linux-kernel - Re: [PATCH v2] usb: typec: tcpm: Add NULL check before dereferencing config

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Message-ID: <a4bd4df7-a16c-3002-e42c-066406cab3bd@interlog.com>
Date:   Thu, 1 Aug 2019 13:26:41 +0200
From:   Douglas Gilbert <dgilbert@...erlog.com>
To:     Guenter Roeck <linux@...ck-us.net>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] usb: typec: tcpm: Add NULL check before dereferencing
 config

On 2019-07-31 6:47 p.m., Douglas Gilbert wrote:
> On 2019-07-24 4:38 p.m., Guenter Roeck wrote:
>> 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 96232cbc6c994 ("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@...erlog.com>
>> Cc: Douglas Gilbert <dgilbert@...erlog.com>
>> Fixes: 96232cbc6c994 ("usb: typec: tcpm: support get typec and pd config from 
>> device properties")
>> Signed-off-by: Guenter Roeck <linux@...ck-us.net>
>> ---
>> v2: Added missing Cc:. Sorry for the noise.
>>
>> Doug:
>>      I didn't add your Tested-by: since I added more code.
>>      It would be great if you can re-test.
>>
>>   drivers/usb/typec/tcpm/tcpm.c | 7 ++++---
>>   1 file changed, 4 insertions(+), 3 deletions(-)
> 
> Tested-by: Douglas Gilbert <dgilbert@...erlog.com>
> 
> 
> This time the Linux system is an Acme Systems Arietta which is a
> Atmel at91sam9g25 based board. Test was run with lk 5.1.19 .
> Without the patch I got the oops described above ("PC is at
> tcpm_try_role+0x40/0x74 [tcpm]") when writing into the 'preferred_role'
> sysfs attribute. With this patch it worked okay.

Today I tried this patch on lk 5.2.5 with the same hardware and it
worked, as expected.

Doug Gilbert

> Can't test the "out of protocol" PD Attention command oops because I
> don't have another OM13588 at the other end (of the USB-C cable) to
> send it. I may be able to solve that problem as well. The OM13588
> seems like a good attack vector ... and NXP continue to improve
> its software (I'm talking about when it runs with a KL27Z which is
> an Arduino clone). It can now read the current capability of an
> E-marked USB-C (M to M) cable. The only 5 Amp cable I have is
> the one that Apple sells (as an _extra_ (cheapskates) to their 87W
> USB-C power adapter (for MacBooks)).