netdev - Re: [PATCH RFC] r8169: straighten out overlength frame detection (v3)

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20100105135732.GA24245@hmsreliant.think-freely.org>
Date:	Tue, 5 Jan 2010 08:57:32 -0500
From:	Neil Horman <nhorman@...driver.com>
To:	netdev@...r.kernel.org
Cc:	davem@...emloft.net, nhorman@...driver.com, romieu@...zoreil.com
Subject: Re: [PATCH RFC] r8169: straighten out overlength frame detection (v3)

Ok, third times the charm.  Its been noted that both apporaches to fixing this
bug are going to have major performance impacts, which is bad.  Unless we can
get a list of affected hardware to restrict the fix to certain NICS, I don't see
how we can get around that.   I have come up with this patch however, which I
think at least partially addresses the performance concerns.

        A while back Eric submitted a patch for r8169 in which the proper
allocated frame size was written to RXMaxSize to prevent the NIC from dmaing too
much data.  This was done in commit fdd7b4c3302c93f6833e338903ea77245eb510b4.  A
long time prior to that however, Francois posted
126fa4b9ca5d9d7cb7d46f779ad3bd3631ca387c, which expiclitly disabled the MaxSize
setting due to the fact that the hardware behaved in odd ways when overlong
frames were received on NIC's supported by this driver.  This was mentioned in a
security conference recently:
http://events.ccc.de/congress/2009/Fahrplan//events/3596.en.html

It seems that if we can't enable frame size filtering, then, as Eric correctly
noticed, we can find ourselves DMA-ing too much data to a buffer, causing
corruption.  As a result is seems that we are forced to allocate a frame which
is ready to handle a maximally sized receive.

This obviously has performance issues with it, so to mitigate that issue, this
patch does two things:

1) Raises the copybreak value to the frame allocation size, which should force
appropriately sized packets to get allocated on rx, rather than a full new 16k
buffer.

2) This patch only disables frame filtering initially (i.e., during the NIC
open), changing the MTU results in ring buffer allocation of a size in relation
to the new mtu (along with a warning indicating that this is dangerous).

Because of item (2), individuals who can't cope with the performance hit (or can
otherwise filter frames to prevent the bug), or who have hardware they are sure
is unaffected by this issue, can manually lower the copybreak and reset the mtu
such that performance is restored easily.

Signed-off-by: Neil Horman <nhorman@...hat.com>



 r8169.c |   29 ++++++++++++++++++++++++-----
 1 file changed, 24 insertions(+), 5 deletions(-)


diff --git a/drivers/net/r8169.c b/drivers/net/r8169.c
index c403ce0..9aac49c 100644
--- a/drivers/net/r8169.c
+++ b/drivers/net/r8169.c
@@ -186,7 +186,12 @@ static struct pci_device_id rtl8169_pci_tbl[] = {
 
 MODULE_DEVICE_TABLE(pci, rtl8169_pci_tbl);
 
-static int rx_copybreak = 200;
+/*
+ * we set our copybreak very high so that we don't have
+ * to allocate 16k frames all the time (see note in
+ * rtl8169_open()
+ */ 
+static int rx_copybreak = 16383;
 static int use_dac;
 static struct {
 	u32 msg_enable;
@@ -3240,9 +3245,13 @@ static void __devexit rtl8169_remove_one(struct pci_dev *pdev)
 }
 
 static void rtl8169_set_rxbufsize(struct rtl8169_private *tp,
-				  struct net_device *dev)
+				  unsigned int mtu)
 {
-	unsigned int max_frame = dev->mtu + VLAN_ETH_HLEN + ETH_FCS_LEN;
+	unsigned int max_frame = mtu + VLAN_ETH_HLEN + ETH_FCS_LEN;
+
+	if (max_frame != 16383)
+		printk(KERN_WARNING "WARNING! Changing of MTU on this NIC"
+			"May lead to frame reception errors!\n");
 
 	tp->rx_buf_sz = (max_frame > RX_BUF_SIZE) ? max_frame : RX_BUF_SIZE;
 }
@@ -3254,7 +3263,17 @@ static int rtl8169_open(struct net_device *dev)
 	int retval = -ENOMEM;
 
 
-	rtl8169_set_rxbufsize(tp, dev);
+	/*
+	 * Note that we use a magic value here, its wierd I know
+	 * its done because, some subset of rtl8169 hardware suffers from
+	 * a problem in which frames received that are longer than 
+	 * the size set in RxMaxSize register return garbage sizes
+	 * when received.  To avoid this we need to turn off filtering, 
+	 * which is done by setting a value of 16383 in the RxMaxSize register
+	 * and allocating 16k frames to handle the largest possible rx value
+	 * thats what the magic math below does.
+	 */
+	rtl8169_set_rxbufsize(tp, 16383 - VLAN_ETH_HLEN - ETH_FCS_LEN);
 
 	/*
 	 * Rx and Tx desscriptors needs 256 bytes alignment.
@@ -3907,7 +3926,7 @@ static int rtl8169_change_mtu(struct net_device *dev, int new_mtu)
 
 	rtl8169_down(dev);
 
-	rtl8169_set_rxbufsize(tp, dev);
+	rtl8169_set_rxbufsize(tp, dev->mtu);
 
 	ret = rtl8169_init_ring(dev);
 	if (ret < 0)
--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html