cfg80211: fix looping soft lockup in find_ie()

The find_ie() function uses a size_t for the len parameter, and
directly uses len as a loop variable.  If any received packets
are malformed, it is possible for the decrease of len to overflow,
and since the result is unsigned, the loop will not terminate.
Change it to a signed int so the loop conditional works for
negative values.

This fixes the following soft lockup:

[38573.102007] BUG: soft lockup - CPU#0 stuck for 61s! [phy0:2230]
[38573.102007] Modules linked in: aes_i586 aes_generic fuse af_packet ipt_REJECT xt_tcpudp nf_conntrack_ipv4 nf_defrag_ipv4 xt_state iptable_filter ip_tables x_tables acpi_cpufreq binfmt_misc dm_mirror dm_region_hash dm_log dm_multipath dm_mod kvm_intel kvm uinput i915 arc4 ecb drm snd_hda_codec_idt ath5k snd_hda_intel hid_apple mac80211 usbhid appletouch snd_hda_codec snd_pcm ath cfg80211 snd_timer i2c_algo_bit ohci1394 video snd processor ieee1394 rfkill ehci_hcd sg sky2 backlight snd_page_alloc uhci_hcd joydev output ac thermal button battery sr_mod applesmc cdrom input_polldev evdev unix [last unloaded: scsi_wait_scan]
[38573.102007] irq event stamp: 2547724535
[38573.102007] hardirqs last  enabled at (2547724534): [<c1002ffc>] restore_all_notrace+0x0/0x18
[38573.102007] hardirqs last disabled at (2547724535): [<c10038f4>] apic_timer_interrupt+0x28/0x34
[38573.102007] softirqs last  enabled at (92950144): [<c103ab48>] __do_softirq+0x108/0x210
[38573.102007] softirqs last disabled at (92950274): [<c1348e74>] _spin_lock_bh+0x14/0x80
[38573.102007]
[38573.102007] Pid: 2230, comm: phy0 Tainted: G        W  (2.6.31-rc7-wl #8) MacBook1,1
[38573.102007] EIP: 0060:[<f8ea2d50>] EFLAGS: 00010292 CPU: 0
[38573.102007] EIP is at cmp_ies+0x30/0x180 [cfg80211]
[38573.102007] EAX: 00000082 EBX: 00000000 ECX: ffffffc1 EDX: d8efd014
[38573.102007] ESI: ffffff7c EDI: 0000004d EBP: eee2dc50 ESP: eee2dc3c
[38573.102007]  DS: 007b ES: 007b FS: 00d8 GS: 0000 SS: 0068
[38573.102007] CR0: 8005003b CR2: d8efd014 CR3: 01694000 CR4: 000026d0
[38573.102007] DR0: 00000000 DR1: 00000000 DR2: 00000000 DR3: 00000000
[38573.102007] DR6: ffff0ff0 DR7: 00000400
[38573.102007] Call Trace:
[38573.102007]  [<f8ea2f8d>] cmp_bss+0xed/0x100 [cfg80211]
[38573.102007]  [<f8ea33e4>] cfg80211_bss_update+0x84/0x410 [cfg80211]
[38573.102007]  [<f8ea3884>] cfg80211_inform_bss_frame+0x114/0x180 [cfg80211]
[38573.102007]  [<f97255ff>] ieee80211_bss_info_update+0x4f/0x180 [mac80211]
[38573.102007]  [<f972b118>] ieee80211_rx_bss_info+0x88/0xf0 [mac80211]
[38573.102007]  [<f9739297>] ? ieee802_11_parse_elems+0x27/0x30 [mac80211]
[38573.102007]  [<f972b224>] ieee80211_rx_mgmt_probe_resp+0xa4/0x1c0 [mac80211]
[38573.102007]  [<f972bc59>] ieee80211_sta_rx_queued_mgmt+0x919/0xc50 [mac80211]
[38573.102007]  [<c1009707>] ? sched_clock+0x27/0xa0
[38573.102007]  [<c1009707>] ? sched_clock+0x27/0xa0
[38573.102007]  [<c105ffd0>] ? mark_held_locks+0x60/0x80
[38573.102007]  [<c1348be5>] ? _spin_unlock_irqrestore+0x55/0x70
[38573.102007]  [<c134baa5>] ? sub_preempt_count+0x85/0xc0
[38573.102007]  [<c1348bce>] ? _spin_unlock_irqrestore+0x3e/0x70
[38573.102007]  [<c12c1c0f>] ? skb_dequeue+0x4f/0x70
[38573.102007]  [<f972c021>] ieee80211_sta_work+0x91/0xb80 [mac80211]
[38573.102007]  [<c1009707>] ? sched_clock+0x27/0xa0
[38573.102007]  [<c134baa5>] ? sub_preempt_count+0x85/0xc0
[38573.102007]  [<c10479af>] worker_thread+0x18f/0x320
[38573.102007]  [<c104794e>] ? worker_thread+0x12e/0x320
[38573.102007]  [<c1348be5>] ? _spin_unlock_irqrestore+0x55/0x70
[38573.102007]  [<f972bf90>] ? ieee80211_sta_work+0x0/0xb80 [mac80211]
[38573.102007]  [<c104cbb0>] ? autoremove_wake_function+0x0/0x50
[38573.102007]  [<c1047820>] ? worker_thread+0x0/0x320
[38573.102007]  [<c104c854>] kthread+0x84/0x90
[38573.102007]  [<c104c7d0>] ? kthread+0x0/0x90
[38573.102007]  [<c1003ab7>] kernel_thread_helper+0x7/0x10

Cc: stable@kernel.org
Signed-off-by: Bob Copeland <me@bobcopeland.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

net/wireless/scan.c

@@ -141,7 +141,7 @@ void cfg80211_bss_expire(struct cfg80211_registered_device *dev)
 		dev->bss_generation++;
 }
 
-static u8 *find_ie(u8 num, u8 *ies, size_t len)
+static u8 *find_ie(u8 num, u8 *ies, int len)
 {
 	while (len > 2 && ies[0] != num) {
 		len -= ies[1] + 2;