[3.13.y.z extended stable] Patch "net: gro: make sure skb->cb[] initial content has not to be zero" has been added to staging queue

[Kamal Mostafa]

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

    net: gro: make sure skb->cb[] initial content has not to be zero

to the linux-3.13.y-queue branch of the 3.13.y.z 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 3.13.11.4.

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.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

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>From ca6b3a15bd1b652ca5fa02fa44315d01c9deffb4 Mon Sep 17 00:00:00 2001
From: Eric Dumazet <edumazet at google.com>
Date: Fri, 16 May 2014 11:34:37 -0700
Subject: net: gro: make sure skb->cb[] initial content has not to be zero
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

[ Upstream commit 29e98242783ed3ba569797846a606ba66f781625 ]

Starting from linux-3.13, GRO attempts to build full size skbs.

Problem is the commit assumed one particular field in skb->cb[]
was clean, but it is not the case on some stacked devices.

Timo reported a crash in case traffic is decrypted before
reaching a GRE device.

Fix this by initializing NAPI_GRO_CB(skb)->last at the right place,
this also removes one conditional.

Thanks a lot to Timo for providing full reports and bisecting this.

Fixes: 8a29111c7ca6 ("net: gro: allow to build full sized skb")
Bisected-by: Timo Teras <timo.teras at iki.fi>
Signed-off-by: Eric Dumazet <edumazet at google.com>
Tested-by: Timo Teräs <timo.teras at iki.fi>
Signed-off-by: David S. Miller <davem at davemloft.net>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 net/core/dev.c    | 1 +
 net/core/skbuff.c | 4 ++--
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index 233d1c4..4c0ff6f 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -3882,6 +3882,7 @@ static enum gro_result dev_gro_receive(struct napi_struct *napi, struct sk_buff
 	napi->gro_count++;
 	NAPI_GRO_CB(skb)->count = 1;
 	NAPI_GRO_CB(skb)->age = jiffies;
+	NAPI_GRO_CB(skb)->last = skb;
 	skb_shinfo(skb)->gso_size = skb_gro_len(skb);
 	skb->next = napi->gro_list;
 	napi->gro_list = skb;
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index bdd6955..f45d60d 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -2980,7 +2980,7 @@ int skb_gro_receive(struct sk_buff **head, struct sk_buff *skb)
 	if (unlikely(p->len + len >= 65536))
 		return -E2BIG;

-	lp = NAPI_GRO_CB(p)->last ?: p;
+	lp = NAPI_GRO_CB(p)->last;
 	pinfo = skb_shinfo(lp);

 	if (headlen <= offset) {
@@ -3096,7 +3096,7 @@ merge:

 	__skb_pull(skb, offset);

-	if (!NAPI_GRO_CB(p)->last)
+	if (NAPI_GRO_CB(p)->last == p)
 		skb_shinfo(p)->frag_list = skb;
 	else
 		NAPI_GRO_CB(p)->last->next = skb;
--
1.9.1