This new ioctl allows two ppp channels to be bridged together: frames
arriving in one channel are transmitted in the other channel and vice
versa.
The practical use for this is primarily to support the L2TP Access
Concentrator use-case. The end-user session is presented as a ppp
channel (typically PPPoE, although it could be e.g. PPPoA, or even PPP
over a serial link) and is switched into a PPPoL2TP session for
transmission to the LNS. At the LNS the PPP session is terminated in
the ISP's network.
When a PPP channel is bridged to another it takes a reference on the
other's struct ppp_file. This reference is dropped when the channel is
unregistered: if the dereference causes the bridged channel's reference
count to reach zero it is destroyed at that point.
---
drivers/net/ppp/ppp_generic.c | 35 +++++++++++++++++++++++++++++++++-
include/uapi/linux/ppp-ioctl.h | 1 +
2 files changed, 35 insertions(+), 1 deletion(-)
diff --git a/drivers/net/ppp/ppp_generic.c b/drivers/net/ppp/ppp_generic.c
index 7d005896a0f9..d893bf4470f4 100644
--- a/drivers/net/ppp/ppp_generic.c
+++ b/drivers/net/ppp/ppp_generic.c
@@ -175,6 +175,7 @@ struct channel {
struct net *chan_net; /* the net channel belongs to */
struct list_head clist; /* link in list of channels per unit */
rwlock_t upl; /* protects `ppp' */
+ struct channel *bridge; /* "bridged" ppp channel */
#ifdef CONFIG_PPP_MULTILINK
u8 avail; /* flag used in multilink stuff */
u8 had_frag; /* >= 1 fragments have been sent */
@@ -641,8 +642,9 @@ static long ppp_ioctl(struct file *file, unsigned int cmd,
unsigned long arg)
}
if (pf->kind == CHANNEL) {
- struct channel *pch;
+ struct channel *pch, *pchb;
struct ppp_channel *chan;
+ struct ppp_net *pn;
pch = PF_TO_CHANNEL(pf);
@@ -657,6 +659,24 @@ static long ppp_ioctl(struct file *file, unsigned int cmd,
unsigned long arg)
err = ppp_disconnect_channel(pch);
break;
+ case PPPIOCBRIDGECHAN:
+ if (get_user(unit, p))
+ break;
+ err = -ENXIO;
+ if (pch->bridge) {
+ err = -EALREADY;
+ break;
+ }
+ pn = ppp_pernet(current->nsproxy->net_ns);
+ spin_lock_bh(&pn->all_channels_lock);
+ pchb = ppp_find_channel(pn, unit);
+ if (pchb) {
+ refcount_inc(&pchb->file.refcnt);
+ pch->bridge = pchb;
+ err = 0;
+ }
+ spin_unlock_bh(&pn->all_channels_lock);
+ break;
default:
down_read(&pch->chan_sem);
chan = pch->chan;
@@ -2100,6 +2120,12 @@ ppp_input(struct ppp_channel *chan, struct sk_buff *skb)
return;
}
+ if (pch->bridge) {
+ skb_queue_tail(&pch->bridge->file.xq, skb);
+ ppp_channel_push(pch->bridge);
+ return;
+ }
+
read_lock_bh(&pch->upl);
if (!ppp_decompress_proto(skb)) {
kfree_skb(skb);
@@ -2791,6 +2817,13 @@ ppp_unregister_channel(struct ppp_channel *chan)
up_write(&pch->chan_sem);
ppp_disconnect_channel(pch);
+ /* Drop our reference on a bridged channel, if any */
+ if (pch->bridge) {
+ if (refcount_dec_and_test(&pch->bridge->file.refcnt))
+ ppp_destroy_channel(pch->bridge);
+ pch->bridge = NULL;
+ }
+
pn = ppp_pernet(pch->chan_net);
spin_lock_bh(&pn->all_channels_lock);
list_del(&pch->list);
diff --git a/include/uapi/linux/ppp-ioctl.h b/include/uapi/linux/ppp-ioctl.h
index 7bd2a5a75348..4b97ab519c19 100644
--- a/include/uapi/linux/ppp-ioctl.h
+++ b/include/uapi/linux/ppp-ioctl.h
@@ -115,6 +115,7 @@ struct pppol2tp_ioc_stats {
#define PPPIOCATTCHAN _IOW('t', 56, int) /* attach to ppp channel */
#define PPPIOCGCHAN _IOR('t', 55, int) /* get ppp channel number */
#define PPPIOCGL2TPSTATS _IOR('t', 54, struct pppol2tp_ioc_stats)
+#define PPPIOCBRIDGECHAN _IOW('t', 53, int) /* bridge one channel to
another */
#define SIOCGPPPSTATS (SIOCDEVPRIVATE + 0)
#define SIOCGPPPVER (SIOCDEVPRIVATE + 1) /* NEVER change this!! */
--
2.17.1
