[PATCH net-next] 6lowpan_rtnl: fix fragmentation with two fragments

[PATCH net-next] 6lowpan_rtnl: fix fragmentation with two fragments

[Alexander Aring]

This patch fix the 6LoWPAN fragmentation for the case if we have exactly
two fragments. The problem is that the (skb_unprocessed >= frag_cap)
condition is always false on the second fragment after sending the first
fragment. A fragmentation with only one fragment doesn't make any sense.
The solution is that we use a do while loop here, that ensures we sending
always a minimum of two fragments if we need a fragmentation.

This issue was introduced by commit d4b2816d67d6e07b2f27037f282d8db03a5829d7
("6lowpan: fix fragmentation").

Signed-off-by: Alexander Aring <alex.aring-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
---
 net/ieee802154/6lowpan_rtnl.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/ieee802154/6lowpan_rtnl.c b/net/ieee802154/6lowpan_rtnl.c
index 1ae8a56..9d57026 100644
--- a/net/ieee802154/6lowpan_rtnl.c
+++ b/net/ieee802154/6lowpan_rtnl.c
@@ -312,7 +312,7 @@ lowpan_xmit_fragmented(struct sk_buff *skb, struct net_device *dev,
 	frag_hdr[0] |= LOWPAN_DISPATCH_FRAGN;
 	frag_cap = round_down(payload_cap - LOWPAN_FRAGN_HEAD_SIZE, 8);
 
-	while (skb_unprocessed >= frag_cap) {
+	do {
 		dgram_offset += frag_len;
 		skb_offset += frag_len;
 		skb_unprocessed -= frag_len;
@@ -328,7 +328,7 @@ lowpan_xmit_fragmented(struct sk_buff *skb, struct net_device *dev,
 				 __func__, frag_tag, skb_offset);
 			goto err;
 		}
-	}
+	} while (skb_unprocessed >= frag_cap);
 
 	consume_skb(skb);
 	return NET_XMIT_SUCCESS;
-- 
1.9.3


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Re: [PATCH net-next] 6lowpan_rtnl: fix fragmentation with two fragments

[Alexander Aring]

Hi,

please ignore this one, I also detected a off by one error on a corner
of a multiple fragment payload length if we have 3 fragments or above.

- Alex

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