use pskb_may_pull to access ipv6 header correctly for paged skbs
It was omitted in the bridge code leading to crash in blind
__skb_pull

since the skb is cloned undonditionally we also simplify the
the exit path

this fixes bug https://bugzilla.kernel.org/show_bug.cgi?id=25202



Dec 15 14:36:40 User-PC hostapd: wlan0: STA 00:15:00:60:5d:34 IEEE 802.11: authenticated
Dec 15 14:36:40 User-PC hostapd: wlan0: STA 00:15:00:60:5d:34 IEEE 802.11: associated (aid 2)
Dec 15 14:36:40 User-PC hostapd: wlan0: STA 00:15:00:60:5d:34 RADIUS: starting accounting session 4D0608A3-00000005
Dec 15 14:36:41 User-PC kernel: [175576.120287] ------------[ cut here ]------------
Dec 15 14:36:41 User-PC kernel: [175576.120452] kernel BUG at include/linux/skbuff.h:1178!
Dec 15 14:36:41 User-PC kernel: [175576.120609] invalid opcode: 0000 [#1] SMP
Dec 15 14:36:41 User-PC kernel: [175576.120749] last sysfs file: /sys/devices/pci0000:00/0000:00:1f.2/host0/target0:0:0/0:0:0:0/block/sda/uevent
Dec 15 14:36:41 User-PC kernel: [175576.121035] Modules linked in: approvals binfmt_misc bridge stp llc parport_pc ppdev arc4 iwlagn snd_hda_codec_realtek iwlcore i915 snd_hda_intel mac80211 joydev snd_hda_codec snd_hwdep snd_pcm snd_seq_midi drm_kms_helper snd_rawmidi drm snd_seq_midi_event snd_seq snd_timer snd_seq_device cfg80211 eeepc_wmi usbhid psmouse intel_agp i2c_algo_bit intel_gtt uvcvideo agpgart videodev sparse_keymap snd shpchp v4l1_compat lp hid video serio_raw soundcore output snd_page_alloc ahci libahci atl1c
Dec 15 14:36:41 User-PC kernel: [175576.122712]
Dec 15 14:36:41 User-PC kernel: [175576.122769] Pid: 0, comm: kworker/0:0 Tainted: G        W   2.6.37-rc5-wl+ #3 1015PE/1016P
Dec 15 14:36:41 User-PC kernel: [175576.123012] EIP: 0060:[<f83edd65>] EFLAGS: 00010283 CPU: 1
Dec 15 14:36:41 User-PC kernel: [175576.123193] EIP is at br_multicast_rcv+0xc95/0xe1c [bridge]
Dec 15 14:36:41 User-PC kernel: [175576.123362] EAX: 0000001c EBX: f5626318 ECX: 00000000 EDX: 00000000
Dec 15 14:36:41 User-PC kernel: [175576.123550] ESI: ec512262 EDI: f5626180 EBP: f60b5ca0 ESP: f60b5bd8
Dec 15 14:36:41 User-PC kernel: [175576.123737]  DS: 007b ES: 007b FS: 00d8 GS: 00e0 SS: 0068
Dec 15 14:36:41 User-PC kernel: [175576.123902] Process kworker/0:0 (pid: 0, ti=f60b4000 task=f60a8000 task.ti=f60b0000)
Dec 15 14:36:41 User-PC kernel: [175576.124137] Stack:
Dec 15 14:36:41 User-PC kernel: [175576.124181]  ec556500 f6d06800 f60b5be8 c01087d8 ec512262 00000030 00000024 f5626180
Dec 15 14:36:41 User-PC kernel: [175576.124181]  f572c200 ef463440 f5626300 3affffff f6d06dd0 e60766a4 000000c4 f6d06860
Dec 15 14:36:41 User-PC kernel: [175576.124181]  ffffffff ec55652c 00000001 f6d06844 f60b5c64 c0138264 c016e451 c013e47d
Dec 15 14:36:41 User-PC kernel: [175576.124181] Call Trace:
Dec 15 14:36:41 User-PC kernel: [175576.124181]  [<c01087d8>] ? sched_clock+0x8/0x10
Dec 15 14:36:41 User-PC kernel: [175576.124181]  [<c0138264>] ? enqueue_entity+0x174/0x440
Dec 15 14:36:41 User-PC kernel: [175576.124181]  [<c016e451>] ? sched_clock_cpu+0x131/0x190
Dec 15 14:36:41 User-PC kernel: [175576.124181]  [<c013e47d>] ? select_task_rq_fair+0x2ad/0x730
Dec 15 14:36:41 User-PC kernel: [175576.124181]  [<c0524fc1>] ? nf_iterate+0x71/0x90
Dec 15 14:36:41 User-PC kernel: [175576.124181]  [<f83e4914>] ? br_handle_frame_finish+0x184/0x220 [bridge]
