[PATCH 3.13 057/212] net: gro: make sure skb->cb[] initial content has not to be zero

[Kamal Mostafa]

3.13.11.4 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Eric Dumazet <edumazet at google.com>

[ 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