ssb: Fix possible NULL pointer dereference in ssb_host_pcmcia_exit

ssb: Fix possible NULL pointer dereference in ssb_host_pcmcia_exit

commit b2c01aab9646ed8ffb7c549afe55d5349c482425 upstream.

Syzkaller report this:

kasan: GPF could be caused by NULL-ptr deref or user memory access
general protection fault: 0000 [#1] SMP KASAN PTI
CPU: 0 PID: 4492 Comm: syz-executor.0 Not tainted 5.0.0-rc7+ #45
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1ubuntu1 04/01/2014
RIP: 0010:sysfs_remove_file_ns+0x27/0x70 fs/sysfs/file.c:468
Code: 00 00 00 41 54 55 48 89 fd 53 49 89 d4 48 89 f3 e8 ee 76 9c ff 48 8d 7d 30 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 <80> 3c 02 00 75 2d 48 89 da 48 b8 00 00 00 00 00 fc ff df 48 8b 6d
RSP: 0018:ffff8881e9d9fc00 EFLAGS: 00010206
RAX: dffffc0000000000 RBX: ffffffff900367e0 RCX: ffffffff81a95952
RDX: 0000000000000006 RSI: ffffc90001405000 RDI: 0000000000000030
RBP: 0000000000000000 R08: fffffbfff1fa22ed R09: fffffbfff1fa22ed
R10: 0000000000000001 R11: fffffbfff1fa22ec R12: 0000000000000000
R13: ffffffffc1abdac0 R14: 1ffff1103d3b3f8b R15: 0000000000000000
FS:  00007fe409dc1700(0000) GS:ffff8881f1200000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000001b2d721000 CR3: 00000001e98b6005 CR4: 00000000007606f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
PKRU: 55555554
Call Trace:
 sysfs_remove_file include/linux/sysfs.h:519 [inline]
 driver_remove_file+0x40/0x50 drivers/base/driver.c:122
 pcmcia_remove_newid_file drivers/pcmcia/ds.c:163 [inline]
 pcmcia_unregister_driver+0x7d/0x2b0 drivers/pcmcia/ds.c:209
 ssb_modexit+0xa/0x1b [ssb]
 __do_sys_delete_module kernel/module.c:1018 [inline]
 __se_sys_delete_module kernel/module.c:961 [inline]
 __x64_sys_delete_module+0x3dc/0x5e0 kernel/module.c:961
 do_syscall_64+0x147/0x600 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x462e99
Code: f7 d8 64 89 02 b8 ff ff ff ff c3 66 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 bc ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fe409dc0c58 EFLAGS: 00000246 ORIG_RAX: 00000000000000b0
RAX: ffffffffffffffda RBX: 000000000073bf00 RCX: 0000000000462e99
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 00000000200000c0
RBP: 0000000000000002 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007fe409dc16bc
R13: 00000000004bccaa R14: 00000000006f6bc8 R15: 00000000ffffffff
Modules linked in: ssb(-) 3c59x nvme_core macvlan tap pata_hpt3x3 rt2x00pci null_blk tsc40 pm_notifier_error_inject notifier_error_inject mdio cdc_wdm nf_reject_ipv4 ath9k_common ath9k_hw ath pppox ppp_generic slhc ehci_platform wl12xx wlcore tps6507x_ts ioc4 nf_synproxy_core ide_gd_mod ax25 can_dev iwlwifi can_raw atm tm2_touchkey can_gw can sundance adp5588_keys rt2800mmio rt2800lib rt2x00mmio rt2x00lib eeprom_93cx6 pn533 lru_cache elants_i2c ip_set nfnetlink gameport tipc hampshire nhc_ipv6 nhc_hop nhc_udp nhc_fragment nhc_routing nhc_mobility nhc_dest 6lowpan silead brcmutil nfc mt76_usb mt76 mac80211 iptable_security iptable_raw iptable_mangle iptable_nat nf_nat_ipv4 nf_nat nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 iptable_filter bpfilter ip6_vti ip_gre sit hsr veth vxcan batman_adv cfg80211 rfkill chnl_net caif nlmon vcan bridge stp llc ip6_gre ip6_tunnel tunnel6 tun joydev mousedev serio_raw ide_pci_generic piix floppy ide_core sch_fq_codel ip_tables x_tables ipv6
 [last unloaded: 3c59x]
Dumping ftrace buffer:
   (ftrace buffer empty)
---[ end trace 3913cbf8011e1c05 ]---

In ssb_modinit, it does not fail SSB init when ssb_host_pcmcia_init failed,
however in ssb_modexit, ssb_host_pcmcia_exit calls pcmcia_unregister_driver
unconditionally, which may tigger a NULL pointer dereference issue as above.

Reported-by: Hulk Robot <hulkci@huawei.com>
Fixes: 399500da18f7 ("ssb: pick PCMCIA host code support from b43 driver")
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>