P_802_3):
- head_len = 10;
- if (skb_headroom(skb) < head_len) {
- struct sk_buff *skb2 = skb_realloc_headroom(skb,
- head_len);
+ if (!skb->dev) { /* Control packets */
+ switch (dlci) {
+ case LMI_CCITT_ANSI_DLCI:
+ skb_push(skb, 4);
+ skb->data[3] = NLPID_CCITT_ANSI_LMI;
+ break;
+
+ case LMI_CISCO_DLCI:
+ skb_push(skb, 4);
+ skb->data[3] = NLPID_CISCO_LMI;
+ break;
+
+ default:
+ return -EINVAL;
+ }
+
+ } else if (skb->dev->type == ARPHRD_DLCI) {
+ switch (skb->protocol) {
+ case htons(ETH_P_IP):
+ skb_push(skb, 4);
+ skb->data[3] = NLPID_IP;
+ break;
+
+ case htons(ETH_P_IPV6):
+ skb_push(skb, 4);
+ skb->data[3] = NLPID_IPV6;
+ break;
+
+ default:
+ skb_push(skb, 10);
+ skb->data[3] = FR_PAD;
+ skb->data[4] = NLPID_SNAP;
+ /* OUI 00-00-00 indicates an Ethertype follows */
+ skb->data[5] = 0x00;
+ skb->data[6] = 0x00;
+ skb->data[7] = 0x00;
+ /* This should be an Ethertype: */
+ *(__be16 *)(skb->data + 8) = skb->protocol;
+ }
+
+ } else if (skb->dev->type == ARPHRD_ETHER) {
+ if (skb_headroom(skb) < 10) {
+ struct sk_buff *skb2 = skb_realloc_headroom(skb, 10);
if (!skb2)
return -ENOBUFS;
dev_kfree_skb(skb);
skb = *skb_p = skb2;
}
- skb_push(skb, head_len);
+ skb_push(skb, 10);
skb->data[3] = FR_PAD;
skb->data[4] = NLPID_SNAP;
- skb->data[5] = FR_PAD;
+ /* OUI 00-80-C2 stands for the 802.1 organization */
+ skb->data[5] = 0x00;
skb->data[6] = 0x80;
skb->data[7] = 0xC2;
+ /* PID 00-07 stands for Ethernet frames without FCS */
skb->data[8] = 0x00;
- skb->data[9] = 0x07; /* bridged Ethernet frame w/out FCS */
- break;
+ skb->data[9] = 0x07;

- default:
- head_len = 10;
- skb_push(skb, head_len);
- skb->data[3] = FR_PAD;
- skb->data[4] = NLPID_SNAP;
- skb->data[5] = FR_PAD;
- skb->data[6] = FR_PAD;
- skb->data[7] = FR_PAD;
- *(__be16*)(skb->data + 8) = skb->protocol;
+ } else {
+ return -EINVAL;
}

dlci_to_q922(skb->data, dlci);
@@ -425,8 +431,8 @@ static netdev_tx_t pvc_xmit(struct sk_buff *skb, struct net_device *dev)
skb_put(skb, pad);
memset(skb->data + len, 0, pad);
}
- skb->protocol = cpu_to_be16(ETH_P_802_3);
}
+ skb->dev = dev;
if (!fr_hard_header(&skb, pvc->dlci)) {
dev->stats.tx_bytes += skb->len;
dev->stats.tx_packets++;
@@ -494,10 +500,8 @@ static void fr_lmi_send(struct net_device *dev, int fullrep)
memset(skb->data, 0, len);
skb_reserve(skb, 4);
if (lmi == LMI_CISCO) {
- skb->protocol = cpu_to_be16(NLPID_CISCO_LMI);
fr_hard_header(&skb, LMI_CISCO_DLCI);
} else {
- skb->protocol = cpu_to_be16(NLPID_CCITT_ANSI_LMI);
fr_hard_header(&skb, LMI_CCITT_ANSI_DLCI);
}
data = skb_tail_pointer(skb);
--
2.25.1
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