linux-kernel - [087/101] gro: fix different skb headrooms

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Message-Id: <20111102222747.755827142@clark.kroah.org>
Date:	Wed, 02 Nov 2011 15:27:11 -0700
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	alan@...rguk.ukuu.org.uk, Eric Dumazet <eric.dumazet@...il.com>,
	Jarek Poplawski <jarkao2@...il.com>,
	Ben Hutchings <bhutchings@...arflare.com>,
	"David S. Miller" <davem@...emloft.net>
Subject: [087/101] gro: fix different skb headrooms

2.6.33-longterm review patch.  If anyone has any objections, please let us know.

------------------

From: Eric Dumazet <eric.dumazet@...il.com>

commit 3d3be4333fdf6faa080947b331a6a19bce1a4f57 upstream.

Packets entering GRO might have different headrooms, even for a given
flow (because of implementation details in drivers, like copybreak).
We cant force drivers to deliver packets with a fixed headroom.

1) fix skb_segment()

skb_segment() makes the false assumption headrooms of fragments are same
than the head. When CHECKSUM_PARTIAL is used, this can give csum_start
errors, and crash later in skb_copy_and_csum_dev()

2) allocate a minimal skb for head of frag_list

skb_gro_receive() uses netdev_alloc_skb(headroom + skb_gro_offset(p)) to
allocate a fresh skb. This adds NET_SKB_PAD to a padding already
provided by netdevice, depending on various things, like copybreak.

Use alloc_skb() to allocate an exact padding, to reduce cache line
needs:
NET_SKB_PAD + NET_IP_ALIGN

bugzilla : https://bugzilla.kernel.org/show_bug.cgi?id=16626

Many thanks to Plamen Petrov, testing many debugging patches !
With help of Jarek Poplawski.

Reported-by: Plamen Petrov <pvp-lsts@...uni-ruse.bg>
Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
CC: Jarek Poplawski <jarkao2@...il.com>
Cc: Ben Hutchings <bhutchings@...arflare.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

---
 net/core/skbuff.c |    8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -2578,6 +2578,10 @@ struct sk_buff *skb_segment(struct sk_bu
 		__copy_skb_header(nskb, skb);
 		nskb->mac_len = skb->mac_len;

+		/* nskb and skb might have different headroom */
+		if (nskb->ip_summed == CHECKSUM_PARTIAL)
+			nskb->csum_start += skb_headroom(nskb) - headroom;
+
 		skb_reset_mac_header(nskb);
 		skb_set_network_header(nskb, skb->mac_len);
 		nskb->transport_header = (nskb->network_header +
@@ -2707,8 +2711,8 @@ int skb_gro_receive(struct sk_buff **hea
 	} else if (skb_gro_len(p) != pinfo->gso_size)
 		return -E2BIG;

-	headroom = skb_headroom(p);
-	nskb = netdev_alloc_skb(p->dev, headroom + skb_gro_offset(p));
+	headroom = NET_SKB_PAD + NET_IP_ALIGN;
+	nskb = alloc_skb(headroom + skb_gro_offset(p), GFP_ATOMIC);
 	if (unlikely(!nskb))
 		return -ENOMEM;

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