gro: Fix potential use after free

The initial skb may have been freed after napi_gro_complete in
napi_gro_receive if it was merged into an existing packet.  Thus
we cannot check same_flow (which indicates whether it was merged)
after calling napi_gro_complete.

This patch fixes this by saving the same_flow status before the
call to napi_gro_complete.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 4 insertions, 1 deletions

diff --git a/net/core/dev.c b/net/core/dev.c
index 536a8ac189c8..303e984ee6a6 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -2390,6 +2390,7 @@ int napi_gro_receive(struct napi_struct *napi, struct sk_buff *skb)
         __be16 type = skb->protocol;
         struct list_head *head = &ptype_base[ntohs(type) & PTYPE_HASH_MASK];
         int count = 0;
+        int same_flow;
         int mac_len;
 
         if (!(skb->dev->features & NETIF_F_GRO))
@@ -2425,6 +2426,8 @@ int napi_gro_receive(struct napi_struct *napi, struct sk_buff *skb)
         if (&ptype->list == head)
                 goto normal;
 
+        same_flow = NAPI_GRO_CB(skb)->same_flow;
+
         if (pp) {
                 struct sk_buff *nskb = *pp;
 
@@ -2434,7 +2437,7 @@ int napi_gro_receive(struct napi_struct *napi, struct sk_buff *skb)
                 count--;
         }
 
-        if (NAPI_GRO_CB(skb)->same_flow)
+        if (same_flow)
                 goto ok;
 
         if (NAPI_GRO_CB(skb)->flush || count >= MAX_GRO_SKBS) {