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-rw-r--r--drivers/net/ppp_generic.c7
1 files changed, 6 insertions, 1 deletions
diff --git a/drivers/net/ppp_generic.c b/drivers/net/ppp_generic.c
index 10e5d98..edfa15d 100644
--- a/drivers/net/ppp_generic.c
+++ b/drivers/net/ppp_generic.c
@@ -1465,7 +1465,12 @@ static int ppp_mp_explode(struct ppp *ppp, struct sk_buff *skb)
continue;
}
- mtu = pch->chan->mtu - hdrlen;
+ /*
+ * hdrlen includes the 2-byte PPP protocol field, but the
+ * MTU counts only the payload excluding the protocol field.
+ * (RFC1661 Section 2)
+ */
+ mtu = pch->chan->mtu - (hdrlen - 2);
if (mtu < 4)
mtu = 4;
if (flen > mtu)

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