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Date:	Sun, 13 Apr 2014 23:57:40 +0100
From:	Ben Hutchings <>
To:	David Miller <>
Cc:, "Michael S. Tsirkin" <>,
	Herbert Xu <>,
	netdev <>
Subject: [PATCH 3.2-3.12] skbuff: skb_segment: orphan frags before copying

From: "Michael S. Tsirkin" <>

commit 1fd819ecb90cc9b822cd84d3056ddba315d3340f upstream.

skb_segment copies frags around, so we need
to copy them carefully to avoid accessing
user memory after reporting completion to userspace
through a callback.

skb_segment doesn't normally happen on datapath:
TSO needs to be disabled - so disabling zero copy
in this case does not look like a big deal.

Signed-off-by: Michael S. Tsirkin <>
Acked-by: Herbert Xu <>
Signed-off-by: David S. Miller <>
[bwh: Backported to 3.2.  As skb_segment() only supports page-frags *or* a
 frag list, there is no need for the additional frag_skb pointer or the
 preparatory renaming.]
Signed-off-by: Ben Hutchings <>
For branches older than 3.6, commit a353e0ce0fd4 ('skbuff: add an api to
orphan frags') is needed before this.  This is untested and I would
appreciate a review.

--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -2699,6 +2699,9 @@ struct sk_buff *skb_segment(struct sk_bu
 						 skb_put(nskb, hsize), hsize);
 		while (pos < offset + len && i < nfrags) {
+			if (unlikely(skb_orphan_frags(skb, GFP_ATOMIC)))
+				goto err;
 			*frag = skb_shinfo(skb)->frags[i];
 			size = skb_frag_size(frag);

Ben Hutchings
I haven't lost my mind; it's backed up on tape somewhere.

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