linux-kernel - [09/45] r8169: Fix receive buffer length when MTU is between 1515 and 1536

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Message-Id: <20100330224944.777509723@linux.site>
Date:	Tue, 30 Mar 2010 15:48:29 -0700
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org
Cc:	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Raimonds Cicans <ray@...llo.lv>,
	"David S. Miller" <davem@...emloft.net>,
	Jean Delvare <khali@...ux-fr.org>,
	Greg Kroah-Hartman <gregkh@...e.de>
Subject: [09/45] r8169: Fix receive buffer length when MTU is between 1515 and 1536

2.6.27-stable review patch.  If anyone has any objections, please let us know.

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

From: Raimonds Cicans <ray@...llo.lv>

commit 8812304cf1110ae16b0778680f6022216cf4716a upstream.

In r8169 driver MTU is used to calculate receive buffer size.
Receive buffer size is used to configure hardware incoming packet filter.

For jumbo frames:
Receive buffer size = Max frame size = MTU + 14 (ethernet header) + 4
(vlan header) + 4 (ethernet checksum) = MTU + 22

Bug:
driver for all MTU up to 1536 use receive buffer size 1536

As you can see from formula, this mean all IP packets > 1536 - 22
(for vlan tagged, 1536 - 18 for not tagged) are dropped by hardware
filter.

Example:

host_good>  ifconfig eth0 mtu 1536
host_r8169> ifconfig eth0 mtu 1536
host_good>  ping host_r8169
Ok
host_good>  ping -s 1500 host_r8169
Fail
host_good>  ifconfig eth0 mtu 7000
host_r8169> ifconfig eth0 mtu 7000
host_good>  ping -s 1500 host_r8169
Ok

Bonus: got rid of magic number 8

Signed-off-by: Raimonds Cicans <ray@...llo.lv>
Signed-off-by: David S. Miller <davem@...emloft.net>
Cc: Jean Delvare <khali@...ux-fr.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

---
 drivers/net/r8169.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/drivers/net/r8169.c
+++ b/drivers/net/r8169.c
@@ -1842,9 +1842,9 @@ static void __devexit rtl8169_remove_one
 static void rtl8169_set_rxbufsize(struct rtl8169_private *tp,
 				  struct net_device *dev)
 {
-	unsigned int mtu = dev->mtu;
+	unsigned int max_frame = dev->mtu + VLAN_ETH_HLEN + ETH_FCS_LEN;
 
-	tp->rx_buf_sz = (mtu > RX_BUF_SIZE) ? mtu + ETH_HLEN + 8 : RX_BUF_SIZE;
+	tp->rx_buf_sz = (max_frame > RX_BUF_SIZE) ? max_frame : RX_BUF_SIZE;
 }
 
 static int rtl8169_open(struct net_device *dev)


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