netdev - Re: Bug in skb_segment: fskb->len != len

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Date:	Mon, 28 Oct 2013 18:15:08 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Christoph Paasch <christoph.paasch@...ouvain.be>
Cc:	Herbert Xu <herbert@...dor.apana.org.au>,
	netdev <netdev@...r.kernel.org>
Subject: Re: Bug in skb_segment: fskb->len != len

On Mon, 2013-10-28 at 06:21 -0700, Eric Dumazet wrote:

> But we also need to fix the skb_segment() bug anyway.

Hi Christoph

I cooked a minimal patch, could you please try it ?

I'll refactor skb_segment() to be smarter for the next release
(linux-3.14).

Thanks !

 net/core/skbuff.c |   15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 0ab32faa520f..771946487a8d 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -2761,7 +2761,7 @@ struct sk_buff *skb_segment(struct sk_buff *skb, netdev_features_t features)
 	unsigned int len;
 	__be16 proto;
 	bool csum;
-	int sg = !!(features & NETIF_F_SG);
+	bool sg = !!(features & NETIF_F_SG);
 	int nfrags = skb_shinfo(skb)->nr_frags;
 	int err = -ENOMEM;
 	int i = 0;
@@ -2793,7 +2793,11 @@ struct sk_buff *skb_segment(struct sk_buff *skb, netdev_features_t features)
 			hsize = len;
 
 		if (!hsize && i >= nfrags) {
-			BUG_ON(fskb->len != len);
+			if (fskb->len != len) {
+				hsize = len;
+				sg = false;
+				goto do_linear;
+			}
 
 			pos += len;
 			nskb = skb_clone(fskb, GFP_ATOMIC);
@@ -2812,6 +2816,7 @@ struct sk_buff *skb_segment(struct sk_buff *skb, netdev_features_t features)
 			skb_release_head_state(nskb);
 			__skb_push(nskb, doffset);
 		} else {
+do_linear:
 			nskb = __alloc_skb(hsize + doffset + headroom,
 					   GFP_ATOMIC, skb_alloc_rx_flag(skb),
 					   NUMA_NO_NODE);
@@ -2838,9 +2843,6 @@ struct sk_buff *skb_segment(struct sk_buff *skb, netdev_features_t features)
 						 nskb->data - tnl_hlen,
 						 doffset + tnl_hlen);
 
-		if (fskb != skb_shinfo(skb)->frag_list)
-			goto perform_csum_check;
-
 		if (!sg) {
 			nskb->ip_summed = CHECKSUM_NONE;
 			nskb->csum = skb_copy_and_csum_bits(skb, offset,
@@ -2849,6 +2851,9 @@ struct sk_buff *skb_segment(struct sk_buff *skb, netdev_features_t features)
 			continue;
 		}
 
+		if (fskb != skb_shinfo(skb)->frag_list)
+			goto perform_csum_check;
+
 		frag = skb_shinfo(nskb)->frags;
 
 		skb_copy_from_linear_data_offset(skb, offset,


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