brcmfmac: fix Oops when bringing up interface during USB disconnect

Fix a race which leads to an Oops with NULL pointer dereference.  The
dereference is in brcmf_config_dongle() when cfg_to_ndev() attempts to get
net_device structure of interface with index 0 via if2bss mapping. This
shouldn't fail because of check for bus being ready in brcmf_netdev_open(),
but it's not synchronised with USB disconnect and there is a race: after
the check the bus can be marked down and the mapping for interface 0 may be
gone.

Solve this by modifying disconnect handling so that the removal of mapping
of ifidx to brcmf_if structure happens after netdev removal (which is
synchronous with brcmf_netdev_open() thanks to rtln being locked in
devinet_ioctl()). This assures brcmf_netdev_open() returns before the
mapping is removed during disconnect.

Unable to handle kernel NULL pointer dereference at virtual address 00000008
pgd = bcae2612
[00000008] *pgd=8be73831
Internal error: Oops: 17 [#1] PREEMPT SMP ARM
Modules linked in: brcmfmac brcmutil nf_log_ipv4 nf_log_common xt_LOG xt_limit
iptable_mangle xt_connmark xt_tcpudp xt_conntrack nf_conntrack nf_defrag_ipv6
nf_defrag_ipv4 iptable_filter ip_tables x_tables usb_f_mass_storage usb_f_rndis
u_ether usb_serial_simple usbserial cdc_acm smsc95xx usbnet ci_hdrc_imx ci_hdrc
usbmisc_imx ulpi 8250_exar 8250_pci 8250 8250_base libcomposite configfs
udc_core [last unloaded: brcmutil]
CPU: 2 PID: 24478 Comm: ifconfig Not tainted 4.19.23-00078-ga62866d-dirty #115
Hardware name: Freescale i.MX6 Quad/DualLite (Device Tree)
PC is at brcmf_cfg80211_up+0x94/0x29c [brcmfmac]
LR is at brcmf_cfg80211_up+0x8c/0x29c [brcmfmac]
pc : [<7f26a91c>]    lr : [<7f26a914>]    psr: a0070013
sp : eca99d28  ip : 00000000  fp : ee9c6c00
r10: 00000036  r9 : 00000000  r8 : ece4002c
r7 : edb5b800  r6 : 00000000  r5 : 80f08448  r4 : edb5b968
r3 : ffffffff  r2 : 00000000  r1 : 00000002  r0 : 00000000
Flags: NzCv  IRQs on  FIQs on  Mode SVC_32  ISA ARM  Segment none
Control: 10c5387d  Table: 7ca0c04a  DAC: 00000051
Process ifconfig (pid: 24478, stack limit = 0xd9e85a0e)
Stack: (0xeca99d28 to 0xeca9a000)
9d20:                   00000000 80f873b0 0000000d 80f08448 eca99d68 50d45f32
9d40: 7f27de94 ece40000 80f08448 80f08448 7f27de94 ece4002c 00000000 00000036
9d60: ee9c6c00 7f27262c 00001002 50d45f32 ece40000 00000000 80f08448 80772008
9d80: 00000001 00001043 00001002 ece40000 00000000 50d45f32 ece40000 00000001
9da0: 80f08448 00001043 00001002 807723d0 00000000 50d45f32 80f08448 eca99e58
9dc0: 80f87113 50d45f32 80f08448 ece40000 ece40138 00001002 80f08448 00000000
9de0: 00000000 80772434 edbd5380 eca99e58 edbd5380 80f08448 ee9c6c0c 80805f70
9e00: 00000000 ede08e00 00008914 ece40000 00000014 ee9c6c0c 600c0013 00001043
9e20: 0208a8c0 ffffffff 00000000 50d45f32 eca98000 80f08448 7ee9fc38 00008914
9e40: 80f68e40 00000051 eca98000 00000036 00000003 80808b9c 6e616c77 00000030
9e60: 00000000 00000000 00001043 0208a8c0 ffffffff 00000000 80f08448 00000000
9e80: 00000000 816d8b20 600c0013 00000001 ede09320 801763d4 00000000 50d45f32
9ea0: eca98000 80f08448 7ee9fc38 50d45f32 00008914 80f08448 7ee9fc38 80f68e40
9ec0: ed531540 8074721c 00000800 00000001 00000000 6e616c77 00000030 00000000
9ee0: 00000000 00001002 0208a8c0 ffffffff 00000000 50d45f32 80f08448 7ee9fc38
9f00: ed531560 ec8fc900 80285a6c 80285138 edb910c0 00000000 ecd91008 ede08e00
9f20: 80f08448 00000000 00000000 816d8b20 600c0013 00000001 ede09320 801763d4
9f40: 00000000 50d45f32 00021000 edb91118 edb910c0 80f08448 01b29000 edb91118
9f60: eca99f7c 50d45f32 00021000 ec8fc900 00000003 ec8fc900 00008914 7ee9fc38
9f80: eca98000 00000036 00000003 80285a6c 00086364 7ee9fe1c 000000c3 00000036
9fa0: 801011c4 80101000 00086364 7ee9fe1c 00000003 00008914 7ee9fc38 00086364
9fc0: 00086364 7ee9fe1c 000000c3 00000036 0008630c 7ee9fe1c 7ee9fc38 00000003
9fe0: 000a42b8 7ee9fbd4 00019914 76e09acc 600c0010 00000003 00000000 00000000
[<7f26a91c>] (brcmf_cfg80211_up [brcmfmac]) from [<7f27262c>] (brcmf_netdev_open+0x74/0xe8 [brcmfmac])
[<7f27262c>] (brcmf_netdev_open [brcmfmac]) from [<80772008>] (__dev_open+0xcc/0x150)
[<80772008>] (__dev_open) from [<807723d0>] (__dev_change_flags+0x168/0x1b4)
[<807723d0>] (__dev_change_flags) from [<80772434>] (dev_change_flags+0x18/0x48)
[<80772434>] (dev_change_flags) from [<80805f70>] (devinet_ioctl+0x67c/0x79c)
[<80805f70>] (devinet_ioctl) from [<80808b9c>] (inet_ioctl+0x210/0x3d4)
[<80808b9c>] (inet_ioctl) from [<8074721c>] (sock_ioctl+0x350/0x524)
[<8074721c>] (sock_ioctl) from [<80285138>] (do_vfs_ioctl+0xb0/0x9b0)
[<80285138>] (do_vfs_ioctl) from [<80285a6c>] (ksys_ioctl+0x34/0x5c)
[<80285a6c>] (ksys_ioctl) from [<80101000>] (ret_fast_syscall+0x0/0x28)
Exception stack(0xeca99fa8 to 0xeca99ff0)
9fa0:                   00086364 7ee9fe1c 00000003 00008914 7ee9fc38 00086364
9fc0: 00086364 7ee9fe1c 000000c3 00000036 0008630c 7ee9fe1c 7ee9fc38 00000003
9fe0: 000a42b8 7ee9fbd4 00019914 76e09acc
Code: e5970328 eb002021 e1a02006 e3a01002 (e5909008)
---[ end trace 5cbac2333f3ac5df ]---
Signed-off-by: Piotr Figiel <p.figiel@camlintechnologies.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>

