RE: NULL Pointer Deference: NFS & Telnet

Eric Dumazet
2010-09-08T16:15:56Z

Le mardi 07 septembre 2010 à 16:43 -0500, Arce, Abraham a écrit :
> Eric, David,
>
> > From: Eric Dumazet [mailto:eric.dumazet@gmail.com]
>
> [..]
>
> > > 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?
> > >
> >
> > 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 ?
>
> FCS -> CRC is enable in hardware, under ks8851_net_open()
>
> TXCR_TXCRC | /* add CRC */
>
> How about the following patch? I am using added helper function:
> netdev_alloc_skb_ip_align()

Hmm, I prefer following patch (not tested), to really cope with
allocation errors (instead of crashing because of NULL dereference), and
allocate and skb of exactly the needed size.

diff --git a/drivers/net/ks8851.c b/drivers/net/ks8851.c
index b4fb07a..4a4038e 100644
--- a/drivers/net/ks8851.c
+++ b/drivers/net/ks8851.c
@@ -503,30 +503,31 @@ 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 (!skb) {
- /* todo - dump frame and move on */
+ if (rxlen > 4) {
+ unsigned int rxalign;
+
+ rxlen -= 4;
+ rxalign = ALIGN(rxlen, 4);
+ skb = netdev_alloc_skb_ip_align(ks->netdev, rxalign);
+ if (skb) {
+
+ /* 4 bytes of status header + 4 bytes of garbage:
+ * we put them before ethernet header, so that
+ * they are copied, but ignored.
+ */
+ rxpkt = skb_put(skb, rxlen) - 8;
+
+ ks8851_rdfifo(ks, rxpkt, rxalign + 8);
+
+ if (netif_msg_pktdata(ks))
+ ks8851_dbg_dumpkkt(ks, rxpkt);
+
+ skb->protocol = eth_type_trans(skb, ks->netdev);
+ netif_rx(skb);
+
+ ks->netdev->stats.rx_packets++;
+ ks->netdev->stats.rx_bytes += rxlen;
}
-
- /* two bytes to ensure ip is aligned, and four bytes
- * for the status header and 4 bytes of garbage */
- skb_reserve(skb, 2 + 4 + 4);
-
- rxpkt = skb_put(skb, rxlen - 4) - 8;
-
- /* align the packet length to 4 bytes, and add 4 bytes
- * as we're getting the rx status header as well */
- ks8851_rdfifo(ks, rxpkt, ALIGN(rxlen, 4) + 8);
-
- if (netif_msg_pktdata(ks))
- ks8851_dbg_dumpkkt(ks, rxpkt);
-
- skb->protocol = eth_type_trans(skb, ks->netdev);
- netif_rx(skb);
-
- ks->netdev->stats.rx_packets++;
- ks->netdev->stats.rx_bytes += rxlen - 4;
}

ks8851_wrreg16(ks, KS_RXQCR, ks->rc_rxqcr);