[PATCH] Fixed zero copy GSO without orphaning the fragments

[Igor Royzis <igorr@swortex.com>]

Fix accessing GSO fragments memory (and a possible corruption therefore) after
reporting completion in a zero copy callback. The previous fix in the commit 1fd819ec
orphaned frags which eliminates zero copy advantages. The fix makes the completion
called after all the fragments were processed avoiding unnecessary orphaning/copying
from userspace.

The GSO fragments corruption issue was observed in a typical QEMU/KVM VM setup that
hosts a Windows guest (since QEMU virtio-net Windows driver doesn't support GRO).
The fix has been verified by running the HCK OffloadLSO test.

Signed-off-by: Igor Royzis <igorr@swortex.com>
Signed-off-by: Anton Nayshtut <anton@swortex.com>
---
 include/linux/skbuff.h |    1 +
 net/core/skbuff.c      |   18 +++++++++++++-----
 2 files changed, 14 insertions(+), 5 deletions(-)

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 08074a8..8c49edc 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -287,6 +287,7 @@ struct skb_shared_info {
 	struct sk_buff	*frag_list;
 	struct skb_shared_hwtstamps hwtstamps;
 	__be32          ip6_frag_id;
+	struct sk_buff  *zcopy_src;
 
 	/*
 	 * Warning : all fields before dataref are cleared in __alloc_skb()
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 1b62343..6fa6342 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -610,14 +610,18 @@ EXPORT_SYMBOL(__kfree_skb);
  */
 void kfree_skb(struct sk_buff *skb)
 {
+	struct sk_buff *zcopy_src;
 	if (unlikely(!skb))
 		return;
 	if (likely(atomic_read(&skb->users) == 1))
 		smp_rmb();
 	else if (likely(!atomic_dec_and_test(&skb->users)))
 		return;
+	zcopy_src = skb_shinfo(skb)->zcopy_src;
 	trace_kfree_skb(skb, __builtin_return_address(0));
 	__kfree_skb(skb);
+	if (unlikely(zcopy_src))
+		kfree_skb(zcopy_src);
 }
 EXPORT_SYMBOL(kfree_skb);
 
@@ -662,14 +666,18 @@ EXPORT_SYMBOL(skb_tx_error);
  */
 void consume_skb(struct sk_buff *skb)
 {
+	struct sk_buff *zcopy_src;
 	if (unlikely(!skb))
 		return;
 	if (likely(atomic_read(&skb->users) == 1))
 		smp_rmb();
 	else if (likely(!atomic_dec_and_test(&skb->users)))
 		return;
+	zcopy_src = skb_shinfo(skb)->zcopy_src;
 	trace_consume_skb(skb);
 	__kfree_skb(skb);
+	if (unlikely(zcopy_src))
+		consume_skb(zcopy_src);
 }
 EXPORT_SYMBOL(consume_skb);
 
@@ -2867,7 +2875,6 @@ struct sk_buff *skb_segment(struct sk_buff *head_skb,
 	skb_frag_t *frag = skb_shinfo(head_skb)->frags;
 	unsigned int mss = skb_shinfo(head_skb)->gso_size;
 	unsigned int doffset = head_skb->data - skb_mac_header(head_skb);
-	struct sk_buff *frag_skb = head_skb;
 	unsigned int offset = doffset;
 	unsigned int tnl_hlen = skb_tnl_header_len(head_skb);
 	unsigned int headroom;
@@ -2913,7 +2920,6 @@ struct sk_buff *skb_segment(struct sk_buff *head_skb,
 			i = 0;
 			nfrags = skb_shinfo(list_skb)->nr_frags;
 			frag = skb_shinfo(list_skb)->frags;
-			frag_skb = list_skb;
 			pos += skb_headlen(list_skb);
 
 			while (pos < offset + len) {
@@ -2975,6 +2981,11 @@ struct sk_buff *skb_segment(struct sk_buff *head_skb,
 						 nskb->data - tnl_hlen,
 						 doffset + tnl_hlen);
 
+		if (skb_shinfo(head_skb)->tx_flags & SKBTX_DEV_ZEROCOPY) {
+			skb_shinfo(nskb)->zcopy_src = head_skb;
+			atomic_inc(&head_skb->users);
+		}
+
 		if (nskb->len == len + doffset)
 			goto perform_csum_check;
 
@@ -3001,7 +3012,6 @@ struct sk_buff *skb_segment(struct sk_buff *head_skb,
 				i = 0;
 				nfrags = skb_shinfo(list_skb)->nr_frags;
 				frag = skb_shinfo(list_skb)->frags;
-				frag_skb = list_skb;
 
 				BUG_ON(!nfrags);
 
@@ -3016,8 +3026,6 @@ struct sk_buff *skb_segment(struct sk_buff *head_skb,
 				goto err;
 			}
 
-			if (unlikely(skb_orphan_frags(frag_skb, GFP_ATOMIC)))
-				goto err;
 
 			*nskb_frag = *frag;
 			__skb_frag_ref(nskb_frag);
-- 
1.7.9.5