brcmfmac: only call brcmf_cfg80211_detach() when attach was successful

In brcmf_bus_start() the function brcmf_cfg80211_attach() is called which
may fail. If this happens we should not call brcmf_cfg80211_detach() in
the failure path as it will result in NULL pointer dereference:

  brcmf_fweh_activate_events: Set event_msgs error (-5)
  brcmf_bus_start: failed: -5
  brcmf_sdio_firmware_callback: dongle is not responding
  BUG: unable to handle kernel NULL pointer dereference at 0000000000000068
  IP: [<ffffffff811e8f08>] kernfs_find_ns+0x18/0xd0
  PGD 0
  Oops: 0000 [#1] SMP
  Modules linked in: brcmfmac(O) brcmutil(O) cfg80211 auth_rpcgss
  CPU: 1 PID: 45 Comm: kworker/1:1 Tainted: G           O
  Hardware name: Dell Inc. Latitude E6410/07XJP9, BIOS A07 02/15/2011
  Workqueue: events request_firmware_work_func
  task: ffff880036c09ac0 ti: ffff880036dd4000 task.ti: ffff880036dd4000
  RIP: 0010:[<ffffffff811e8f08>]  [<ffffffff811e8f08>] kernfs_find_ns+0x18/0xd0
  RSP: 0018:ffff880036dd7a28  EFLAGS: 00010246
  RAX: ffff880036c09ac0 RBX: 0000000000000000 RCX: 000000007fffffff
  RDX: 0000000000000000 RSI: ffffffff816578b9 RDI: 0000000000000000
  RBP: ffff880036dd7a48 R08: 0000000000000000 R09: ffff880036c0b340
  R10: 00000000000002ec R11: ffff880036dd7b08 R12: ffffffff816578b9
  R13: 0000000000000000 R14: ffffffff816578b9 R15: ffff8800c6c87000
  FS:  0000000000000000(0000) GS:ffff88012bc40000(0000) knlGS:0000000000000000
  CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
  CR2: 0000000000000068 CR3: 0000000001a0b000 CR4: 00000000000006e0
  Stack:
   0000000000000000 ffffffff816578b9 0000000000000000 ffff8800c0d003c8
   ffff880036dd7a78 ffffffff811e8ff5 0000000ffffffff1 ffffffff81a9b060
   ffff8800c789f880 ffff8800c0d00000 ffff880036dd7a98 ffffffff811ebe0d
  Call Trace:
   [<ffffffff811e8ff5>] kernfs_find_and_get_ns+0x35/0x60
   [<ffffffff811ebe0d>] sysfs_unmerge_group+0x1d/0x60
   [<ffffffff81404ef2>] dpm_sysfs_remove+0x22/0x60
   [<ffffffff813f9db9>] device_del+0x49/0x240
   [<ffffffff815da768>] rfkill_unregister+0x58/0xc0
   [<ffffffffa06bd91b>] wiphy_unregister+0xab/0x2f0 [cfg80211]
   [<ffffffffa0742fe3>] brcmf_cfg80211_detach+0x23/0x50 [brcmfmac]
   [<ffffffffa074d986>] brcmf_detach+0x86/0xe0 [brcmfmac]
   [<ffffffffa0757de8>] brcmf_sdio_remove+0x48/0x120 [brcmfmac]
   [<ffffffffa0758ed9>] brcmf_sdiod_remove+0x29/0xd0 [brcmfmac]
   [<ffffffffa0759031>] brcmf_ops_sdio_remove+0xb1/0x110 [brcmfmac]
   [<ffffffffa001c267>] sdio_bus_remove+0x37/0x100 [mmc_core]
   [<ffffffff813fe026>] __device_release_driver+0x96/0x130
   [<ffffffff813fe0e3>] device_release_driver+0x23/0x30
   [<ffffffffa0754bc8>] brcmf_sdio_firmware_callback+0x2a8/0x5d0 [brcmfmac]
   [<ffffffffa074deaf>] brcmf_fw_request_nvram_done+0x15f/0x5e0 [brcmfmac]
   [<ffffffff8140142f>] ? devres_add+0x3f/0x50
   [<ffffffff810642b5>] ? usermodehelper_read_unlock+0x15/0x20
   [<ffffffff81400000>] ? platform_match+0x70/0xa0
   [<ffffffff8140f400>] request_firmware_work_func+0x30/0x60
   [<ffffffff8106828c>] process_one_work+0x14c/0x3d0
   [<ffffffff8106862a>] worker_thread+0x11a/0x450
   [<ffffffff81068510>] ? process_one_work+0x3d0/0x3d0
   [<ffffffff8106d692>] kthread+0xd2/0xf0
   [<ffffffff8106d5c0>] ? kthread_create_on_node+0x180/0x180
   [<ffffffff815ed35f>] ret_from_fork+0x3f/0x70
   [<ffffffff8106d5c0>] ? kthread_create_on_node+0x180/0x180
  Code: e9 40 fe ff ff 48 89 d8 eb 87 66 0f 1f 84 00 00 00 00 00 66 66 66 66
	90 55 48 89 e5 41 56 49 89 f6 41 55 49 89 d5 31 d2 41 54 53 <0f> b7
	47 68 48 8b 5f 48 66 c1 e8 05 83 e0 01 4d 85 ed 0f b6 c8
  RIP  [<ffffffff811e8f08>] kernfs_find_ns+0x18/0xd0
   RSP <ffff880036dd7a28>
  CR2: 0000000000000068
  ---[ end trace 87d6ec0d3fe46740 ]---
Reported-by: Daniel (Deognyoun) Kim <dekim@broadcom.com>
Reviewed-by: Hante Meuleman <meuleman@broadcom.com>
Reviewed-by: Franky (Zhenhui) Lin <frankyl@broadcom.com>
Reviewed-by: Pieter-Paul Giesberts <pieterpg@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>

drivers/net/wireless/brcm80211/brcmfmac/core.c

@@ -1049,7 +1049,10 @@ int brcmf_bus_start(struct device *dev)
 fail:
 	if (ret < 0) {
 		brcmf_err("failed: %d\n", ret);
+		if (drvr->config) {
 			brcmf_cfg80211_detach(drvr->config);
+			drvr->config = NULL;
+		}
 		if (drvr->fws) {
 			brcmf_fws_del_interface(ifp);
 			brcmf_fws_deinit(drvr);