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

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

From: Eric Dumazet <[email protected]>

[ 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 <[email protected]>
Signed-off-by: Eric Dumazet <[email protected]>
Tested-by: Timo Ter�s <[email protected]>
Signed-off-by: David S. Miller <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
 net/core/dev.c    |    1 +
 net/core/skbuff.c |    4 ++--
 2 files changed, 3 insertions(+), 2 deletions(-)

--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -3944,6 +3944,7 @@ static enum gro_result dev_gro_receive(s
        }
        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;
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -3076,7 +3076,7 @@ int skb_gro_receive(struct sk_buff **hea
        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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