netdev - [PATCH net-next 4/4] 6lowpan: len field is not stored and accessed properly

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Date:	Mon, 11 Jun 2012 00:40:25 -0400
From:	Tony Cheneau <tony.cheneauh@...esiak.org>
To:	netdev@...r.kernel.org, linux-zigbee-devel@...ts.sourceforge.net
Cc:	alex.bluesman.smirnov@...il.com
Subject: [PATCH net-next 4/4] 6lowpan: len field is not stored and accessed
 properly

Lenght field should be encoded (and accessed) the other way around.
As it is currently written, it could lead to interroperability issues.

Also, I rewrote the code so that iphc0 argument of
lowpan_alloc_new_frame could be removed.
---
 net/ieee802154/6lowpan.c |   20 ++++++++++++--------
 1 files changed, 12 insertions(+), 8 deletions(-)

diff --git a/net/ieee802154/6lowpan.c b/net/ieee802154/6lowpan.c
index af2f12e..b400156 100644
--- a/net/ieee802154/6lowpan.c
+++ b/net/ieee802154/6lowpan.c
@@ -654,7 +654,7 @@ static void lowpan_fragment_timer_expired(unsigned
long entry_addr) }
 
 static struct lowpan_fragment *
-lowpan_alloc_new_frame(struct sk_buff *skb, u8 iphc0, u8 len, u16 tag)
+lowpan_alloc_new_frame(struct sk_buff *skb, u16 len, u16 tag)
 {
 	struct lowpan_fragment *frame;
 
@@ -665,7 +665,7 @@ lowpan_alloc_new_frame(struct sk_buff *skb, u8
iphc0, u8 len, u16 tag) 
 	INIT_LIST_HEAD(&frame->list);
 
-	frame->length = (iphc0 & 7) | (len << 3);
+	frame->length = len;
 	frame->tag = tag;
 
 	/* allocate buffer for frame assembling */
@@ -721,13 +721,17 @@ lowpan_process_data(struct sk_buff *skb)
 	case LOWPAN_DISPATCH_FRAGN:
 	{
 		struct lowpan_fragment *frame;
-		u8 len, offset;
-		u16 tag;
+		/* slen stores the rightmost 8 bits of the 11 bits
length */
+		u8 slen, offset;
+		u16 len, tag;
 		bool found = false;
 
-		len = lowpan_fetch_skb_u8(skb); /* frame length */
+		slen = lowpan_fetch_skb_u8(skb); /* frame length */
 		tag = lowpan_fetch_skb_u16(skb);
 
+		/* adds the 3 MSB to the 8 LSB to retrieve the 11 bits
length */
+		len = ((iphc0 & 7) << 8) | slen;
+
 		/*
 		 * check if frame assembling with the same tag is
 		 * already in progress
@@ -742,7 +746,7 @@ lowpan_process_data(struct sk_buff *skb)
 
 		/* alloc new frame structure */
 		if (!found) {
-			frame = lowpan_alloc_new_frame(skb, iphc0,
len, tag);
+			frame = lowpan_alloc_new_frame(skb, len, tag);
 			if (!frame)
 				goto unlock_and_drop;
 		}
@@ -1000,8 +1004,8 @@ lowpan_skb_fragmentation(struct sk_buff *skb)
 	tag = fragment_tag++;
 
 	/* first fragment header */
-	head[0] = LOWPAN_DISPATCH_FRAG1 | (payload_length & 0x7);
-	head[1] = (payload_length >> 3) & 0xff;
+	head[0] = LOWPAN_DISPATCH_FRAG1 | ((payload_length >> 8) &
0x7);
+	head[1] = payload_length & 0xff;
 	head[2] = tag >> 8;
 	head[3] = tag & 0xff;
 
-- 
1.7.3.4

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