net: Fix truesize accounting in skb_gro_receive()

GRO is very optimistic in skb truesize estimates, only taking into
account the used part of fragments.

Be conservative, and use more precise computation, so that bloated GRO
skbs can be collapsed eventually.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Alexander Duyck <alexander.h.duyck@intel.com>
Cc: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Acked-by: Alexander Duyck <alexander.h.duyck@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 9e8caa0..e1f8bba 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -2871,6 +2871,7 @@
 	unsigned int len = skb_gro_len(skb);
 	unsigned int offset = skb_gro_offset(skb);
 	unsigned int headlen = skb_headlen(skb);
+	unsigned int delta_truesize;
 
 	if (p->len + len >= 65536)
 		return -E2BIG;
@@ -2900,11 +2901,14 @@
 		frag->page_offset += offset;
 		skb_frag_size_sub(frag, offset);
 
+		/* all fragments truesize : remove (head size + sk_buff) */
+		delta_truesize = skb->truesize - SKB_TRUESIZE(skb_end_pointer(skb) - skb->head);
+
 		skb->truesize -= skb->data_len;
 		skb->len -= skb->data_len;
 		skb->data_len = 0;
 
-		NAPI_GRO_CB(skb)->free = 1;
+		NAPI_GRO_CB(skb)->free = NAPI_GRO_FREE;
 		goto done;
 	} else if (skb->head_frag) {
 		int nr_frags = pinfo->nr_frags;
@@ -2929,6 +2933,7 @@
 		memcpy(frag + 1, skbinfo->frags, sizeof(*frag) * skbinfo->nr_frags);
 		/* We dont need to clear skbinfo->nr_frags here */
 
+		delta_truesize = skb->truesize - SKB_DATA_ALIGN(sizeof(struct sk_buff));
 		NAPI_GRO_CB(skb)->free = NAPI_GRO_FREE_STOLEN_HEAD;
 		goto done;
 	} else if (skb_gro_len(p) != pinfo->gso_size)
@@ -2971,7 +2976,7 @@
 	p = nskb;
 
 merge:
-	p->truesize += skb->truesize - len;
+	delta_truesize = skb->truesize;
 	if (offset > headlen) {
 		unsigned int eat = offset - headlen;
 
@@ -2991,7 +2996,7 @@
 done:
 	NAPI_GRO_CB(p)->count++;
 	p->data_len += len;
-	p->truesize += len;
+	p->truesize += delta_truesize;
 	p->len += len;
 
 	NAPI_GRO_CB(skb)->same_flow = 1;