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

@@ -841,17 +841,17 @@ static void brcmf_del_if(struct brcmf_pub *drvr, s32 bsscfgidx,
 			 bool rtnl_locked)
 {
 	struct brcmf_if *ifp;
+	int ifidx;
 
 	ifp = drvr->iflist[bsscfgidx];
-	drvr->iflist[bsscfgidx] = NULL;
 	if (!ifp) {
 		bphy_err(drvr, "Null interface, bsscfgidx=%d\n", bsscfgidx);
 		return;
 	}
 	brcmf_dbg(TRACE, "Enter, bsscfgidx=%d, ifidx=%d\n", bsscfgidx,
 		  ifp->ifidx);
-	if (drvr->if2bss[ifp->ifidx] == bsscfgidx)
-		drvr->if2bss[ifp->ifidx] = BRCMF_BSSIDX_INVALID;
+	ifidx = ifp->ifidx;
+
 	if (ifp->ndev) {
 		if (bsscfgidx == 0) {
 			if (ifp->ndev->netdev_ops == &brcmf_netdev_ops_pri) {
@@ -879,6 +879,10 @@ static void brcmf_del_if(struct brcmf_pub *drvr, s32 bsscfgidx,
 		brcmf_p2p_ifp_removed(ifp, rtnl_locked);
 		kfree(ifp);
 	}
+
+	drvr->iflist[bsscfgidx] = NULL;
+	if (drvr->if2bss[ifidx] == bsscfgidx)
+		drvr->if2bss[ifidx] = BRCMF_BSSIDX_INVALID;
 }
 
 void brcmf_remove_interface(struct brcmf_if *ifp, bool rtnl_locked)