[3.13.y-ckt stable] Patch "batman-adv: Calculate extra tail size based on queued fragments" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    batman-adv: Calculate extra tail size based on queued fragments

to the linux-3.13.y-queue branch of the 3.13.y-ckt extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.13.y-queue

This patch is scheduled to be released in version 3.13.11-ckt14.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.13.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

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>From e6e75eaa937c7b55eeb7b689991883c5b2efdbdf Mon Sep 17 00:00:00 2001
From: Sven Eckelmann <sven at narfation.org>
Date: Sat, 20 Dec 2014 13:48:55 +0100
Subject: batman-adv: Calculate extra tail size based on queued fragments
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

commit 5b6698b0e4a37053de35cc24ee695b98a7eb712b upstream.

The fragmentation code was replaced in 610bfc6bc99bc83680d190ebc69359a05fc7f605
("batman-adv: Receive fragmented packets and merge"). The new code provided a
mostly unused parameter skb for the merging function. It is used inside the
function to calculate the additionally needed skb tailroom. But instead of
increasing its own tailroom, it is only increasing the tailroom of the first
queued skb. This is not correct in some situations because the first queued
entry can be a different one than the parameter.

An observed problem was:

1. packet with size 104, total_size 1464, fragno 1 was received
   - packet is queued
2. packet with size 1400, total_size 1464, fragno 0 was received
   - packet is queued at the end of the list
3. enough data was received and can be given to the merge function
   (1464 == (1400 - 20) + (104 - 20))
   - merge functions gets 1400 byte large packet as skb argument
4. merge function gets first entry in queue (104 byte)
   - stored as skb_out
5. merge function calculates the required extra tail as total_size - skb->len
   - pskb_expand_head tail of skb_out with 64 bytes
6. merge function tries to squeeze the extra 1380 bytes from the second queued
   skb (1400 byte aka skb parameter) in the 64 extra tail bytes of skb_out

Instead calculate the extra required tail bytes for skb_out also using skb_out
instead of using the parameter skb. The skb parameter is only used to get the
total_size from the last received packet. This is also the total_size used to
decide that all fragments were received.

Reported-by: Philipp Psurek <philipp.psurek at gmail.com>
Signed-off-by: Sven Eckelmann <sven at narfation.org>
Acked-by: Martin Hundebøll <martin at hundeboll.net>
Signed-off-by: David S. Miller <davem at davemloft.net>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 net/batman-adv/fragmentation.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/batman-adv/fragmentation.c b/net/batman-adv/fragmentation.c
index 8a1d4b54..b3c4223 100644
--- a/net/batman-adv/fragmentation.c
+++ b/net/batman-adv/fragmentation.c
@@ -253,7 +253,7 @@ batadv_frag_merge_packets(struct hlist_head *chain, struct sk_buff *skb)
 	kfree(entry);

 	/* Make room for the rest of the fragments. */
-	if (pskb_expand_head(skb_out, 0, size - skb->len, GFP_ATOMIC) < 0) {
+	if (pskb_expand_head(skb_out, 0, size - skb_out->len, GFP_ATOMIC) < 0) {
 		kfree_skb(skb_out);
 		skb_out = NULL;
 		goto free;
--
1.9.1