mwifiex_get_priv_by_id() returns the priv pointer corresponding to
the bss_num and bss_type, but without checking if the priv is actually
currently in use.
Unused priv pointers do not have a wiphy attached to them which can
lead to NULL pointer dereferences further down the callstack.  Fix
this by returning only used priv pointers which have priv->bss_mode
set to something else than NL80211_IFTYPE_UNSPECIFIED.

Said NULL pointer dereference happened when an Accesspoint was started
with wpa_supplicant -i mlan0 with this config:

network={
        ssid="somessid"
        mode=2
        frequency=2412
        key_mgmt=WPA-PSK WPA-PSK-SHA256
        proto=RSN
        group=CCMP
        pairwise=CCMP
        psk="12345678"
}

When waiting for the AP to be established, interrupting wpa_supplicant
with <ctrl-c> and starting it again this happens:

| Unable to handle kernel NULL pointer dereference at virtual address 0000000000000140
| Mem abort info:
|   ESR = 0x0000000096000004
|   EC = 0x25: DABT (current EL), IL = 32 bits
|   SET = 0, FnV = 0
|   EA = 0, S1PTW = 0
|   FSC = 0x04: level 0 translation fault
| Data abort info:
|   ISV = 0, ISS = 0x00000004, ISS2 = 0x00000000
|   CM = 0, WnR = 0, TnD = 0, TagAccess = 0
|   GCS = 0, Overlay = 0, DirtyBit = 0, Xs = 0
| user pgtable: 4k pages, 48-bit VAs, pgdp=0000000046d96000
| [0000000000000140] pgd=0000000000000000, p4d=0000000000000000
| Internal error: Oops: 0000000096000004 [#1] PREEMPT SMP
| Modules linked in: caam_jr caamhash_desc spidev caamalg_desc crypto_engine authenc libdes mwifiex_sdio
+mwifiex crct10dif_ce cdc_acm onboard_usb_hub fsl_imx8_ddr_perf imx8m_ddrc rtc_ds1307 lm75 rtc_snvs
+imx_sdma caam imx8mm_thermal spi_imx error imx_cpufreq_dt fuse ip_tables x_tables ipv6
| CPU: 0 PID: 8 Comm: kworker/0:1 Not tainted 6.9.0-00007-g937242013fce-dirty #18
| Hardware name: somemachine (DT)
| Workqueue: events sdio_irq_work
| pstate: 00000005 (nzcv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
| pc : mwifiex_get_cfp+0xd8/0x15c [mwifiex]
| lr : mwifiex_get_cfp+0x34/0x15c [mwifiex]
| sp : ffff8000818b3a70
| x29: ffff8000818b3a70 x28: ffff000006bfd8a5 x27: 0000000000000004
| x26: 000000000000002c x25: 0000000000001511 x24: 0000000002e86bc9
| x23: ffff000006bfd996 x22: 0000000000000004 x21: ffff000007bec000
| x20: 000000000000002c x19: 0000000000000000 x18: 0000000000000000
| x17: 000000040044ffff x16: 00500072b5503510 x15: ccc283740681e517
| x14: 0201000101006d15 x13: 0000000002e8ff43 x12: 002c01000000ffb1
| x11: 0100000000000000 x10: 02e8ff43002c0100 x9 : 0000ffb100100157
| x8 : ffff000003d20000 x7 : 00000000000002f1 x6 : 00000000ffffe124
| x5 : 0000000000000001 x4 : 0000000000000003 x3 : 0000000000000000
| x2 : 0000000000000000 x1 : 0001000000011001 x0 : 0000000000000000
| Call trace:
|  mwifiex_get_cfp+0xd8/0x15c [mwifiex]
|  mwifiex_parse_single_response_buf+0x1d0/0x504 [mwifiex]
|  mwifiex_handle_event_ext_scan_report+0x19c/0x2f8 [mwifiex]
|  mwifiex_process_sta_event+0x298/0xf0c [mwifiex]
|  mwifiex_process_event+0x110/0x238 [mwifiex]
|  mwifiex_main_process+0x428/0xa44 [mwifiex]
|  mwifiex_sdio_interrupt+0x64/0x12c [mwifiex_sdio]
|  process_sdio_pending_irqs+0x64/0x1b8
|  sdio_irq_work+0x4c/0x7c
|  process_one_work+0x148/0x2a0
|  worker_thread+0x2fc/0x40c
|  kthread+0x110/0x114
|  ret_from_fork+0x10/0x20
| Code: a94153f3 a8c37bfd d50323bf d65f03c0 (f940a000)
| ---[ end trace 0000000000000000 ]---
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Acked-by: Brian Norris <briannorris@chromium.org>
Reviewed-by: Francesco Dolcini <francesco.dolcini@toradex.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://patch.msgid.link/20240703072409.556618-1-s.hauer@pengutronix.de