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

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Date:   Wed, 31 Jul 2019 18:47:35 +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 2019-07-24 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.

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)).