linux-kernel - Re: [PATCH 1/1] USB: serial/usb_wwan, fix tty NULL dereference

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Date:	Tue, 15 Feb 2011 19:36:28 +0100
From:	Jiri Slaby <jirislaby@...il.com>
To:	Amit Shah <amitshah@....net>
CC:	Sergei Shtylyov <sshtylyov@...sta.com>,
	Jiri Slaby <jslaby@...e.cz>, gregkh@...e.de,
	linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] USB: serial/usb_wwan, fix tty NULL dereference

On 02/15/2011 07:10 PM, Amit Shah wrote:
> On (Tue) 15 Feb 2011 [20:14:50], Sergei Shtylyov wrote:
>> Hello.
>>
>> Jiri Slaby wrote:
>>
>>> tty_port_tty_get may return without any problems NULL. Handle this
>>> case and do not oops in usb_wwan_indat_callback by dereferencing it.
> 
> Thanks for looking at this!
> 
>>> The oops:
>>> Unable to handle kernel paging request for data at address 0x000000d8
>>> Faulting instruction address: 0xc0175b3c
>>> Oops: Kernel access of bad area, sig: 11 [#1]
>>> PowerPC 40x Platform
>>> last sysfs file:
>>> /sys/devices/pci0000:00/0000:00:00.0/0000:01:00.0/0000:02:09.2/usb1/idVendor
>>> Modules linked in:
>>> NIP: c0175b3c LR: c0175e7c CTR: c0215c90
>>> REGS: c77f7d50 TRAP: 0300   Not tainted  (2.6.37-rc5)
>>> MSR: 00021030 <ME,CE,IR,DR>  CR: 88482028  XER: 2000005f
>>> DEAR: 000000d8, ESR: 00000000
>>> TASK = c7141b90[1149] 'wvdial' THREAD: c2750000
>>> GPR00: 00021030 c77f7e00 c7141b90 00000000 0000000e 00000000 0000000e c0410680
>>> GPR08: c683db00 00000000 00000001 c03c81f8 88482028 10073ef4 ffffffb9 ffffff94
>>> GPR16: 00000000 fde036c0 00200200 00100100 00000001 ffffff8d c34fabcc 00000000
>>> GPR24: c71120d4 00000000 00000000 0000000e 00021030 00000000 00000000 0000000e
>>> NIP [c0175b3c] tty_buffer_request_room+0x2c/0x194
>>> LR [c0175e7c] tty_insert_flip_string_fixed_flag+0x3c/0xb0
>>> Call Trace:
>>> [c77f7e00] [00000003] 0x3 (unreliable)
>>> [c77f7e30] [c0175e7c] tty_insert_flip_string_fixed_flag+0x3c/0xb0
>>> [c77f7e60] [c0215df4] usb_wwan_indat_callback+0x164/0x170
>>> ...
>>
>>> References: https://bugzilla.kernel.org/show_bug.cgi?id=24582
>>> Cc: Amit Shah <amitshah@....net>
>>> Cc: baoyb <baoyb@...t.org.cn>
>>> Cc: Greg Kroah-Hartman <gregkh@...e.de>
>>> Signed-off-by: Jiri Slaby <jslaby@...e.cz>
>>> ---
>>> drivers/usb/serial/usb_wwan.c |   15 +++++++++------
>>> 1 files changed, 9 insertions(+), 6 deletions(-)
>>
>>> diff --git a/drivers/usb/serial/usb_wwan.c b/drivers/usb/serial/usb_wwan.c
>>> index b004b2a..9c014e2 100644
>>> --- a/drivers/usb/serial/usb_wwan.c
>>> +++ b/drivers/usb/serial/usb_wwan.c
>>> @@ -295,12 +295,15 @@ static void usb_wwan_indat_callback(struct urb *urb)
>>> 		    __func__, status, endpoint);
>>> 	} else {
>>> 		tty = tty_port_tty_get(&port->port);
>>> -		if (urb->actual_length) {
>>> -			tty_insert_flip_string(tty, data, urb->actual_length);
>>> -			tty_flip_buffer_push(tty);
>>> -		} else
>>> -			dbg("%s: empty read urb received", __func__);
>>> -		tty_kref_put(tty);
>>> +		if (tty) {
>>> +			if (urb->actual_length) {
>>> +				tty_insert_flip_string(tty, data,
>>> +						urb->actual_length);
>>> +				tty_flip_buffer_push(tty);
>>> +			} else
>>> +				dbg("%s: empty read urb received", __func__);
>>
>>    Should be {} on the *else* branch too, according to Documentation/CodingStyle...
> 
> If you're fixing that, might as well return in the 'if' above

No, the urb has to be resubmitted.

regards,
-- 
js
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