linux-kernel - [ 38/48] netpoll: fix netpoll_send

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Message-Id: <20120709143122.140128311@decadent.org.uk>
Date:	Mon, 09 Jul 2012 15:31:54 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
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 <edumazet@...gle.com>,
	Bogdan Hamciuc <bogdan.hamciuc@...escale.com>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	Neil Horman <nhorman@...driver.com>,
	Cong Wang <xiyou.wangcong@...il.com>,
	"David S. Miller" <davem@...emloft.net>
Subject: [ 38/48] netpoll: fix netpoll_send_udp() bugs

3.2-stable review patch.  If anyone has any objections, please let me know.

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

From: Eric Dumazet <edumazet@...gle.com>

[ Upstream commit 954fba0274058d27c7c07b5ea07c41b3b7477894 ]

Bogdan Hamciuc diagnosed and fixed following bug in netpoll_send_udp() :

"skb->len += len;" instead of "skb_put(skb, len);"

Meaning that _if_ a network driver needs to call skb_realloc_headroom(),
only packet headers would be copied, leaving garbage in the payload.

However the skb_realloc_headroom() must be avoided as much as possible
since it requires memory and netpoll tries hard to work even if memory
is exhausted (using a pool of preallocated skbs)

It appears netpoll_send_udp() reserved 16 bytes for the ethernet header,
which happens to work for typicall drivers but not all.

Right thing is to use LL_RESERVED_SPACE(dev)
(And also add dev->needed_tailroom of tailroom)

This patch combines both fixes.

Many thanks to Bogdan for raising this issue.

Reported-by: Bogdan Hamciuc <bogdan.hamciuc@...escale.com>
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Tested-by: Bogdan Hamciuc <bogdan.hamciuc@...escale.com>
Cc: Herbert Xu <herbert@...dor.apana.org.au>
Cc: Neil Horman <nhorman@...driver.com>
Reviewed-by: Neil Horman <nhorman@...driver.com>
Reviewed-by: Cong Wang <xiyou.wangcong@...il.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 net/core/netpoll.c |   11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/net/core/netpoll.c b/net/core/netpoll.c
index ab0633f..db4bb7a 100644
--- a/net/core/netpoll.c
+++ b/net/core/netpoll.c
@@ -351,22 +351,23 @@ EXPORT_SYMBOL(netpoll_send_skb_on_dev);
 
 void netpoll_send_udp(struct netpoll *np, const char *msg, int len)
 {
-	int total_len, eth_len, ip_len, udp_len;
+	int total_len, ip_len, udp_len;
 	struct sk_buff *skb;
 	struct udphdr *udph;
 	struct iphdr *iph;
 	struct ethhdr *eth;
 
 	udp_len = len + sizeof(*udph);
-	ip_len = eth_len = udp_len + sizeof(*iph);
-	total_len = eth_len + ETH_HLEN + NET_IP_ALIGN;
+	ip_len = udp_len + sizeof(*iph);
+	total_len = ip_len + LL_RESERVED_SPACE(np->dev);
 
-	skb = find_skb(np, total_len, total_len - len);
+	skb = find_skb(np, total_len + np->dev->needed_tailroom,
+		       total_len - len);
 	if (!skb)
 		return;
 
 	skb_copy_to_linear_data(skb, msg, len);
-	skb->len += len;
+	skb_put(skb, len);
 
 	skb_push(skb, sizeof(*udph));
 	skb_reset_transport_header(skb);


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