Re: [lockup] 2.6.17-rc3: netfilter/sctp: lockup in sctp_new(), do_basic_checks()

Ingo Molnar
2006-05-02T13:36:13Z

* Ingo Molnar <mingo@elte.hu> wrote:

> running an "isic" stresstest on and against a testbox [which, amongst
> other things, generates random incoming and outgoing packets] on
> 2.6.17-rc3 (and 2.6.17-rc3-mm1) over gigabit results in a reproducible
> lockup, after 5-10 minutes of runtime:
>
> BUG: soft lockup detected on CPU#0!
> [<c0104e7f>] show_trace+0xd/0xf
> [<c0104e96>] dump_stack+0x15/0x17
> [<c015ad02>] softlockup_tick+0xc5/0xd9
> [<c0134c02>] run_local_timers+0x22/0x24
> [<c0134fb7>] update_process_times+0x40/0x65
> [<c011aa56>] smp_apic_timer_interrupt+0x58/0x60
> [<c010492b>] apic_timer_interrupt+0x27/0x2c
> [<c0f00df9>] sctp_new+0x8b/0x235
> [<c0ef9666>] ip_conntrack_in+0x175/0x4ca
> [<c0eb6dd7>] nf_iterate+0x31/0x94
> [<c0eb6e83>] nf_hook_slow+0x49/0xda
> [<c0ec2f55>] ip_rcv+0x24c/0x567
> [<c0e7dec4>] netif_receive_skb+0x34b/0x397
> [<c07870cb>] rtl8139_poll+0x3d8/0x5db
> [<c0e7c7ad>] net_rx_action+0x9b/0x1ba
> [<c0131955>] __do_softirq+0x6e/0xec
> [<c0106187>] do_softirq+0x59/0xcd

thinking about it, what prevents the SCTP chunk's len field from being
zero, and thus causing an infinite loop in for_each_sctp_chunk()? The
patch below should fix that.

Ingo

----
From: Ingo Molnar <mingo@elte.hu>

fix infinite loop in the SCTP-netfilter code: check SCTP chunk size to
guarantee progress of for_each_sctp_chunk(). (all other uses of
for_each_sctp_chunk() are preceded by do_basic_checks(), so this fix
should be complete.)

Signed-off-by: Ingo Molnar <mingo@elte.hu>

Index: linux/net/ipv4/netfilter/ip_conntrack_proto_sctp.c
===================================================================
--- linux.orig/net/ipv4/netfilter/ip_conntrack_proto_sctp.c
+++ linux/net/ipv4/netfilter/ip_conntrack_proto_sctp.c
@@ -227,6 +227,15 @@ static int do_basic_checks(struct ip_con
flag = 0;

for_each_sctp_chunk (skb, sch, _sch, offset, count) {
+ unsigned int len = (htons(sch->length) + 3) & ~3;
+
+ /*
+ * Dont get into a loop with zero-sized or negative
+ * length values:
+ */
+ if (!len || len >= skb->len)
+ goto fail;
+
DEBUGP("Chunk Num: %d Type: %d\n", count, sch->type);

if (sch->type == SCTP_CID_INIT
@@ -241,6 +250,7 @@ static int do_basic_checks(struct ip_con
|| sch->type == SCTP_CID_COOKIE_ECHO
|| flag)
&& count !=0 ) {
+fail:
DEBUGP("Basic checks failed\n");
return 1;
}