Possible bug in net/ipv4/route.c?
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From: Sol Kavy on 1 Jul 2010 20:30 Found Linux: 2.6.28 Arch: Ubicom32 <not yet pushed> Project: uCLinux based Router Test: Bit torrent Stress Test Note: The top of Linus git net/ipv4/route.c appears to have the same issue. The following is a patch for clearing out IP options area in an input skb during link failure processing.� Without this patch, the icmp_send() can result in a call to ip_options_echo() where the common buffer area of the skb is incorrectly interpreted.� Depending on the previous use of the skb->cb[], the interpreted option length values can cause stack corruption by copying more than 40 bytes to the output options. In our case, a driver is using the skb->cb[] area to hold driver specific data. The driver is not zeroing out the area after use. I can see three basic solutions: 1) Drivers are not allowed to use the skb->cb[] area at all. Ubicom should modify the driver to use a different approach. 2) The layer using skb->cb[] should clear this area after use and before handing the skb to another layer. Ubicom should modify the driver to clear the skb->cb[] area before sending it up the line. 3) Any layer that "uses" the skb->cb[] area must clear the area before use. In which case, the proposed patch would fix the problem for the ipv4_link_failure(). I believe that this is the correct fix because I see ip_rcv() clears the skb->cb[] before using it. Can someone confirm that this is the appropriate fix?� If this is documented somewhere, please direct me to the documentation. Please send email to sol(a)ubicom.com in addition to posting your response. Thanks, Sol Kavy/Murat Sezgin Ubicom, Inc. Patch:� diff --git a/net/ipv4/route.c b/net/ipv4/route.c index 125ee64..d13805f 100644 --- a/net/ipv4/route.c +++ b/net/ipv4/route.c @@ -1606,6 +1606,14 @@ static void ipv4_link_failure(struct sk_buff *skb) { ������� struct rtable *rt; +���� ��/* +�������� * Since link failure can be called with skbs from many layers (see arp) +�������� * the cb area of the skb must be cleared before use. Because the cb area +�������� * can be formatted according to the caller layer's cb area format and it may cause +�������� * corruptions when it is handled in a different network layer. +�������� */ +������ memset(&(IPCB(skb)->opt), 0, sizeof(IPCB(skb)->opt)); ������� icmp_send(skb, ICMP_DEST_UNREACH, ICMP_HOST_UNREACH, 0); ��������rt = skb->rtable; The packet is enqueud by: do_IRQ()->do_softirq()->__do_softirq()->net_rx_action()->ubi32_eth_napi_poll()->ubi32_eth_receive()->__vlan_hwaccel_rx()->netif_receive_skb()->br_handle_frame()->nf_hook_slow()->br_nf_pre_routing_finish()->br_nfr_pre_routing_finish_bridge()->neight_resolve_output()->__neigh_event_send(). The packet is then dequeued by: do_IRQ() -> irq_exit() -> do_softirq() -> run_timer_softirq() -> neigh_timer_handler() -> arp_error_report() -> ipv4_link_failure() -> icmp_send() -> ip_options_echo(). Because the Ubicom Ethernet driver overwrites the common buffer area, the enqueued packet contains garbage when casted as an IP options data structure. This results in ip_options_echo() miss reading the option length information and overwriting memory.� By clearing the skb->cb[] before processing the icmp_send() against the packet, we ensure that ip_options_echo() does not corrupt memory.�� -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ |