If ICMP6 message with "Packet Too Big" is received after send SCTP DATA,
kernel panic will occur when SCTP DATA is send again.

This is because of a bad dest address when call to skb_copy_bits().

The messages sequence is like this:

Endpoint A                             Endpoint B
                               <-------  SCTP DATA (size=1432)
ICMP6 message ------->
(Packet Too Big pmtu=1280)
                               <-------  Resend SCTP DATA (size=1432)
------------kernel panic---------------

 printing eip:
c05be62a
*pde = 00000000
Oops: 0002 [#1]
SMP
Modules linked in: scomm l2cap bluetooth ipv6 dm_mirror dm_mod video output sbs battery lp floppy sg i2c_piix4 i2c_core pcnet32 mii button ac parport_pc parport ide_cd cdrom serio_raw mptspi mptscsih mptbase scsi_transport_spi sd_mod scsi_mod ext3 jbd ehci_hcd ohci_hcd uhci_hcd
CPU:    0
EIP:    0060:[<c05be62a>]    Not tainted VLI
EFLAGS: 00010282   (2.6.23-rc2 #1)
EIP is at skb_copy_bits+0x4f/0x1ef
eax: 000004d0   ebx: ce12a980   ecx: 00000134   edx: cfd5a880
esi: c8246858   edi: 00000000   ebp: c0759b14   esp: c0759adc
ds: 007b   es: 007b   fs: 00d8  gs: 0000  ss: 0068
Process swapper (pid: 0, ti=c0759000 task=c06d0340 task.ti=c0713000)
Stack: c0759b88 c0405867 ce12a980 c8bff838 c789c084 00000000 00000028 cfd5a880
       d09f1890 000005dc 0000007b ce12a980 cfd5a880 c8bff838 c0759b88 d09bc521
       000004d0 fffff96c 00000200 00000100 c0759b50 cfd5a880 00000246 c0759bd4
Call Trace:
 [<c0405e1d>] show_trace_log_lvl+0x1a/0x2f
 [<c0405ecd>] show_stack_log_lvl+0x9b/0xa3
 [<c040608d>] show_registers+0x1b8/0x289
 [<c0406271>] die+0x113/0x246
 [<c0625dbc>] do_page_fault+0x4ad/0x57e
 [<c0624642>] error_code+0x72/0x78
 [<d09bc521>] ip6_output+0x8e5/0xab2 [ipv6]
 [<d09bcec1>] ip6_xmit+0x2ea/0x3a3 [ipv6]
 [<d0a3f2ca>] sctp_v6_xmit+0x248/0x253 [sctp]
 [<d0a3c934>] sctp_packet_transmit+0x53f/0x5ae [sctp]
 [<d0a34bf8>] sctp_outq_flush+0x555/0x587 [sctp]
 [<d0a34d3c>] sctp_retransmit+0xf8/0x10f [sctp]
 [<d0a3d183>] sctp_icmp_frag_needed+0x57/0x5b [sctp]
 [<d0a3ece2>] sctp_v6_err+0xcd/0x148 [sctp]
 [<d09cf1ce>] icmpv6_notify+0xe6/0x167 [ipv6]
 [<d09d009a>] icmpv6_rcv+0x7d7/0x849 [ipv6]
 [<d09be240>] ip6_input+0x1dc/0x310 [ipv6]
 [<d09be965>] ipv6_rcv+0x294/0x2df [ipv6]
 [<c05c3789>] netif_receive_skb+0x2d2/0x335
 [<c05c5733>] process_backlog+0x7f/0xd0
 [<c05c58f6>] net_rx_action+0x96/0x17e
 [<c042e722>] __do_softirq+0x64/0xcd
 [<c0406f37>] do_softirq+0x5c/0xac
 =======================
Code: 00 00 29 ca 89 d0 2b 45 e0 89 55 ec 85 c0 7e 35 39 45 08 8b 55 e4 0f 4e 45 08 8b 75 e0 8b 7d dc 89 c1 c1 e9 02 03 b2 a0 00 00 00 <f3> a5 89 c1 83 e1 03 74 02 f3 a4 29 45 08 0f 84 7b 01 00 00 01
EIP: [<c05be62a>] skb_copy_bits+0x4f/0x1ef SS:ESP 0068:c0759adc
Kernel panic - not syncing: Fatal exception in interrupt

Arnaldo says:
====================
Thanks! I'm to blame for this one, problem was introduced in:

b0e380b1

@@ -761,7 +762,7 @@ slow_path:
                /*
                 *      Copy a block of the IP datagram.
                 */
-               if (skb_copy_bits(skb, ptr, frag->h.raw, len))
+               if (skb_copy_bits(skb, ptr, skb_transport_header(skb),
len))
                        BUG();
                left -= len;
====================
Signed-off-by: Wei Yongjun <yjwei@cn.fujitsu.com>
Acked-by: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
Signed-off-by: Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
Signed-off-by: David S. Miller <davem@davemloft.net>