Dec 15 14:36:41 User-PC kernel: [175576.124181]  [<f83e4790>] ? br_handle_frame_finish+0x0/0x220 [bridge]
Dec 15 14:36:41 User-PC kernel: [175576.124181]  [<f83e46e9>] ? br_handle_frame+0x189/0x230 [bridge]
Dec 15 14:36:41 User-PC kernel: [175576.124181]  [<f83e4790>] ? br_handle_frame_finish+0x0/0x220 [bridge]
Dec 15 14:36:41 User-PC kernel: [175576.124181]  [<f83e4560>] ? br_handle_frame+0x0/0x230 [bridge]
Dec 15 14:36:41 User-PC kernel: [175576.124181]  [<c04ff026>] ? __netif_receive_skb+0x1b6/0x5b0
Dec 15 14:36:41 User-PC kernel: [175576.124181]  [<c04f7a30>] ? skb_copy_bits+0x110/0x210
Dec 15 14:36:41 User-PC kernel: [175576.124181]  [<c0503a7f>] ? netif_receive_skb+0x6f/0x80
Dec 15 14:36:41 User-PC kernel: [175576.124181]  [<f82cb74c>] ? ieee80211_deliver_skb+0x8c/0x1a0 [mac80211]
Dec 15 14:36:41 User-PC kernel: [175576.124181]  [<f82cc836>] ? ieee80211_rx_handlers+0xeb6/0x1aa0 [mac80211]
Dec 15 14:36:41 User-PC kernel: [175576.124181]  [<c04ff1f0>] ? __netif_receive_skb+0x380/0x5b0
Dec 15 14:36:41 User-PC kernel: [175576.124181]  [<c016e242>] ? sched_clock_local+0xb2/0x190
Dec 15 14:36:41 User-PC kernel: [175576.124181]  [<c012b688>] ? default_spin_lock_flags+0x8/0x10
Dec 15 14:36:41 User-PC kernel: [175576.124181]  [<c05d83df>] ? _raw_spin_lock_irqsave+0x2f/0x50
Dec 15 14:36:41 User-PC kernel: [175576.124181]  [<f82cd621>] ? ieee80211_prepare_and_rx_handle+0x201/0xa90 [mac80211]
Dec 15 14:36:41 User-PC kernel: [175576.124181]  [<f82ce154>] ? ieee80211_rx+0x2a4/0x830 [mac80211]
Dec 15 14:36:41 User-PC kernel: [175576.124181]  [<f815a8d6>] ? iwl_update_stats+0xa6/0x2a0 [iwlcore]
Dec 15 14:36:41 User-PC kernel: [175576.124181]  [<f8499212>] ? iwlagn_rx_reply_rx+0x292/0x3b0 [iwlagn]
Dec 15 14:36:41 User-PC kernel: [175576.124181]  [<c05d83df>] ? _raw_spin_lock_irqsave+0x2f/0x50
Dec 15 14:36:41 User-PC kernel: [175576.124181]  [<f8483697>] ? iwl_rx_handle+0xe7/0x350 [iwlagn]
Dec 15 14:36:41 User-PC kernel: [175576.124181]  [<f8486ab7>] ? iwl_irq_tasklet+0xf7/0x5c0 [iwlagn]
Dec 15 14:36:41 User-PC kernel: [175576.124181]  [<c01aece1>] ? __rcu_process_callbacks+0x201/0x2d0
Dec 15 14:36:41 User-PC kernel: [175576.124181]  [<c0150d05>] ? tasklet_action+0xc5/0x100
Dec 15 14:36:41 User-PC kernel: [175576.124181]  [<c0150a07>] ? __do_softirq+0x97/0x1d0
Dec 15 14:36:41 User-PC kernel: [175576.124181]  [<c05d910c>] ? nmi_stack_correct+0x2f/0x34
Dec 15 14:36:41 User-PC kernel: [175576.124181]  [<c0150970>] ? __do_softirq+0x0/0x1d0
Dec 15 14:36:41 User-PC kernel: [175576.124181]  <IRQ>
Dec 15 14:36:41 User-PC kernel: [175576.124181]  [<c01508f5>] ? irq_exit+0x65/0x70
Dec 15 14:36:41 User-PC kernel: [175576.124181]  [<c05df062>] ? do_IRQ+0x52/0xc0
Dec 15 14:36:41 User-PC kernel: [175576.124181]  [<c01036b0>] ? common_interrupt+0x30/0x38
Dec 15 14:36:41 User-PC kernel: [175576.124181]  [<c03a1fc2>] ? intel_idle+0xc2/0x160
Dec 15 14:36:41 User-PC kernel: [175576.124181]  [<c04daebb>] ? cpuidle_idle_call+0x6b/0x100
Dec 15 14:36:41 User-PC kernel: [175576.124181]  [<c0101dea>] ? cpu_idle+0x8a/0xf0
Dec 15 14:36:41 User-PC kernel: [175576.124181]  [<c05d2702>] ? start_secondary+0x1e8/0x1ee

Cc: David Miller <davem@davemloft.net>
Cc: Johannes Berg <johannes@sipsolutions.net>
Cc: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>