netdev - RE: NULL Pointer Deference: NFS & Telnet

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Date:	Wed, 26 May 2010 22:48:53 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	"Arce, Abraham" <x0066660@...com>
Cc:	David Miller <davem@...emloft.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-nfs@...r.kernel.org" <linux-nfs@...r.kernel.org>,
	"linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>,
	"tony@...mide.com" <tony@...mide.com>,
	"Shilimkar, Santosh" <santosh.shilimkar@...com>,
	"Ha, Tristram" <Tristram.Ha@...rel.com>
Subject: RE: NULL Pointer Deference: NFS & Telnet

Le mercredi 26 mai 2010 à 15:19 -0500, Arce, Abraham a écrit :

> By increasing the allocation length of our rx skbuff the corruption issue is fixed... I have increased it by 2... Were we writing outside our boundaries of skb data?
> 
> Please let me know about this approach...
> 
> diff --git a/drivers/net/ks8851.c b/drivers/net/ks8851.c
> index b4fb07a..6da81e1 100644
> --- a/drivers/net/ks8851.c
> +++ b/drivers/net/ks8851.c
> @@ -504,7 +504,7 @@ static void ks8851_rx_pkts(struct ks8851_net *ks)
>                                ks->rc_rxqcr | RXQCR_SDA | RXQCR_ADRFE);
> 
>                 if (rxlen > 0) {
> -                       skb = netdev_alloc_skb(ks->netdev, rxlen + 2 + 8);
> +                       skb = netdev_alloc_skb(ks->netdev, rxlen + 4 + 8);
>                         if (!skb) {
> 
> Best Regards
> Abraham
> 

Yes that makes sense, nr_frag is right after the packet (padded to L1
cache size)

But please do the correct allocation ?

Also, we dont need FCS ?

diff --git a/drivers/net/ks8851.c b/drivers/net/ks8851.c
index b4fb07a..05bd312 100644
--- a/drivers/net/ks8851.c
+++ b/drivers/net/ks8851.c
@@ -503,8 +503,9 @@ static void ks8851_rx_pkts(struct ks8851_net *ks)
 		ks8851_wrreg16(ks, KS_RXQCR,
 			       ks->rc_rxqcr | RXQCR_SDA | RXQCR_ADRFE);
 
-		if (rxlen > 0) {
-			skb = netdev_alloc_skb(ks->netdev, rxlen + 2 + 8);
+		if (rxlen > 4) {
+			rxlen -= 4;
+			skb = netdev_alloc_skb(ks->netdev, 2 + 8 + ALIGN(rxlen, 4));
 			if (!skb) {
 				/* todo - dump frame and move on */
 			}
@@ -513,7 +514,7 @@ static void ks8851_rx_pkts(struct ks8851_net *ks)
 			 * for the status header and 4 bytes of garbage */
 			skb_reserve(skb, 2 + 4 + 4);
 
-			rxpkt = skb_put(skb, rxlen - 4) - 8;
+			rxpkt = skb_put(skb, rxlen) - 8;
 
 			/* align the packet length to 4 bytes, and add 4 bytes
 			 * as we're getting the rx status header as well */
@@ -526,7 +527,7 @@ static void ks8851_rx_pkts(struct ks8851_net *ks)
 			netif_rx(skb);
 
 			ks->netdev->stats.rx_packets++;
-			ks->netdev->stats.rx_bytes += rxlen - 4;
+			ks->netdev->stats.rx_bytes += rxlen;
 		}
 
 		ks8851_wrreg16(ks, KS_RXQCR, ks->rc_rxqcr);


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