usb: typec: tcpm: Add NULL check before dereferencing config

commit 1957de95 upstream.

When instantiating tcpm on an NXP OM 13588 board with NXP PTN5110,
the following crash is seen when writing into the 'preferred_role'
sysfs attribute.

Unable to handle kernel NULL pointer dereference at virtual address 00000028
pgd = f69149ad
[00000028] *pgd=00000000
Internal error: Oops: 5 [#1] THUMB2
Modules linked in: tcpci tcpm
CPU: 0 PID: 1882 Comm: bash Not tainted 5.1.18-sama5-armv7-r2 #4
Hardware name: Atmel SAMA5
PC is at tcpm_try_role+0x3a/0x4c [tcpm]
LR is at tcpm_try_role+0x15/0x4c [tcpm]
pc : [<bf8000e2>]    lr : [<bf8000bd>]    psr: 60030033
sp : dc1a1e88  ip : c03fb47d  fp : 00000000
r10: dc216190  r9 : dc1a1f78  r8 : 00000001
r7 : df4ae044  r6 : dd032e90  r5 : dd1ce340  r4 : df4ae054
r3 : 00000000  r2 : 00000000  r1 : 00000000  r0 : df4ae044
Flags: nZCv  IRQs on  FIQs on  Mode SVC_32  ISA Thumb  Segment none
Control: 50c53c7d  Table: 3efec059  DAC: 00000051
Process bash (pid: 1882, stack limit = 0x6a6d4aa5)
Stack: (0xdc1a1e88 to 0xdc1a2000)
1e80:                   dd05d808 dd1ce340 00000001 00000007 dd1ce340 c03fb4a7
1ea0: 00000007 00000007 dc216180 00000000 00000000 c01e1e03 00000000 00000000
1ec0: c0907008 dee98b40 c01e1d5d c06106c4 00000000 00000000 00000007 c0194e8b
1ee0: 0000000a 00000400 00000000 c01a97db dc22bf00 ffffe000 df4b6a00 df745900
1f00: 00000001 00000001 000000dd c01a9c2f 7aeab3be c0907008 00000000 dc22bf00
1f20: c0907008 00000000 00000000 00000000 00000000 7aeab3be 00000007 dee98b40
1f40: 005dc318 dc1a1f78 00000000 00000000 00000007 c01969f7 0000000a c01a20cb
1f60: dee98b40 c0907008 dee98b40 005dc318 00000000 c0196b9b 00000000 00000000
1f80: dee98b40 7aeab3be 00000074 005dc318 b6f3bdb0 00000004 c0101224 dc1a0000
1fa0: 00000004 c0101001 00000074 005dc318 00000001 005dc318 00000007 00000000
1fc0: 00000074 005dc318 b6f3bdb0 00000004 00000007 00000007 00000000 00000000
1fe0: 00000004 be800880 b6ed35b3 b6e5c746 60030030 00000001 00000000 00000000
[<bf8000e2>] (tcpm_try_role [tcpm]) from [<c03fb4a7>] (preferred_role_store+0x2b/0x5c)
[<c03fb4a7>] (preferred_role_store) from [<c01e1e03>] (kernfs_fop_write+0xa7/0x150)
[<c01e1e03>] (kernfs_fop_write) from [<c0194e8b>] (__vfs_write+0x1f/0x104)
[<c0194e8b>] (__vfs_write) from [<c01969f7>] (vfs_write+0x6b/0x104)
[<c01969f7>] (vfs_write) from [<c0196b9b>] (ksys_write+0x43/0x94)
[<c0196b9b>] (ksys_write) from [<c0101001>] (ret_fast_syscall+0x1/0x62)

Since commit 96232cbc ("usb: typec: tcpm: support get typec and pd
config from device properties"), the 'config' pointer in struct tcpc_dev
is optional when registering a Type-C port. Since it is optional, we have
to check if it is NULL before dereferencing it.

Reported-by: Douglas Gilbert <dgilbert@interlog.com>
Cc: Douglas Gilbert <dgilbert@interlog.com>
Fixes: 96232cbc ("usb: typec: tcpm: support get typec and pd config from device properties")
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Cc: stable <stable@vger.kernel.org>
Reviewed-by: Jun Li <jun.li@nxp.com>
Reviewed-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Link: https://lore.kernel.org/r/1563979112-22483-1-git-send-email-linux@roeck-us.net


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>