linux-kernel - Re: [PATCH 1/3] uml: drivers/net

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Date:	Fri, 8 Jul 2011 13:30:56 +0300
From:	Vitaliy Ivanov <vitalivanov@...il.com>
To:	Richard Weinberger <richard@....at>
Cc:	Jeff Dike <jdike@...toit.com>,
	user-mode-linux-devel@...ts.sourceforge.net,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/3] uml: drivers/net_user.c memory leak fix

On Thu, Jul 7, 2011 at 8:27 PM, Richard Weinberger <richard@....at> wrote:
> Am Donnerstag 07 Juli 2011, 18:36:02 schrieb Vitaliy Ivanov:
>> >From 9b9f36f46aa708c3245f5ded83f96421966b2edf Mon Sep 17 00:00:00 2001
>>
>> From: Vitaliy Ivanov <vitalivanov@...il.com>
>> Date: Thu, 7 Jul 2011 19:23:13 +0300
>> Subject: [PATCH 1/3] uml: drivers/net_user.c memory leak fix
>>
>> Perform memory cleanup on exit.
>> On receiving invalid 'pid' we still should clean 'output' variable.
>>
>> Signed-off-by: Vitaliy Ivanov <vitalivanov@...il.com>
>> ---
>>  arch/um/drivers/net_user.c |    5 +++--
>>  1 files changed, 3 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/um/drivers/net_user.c b/arch/um/drivers/net_user.c
>> index 9415dd9..989b653 100644
>> --- a/arch/um/drivers/net_user.c
>> +++ b/arch/um/drivers/net_user.c
>> @@ -228,10 +228,11 @@ static void change(char *dev, char *what, unsigned
>> char *addr, "buffer\n");
>>
>>       pid = change_tramp(argv, output, output_len);
>> -     if (pid < 0) return;
>>
>>       if (output != NULL) {
>> -             printk("%s", output);
>> +             if (pid >= 0) {
>> +                     printk("%s", output);
>> +             }
>>               kfree(output);
>>       }
>>  }
>
> This control logic is a bit strange.
> When change_tramp() fails we should not printk() the output variable.
>
> if (pid < 0){
>  free(output);
>  return;
> }
>
> Would be much cleaner.

I just didn't want to clone this free-return stuff. So, what you
proposing is like this:
------------
...
        output = uml_kmalloc(output_len, UM_GFP_KERNEL);
        if (output == NULL)
                printk(UM_KERN_ERR "change : failed to allocate output "
                       "buffer\n");

        pid = change_tramp(argv, output, output_len);
        if (pid < 0) {
                free(output);               <---------- I'm not sure
but 'output' can be NULL here.
                return;
        }

        if (output != NULL) {
                printk("%s", output);
                kfree(output);
        }
}
------------

I was trying to print 'output' only in case change_tramp is
successful. That's the old logic. And at the same time perform free
only in case output is not NULL.


Vitaliy
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