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

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Date:	Fri, 16 May 2014 11:34:37 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Timo Teras <timo.teras@....fi>
Cc:	Eric Dumazet <edumazet@...gle.com>, netdev@...r.kernel.org,
	Herbert Xu <herbert@...dor.apana.org.au>
Subject: [PATCH] net: gro: make sure skb->cb[] initial content has not to be
 zero

From: Eric Dumazet <edumazet@...gle.com>

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@....fi>
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
Please Timo test this patch so that we confirm it fixes the bug for you.

 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 6da649bde4f7..ed928e846559 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -3951,6 +3951,7 @@ static enum gro_result dev_gro_receive(struct napi_struct *napi, struct sk_buff
 	}
 	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 1b62343f5837..8383b2bddeb9 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -3076,7 +3076,7 @@ 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) {
@@ -3192,7 +3192,7 @@ 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;


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