linux-kernel - Re: [PATCH v2] s390/raw3270: Handle memory allocation failures in raw3270_setup

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Date: Tue, 25 Jun 2024 16:44:47 +0900
From: Yunseong Kim <yskelg@...il.com>
To: Heiko Carstens <hca@...ux.ibm.com>
Cc: Harald Freudenberger <freude@...ux.ibm.com>,
 Vasily Gorbik <gor@...ux.ibm.com>, Alexander Gordeev
 <agordeev@...ux.ibm.com>, Christian Borntraeger <borntraeger@...ux.ibm.com>,
 Sven Schnelle <svens@...ux.ibm.com>, Markus Elfring <Markus.Elfring@....de>,
 MichelleJin <shjy180909@...il.com>, linux-s390@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] s390/raw3270: Handle memory allocation failures in
 raw3270_setup_console()

Hi Heiko,

On 6/25/24 3:31 오후, Heiko Carstens wrote:
> On Tue, Jun 25, 2024 at 10:32:26AM +0900, yskelg@...il.com wrote:
>> From: Yunseong Kim <yskelg@...il.com>
>>
>> A null pointer is stored in a local variable after a call of the function
>> "kzalloc" failed. This pointer was passed to a subsequent call of the
>> function "raw3270_setup_device" where an undesirable dereference will be
>> performed then. Thus add corresponding return value checks.
>> The allocated each memory areas are immediately overwritten by the called
>> function zero-initialisation be omitted by calling the "kmalloc" instead.
>> After "ccw_device_enable_console" succeeds, set the bit raw3270 flag to
>> RAW3270_FLAGS_CONSOLE.
>>
>> Fixes: 33403dcfcdfd ("[S390] 3270 console: convert from bootmem to slab")
>> Cc: linux-s390@...r.kernel.org
>> Signed-off-by: Yunseong Kim <yskelg@...il.com>
>> ---
>>  drivers/s390/char/raw3270.c | 20 +++++++++++++++-----
>>  1 file changed, 15 insertions(+), 5 deletions(-)
> ...
>>  	rc = raw3270_setup_device(cdev, rp, ascebc);
>> -	if (rc)
>> +	if (rc) {
>> +		kfree(ascebc);
>> +		kfree(rp);
>>  		return ERR_PTR(rc);
>> -	set_bit(RAW3270_FLAGS_CONSOLE, &rp->flags);
>> -
>> +	}
>>  	rc = ccw_device_enable_console(cdev);
>>  	if (rc) {
>>  		ccw_device_destroy_console(cdev);
>> +		kfree(ascebc);
>> +		kfree(rp);
>>  		return ERR_PTR(rc);
>>  	}
>> +	set_bit(RAW3270_FLAGS_CONSOLE, &rp->flags);
> 
> Why did you move the set_bit() call?

Thank you for the code review Heiko.

While writing patch version 2, I spent a lot of time thinking about this
part. Previously, even if function "ccw_device_enable_console" failed,
the flag was set to RAW3270_FLAGS_CONSOLE and returned.

I think it would be more appropriate to set the bit after everything
succeeded, so I included and submitted this code in v2 patch.

I’d appreciate hearing your thoughts on this!


Warm regards,

Yunseong Kim