wifi: brcmfmac: Check the count value of channel spec to prevent out-of-bounds reads

In the Linux kernel, the following vulnerability has been resolved:

wifi: brcmfmac: Check the count value of channel spec to prevent out-of-bounds reads

This patch fixes slab-out-of-bounds reads in brcmfmac that occur in
brcmf_construct_chaninfo() and brcmf_enable_bw40_2g() when the count
value of channel specifications provided by the device is greater than
the length of 'list->element[]', decided by the size of the 'list'
allocated with kzalloc(). The patch adds checks that make the functions
free the buffer and return -EINVAL if that is the case. Note that the
negative return is handled by the caller, brcmf_setup_wiphybands() or
brcmf_cfg80211_attach().

Found by a modified version of syzkaller.

Crash Report from brcmf_construct_chaninfo():
==================================================================
BUG: KASAN: slab-out-of-bounds in brcmf_setup_wiphybands+0x1238/0x1430
Read of size 4 at addr ffff888115f24600 by task kworker/0:2/1896

CPU: 0 PID: 1896 Comm: kworker/0:2 Tainted: G W O 5.14.0+ #132
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.12.1-0-ga5cab58e9a3f-prebuilt.qemu.org 04/01/2014
Workqueue: usb_hub_wq hub_event
Call Trace:
dump_stack_lvl+0x57/0x7d
print_address_description.constprop.0.cold+0x93/0x334
kasan_report.cold+0x83/0xdf
brcmf_setup_wiphybands+0x1238/0x1430
brcmf_cfg80211_attach+0x2118/0x3fd0
brcmf_attach+0x389/0xd40
brcmf_usb_probe+0x12de/0x1690
usb_probe_interface+0x25f/0x710
really_probe+0x1be/0xa90
__driver_probe_device+0x2ab/0x460
driver_probe_device+0x49/0x120
__device_attach_driver+0x18a/0x250
bus_for_each_drv+0x123/0x1a0
__device_attach+0x207/0x330
bus_probe_device+0x1a2/0x260
device_add+0xa61/0x1ce0
usb_set_configuration+0x984/0x1770
usb_generic_driver_probe+0x69/0x90
usb_probe_device+0x9c/0x220
really_probe+0x1be/0xa90
__driver_probe_device+0x2ab/0x460
driver_probe_device+0x49/0x120
__device_attach_driver+0x18a/0x250
bus_for_each_drv+0x123/0x1a0
__device_attach+0x207/0x330
bus_probe_device+0x1a2/0x260
device_add+0xa61/0x1ce0
usb_new_device.cold+0x463/0xf66
hub_event+0x10d5/0x3330
process_one_work+0x873/0x13e0
worker_thread+0x8b/0xd10
kthread+0x379/0x450
ret_from_fork+0x1f/0x30

Allocated by task 1896:
kasan_save_stack+0x1b/0x40
__kasan_kmalloc+0x7c/0x90
kmem_cache_alloc_trace+0x19e/0x330
brcmf_setup_wiphybands+0x290/0x1430
brcmf_cfg80211_attach+0x2118/0x3fd0
brcmf_attach+0x389/0xd40
brcmf_usb_probe+0x12de/0x1690
usb_probe_interface+0x25f/0x710
really_probe+0x1be/0xa90
__driver_probe_device+0x2ab/0x460
driver_probe_device+0x49/0x120
__device_attach_driver+0x18a/0x250
bus_for_each_drv+0x123/0x1a0
__device_attach+0x207/0x330
bus_probe_device+0x1a2/0x260
device_add+0xa61/0x1ce0
usb_set_configuration+0x984/0x1770
usb_generic_driver_probe+0x69/0x90
usb_probe_device+0x9c/0x220
really_probe+0x1be/0xa90
__driver_probe_device+0x2ab/0x460
driver_probe_device+0x49/0x120
__device_attach_driver+0x18a/0x250
bus_for_each_drv+0x123/0x1a0
__device_attach+0x207/0x330
bus_probe_device+0x1a2/0x260
device_add+0xa61/0x1ce0
usb_new_device.cold+0x463/0xf66
hub_event+0x10d5/0x3330
process_one_work+0x873/0x13e0
worker_thread+0x8b/0xd10
kthread+0x379/0x450
ret_from_fork+0x1f/0x30

The buggy address belongs to the object at ffff888115f24000
which belongs to the cache kmalloc-2k of size 2048
The buggy address is located 1536 bytes inside of
2048-byte region [ffff888115f24000, ffff888115f24800)

Memory state around the buggy address:
ffff888115f24500: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
ffff888115f24580: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffff888115f24600: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
^
ffff888115f24680: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff888115f24700: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================

Crash Report from brcmf_enable_bw40_2g():
==========
---truncated---