linux-kernel - Re: [PATCH] s390: net: claw.c: Fix a define larger than in a sizeof in conjunction with strncpy

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Date:	Wed, 30 Jul 2014 21:54:59 +0200
From:	Rickard Strandqvist <rickard_strandqvist@...ctrumdigital.se>
To:	Ursula Braun <ubraun@...ux.vnet.ibm.com>
Cc:	Ursula Braun <ursula.braun@...ibm.com>,
	Frank Blaschka <blaschka@...ux.vnet.ibm.com>,
	linux390@...ibm.com, Martin Schwidefsky <schwidefsky@...ibm.com>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	linux-s390@...r.kernel.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] s390: net: claw.c: Fix a define larger than in a sizeof
 in conjunction with strncpy

2014-07-30 10:10 GMT+02:00 Ursula Braun <ubraun@...ux.vnet.ibm.com>:
> On Sun, 2014-07-27 at 13:50 +0200, Rickard Strandqvist wrote:
>> The MAX_NAME_LEN is larger than sizeof, which could potentially
>> giving lots of error here.
>>
>> Signed-off-by: Rickard Strandqvist <rickard_strandqvist@...ctrumdigital.se>
>> ---
>>  drivers/s390/net/claw.c |   31 +++++++++++++++++++------------
>>  1 file changed, 19 insertions(+), 12 deletions(-)
>>
>> diff --git a/drivers/s390/net/claw.c b/drivers/s390/net/claw.c
>> index d837c3c..0172ce8 100644
>> --- a/drivers/s390/net/claw.c
>> +++ b/drivers/s390/net/claw.c
>> @@ -3068,12 +3068,15 @@ claw_hname_write(struct device *dev, struct device_attribute *attr,
>>       if (!priv)
>>               return -ENODEV;
>>       p_env = priv->p_env;
>> -     if (count > MAX_NAME_LEN+1)
>> +     if (count >= sizeof(p_env->host_name) && count > 0)
>>               return -EINVAL;
>> -     memset(p_env->host_name, 0x20, MAX_NAME_LEN);
>> +
>>       strncpy(p_env->host_name,buf, count);
>> -     p_env->host_name[count-1] = 0x20;  /* clear extra 0x0a */
>> -     p_env->host_name[MAX_NAME_LEN] = 0x00;
>> +     /* clear extra 0x0a */
>> +     memset(&p_env->host_name[count - 1],
>> +                     ' ', sizeof(p_env->host_name) - count);
>> +     p_env->host_name[sizeof(p_env->host_name) - 1] = '\0';
>> +
>>       CLAW_DBF_TEXT(2, setup, "HstnSet");
>>       CLAW_DBF_TEXT_(2, setup, "%s", p_env->host_name);
>>
>> @@ -3106,12 +3109,14 @@ claw_adname_write(struct device *dev, struct device_attribute *attr,
>>       if (!priv)
>>               return -ENODEV;
>>       p_env = priv->p_env;
>> -     if (count > MAX_NAME_LEN+1)
>> +     if (count >= sizeof(p_env->adapter_name) && count > 0)
>>               return -EINVAL;
>> -     memset(p_env->adapter_name, 0x20, MAX_NAME_LEN);
>> +
>>       strncpy(p_env->adapter_name,buf, count);
>> -     p_env->adapter_name[count-1] = 0x20; /* clear extra 0x0a */
>> -     p_env->adapter_name[MAX_NAME_LEN] = 0x00;
>> +     /* clear extra 0x0a */
>> +     memset(&p_env->adapter_name[count - 1],
>> +                     ' ', sizeof(p_env->adapter_name) - count);
>> +     p_env->adapter_name[sizeof(p_env->adapter_name) - 1] = '\0';
>>       CLAW_DBF_TEXT(2, setup, "AdnSet");
>>       CLAW_DBF_TEXT_(2, setup, "%s", p_env->adapter_name);
>>
>> @@ -3145,12 +3150,14 @@ claw_apname_write(struct device *dev, struct device_attribute *attr,
>>       if (!priv)
>>               return -ENODEV;
>>       p_env = priv->p_env;
>> -     if (count > MAX_NAME_LEN+1)
>> +     if (count >= sizeof(p_env->api_type) && count > 0)
>>               return -EINVAL;
>> -     memset(p_env->api_type, 0x20, MAX_NAME_LEN);
>> +
>>       strncpy(p_env->api_type,buf, count);
>> -     p_env->api_type[count-1] = 0x20;  /* we get a loose 0x0a */
>> -     p_env->api_type[MAX_NAME_LEN] = 0x00;
>> +     /* we get a loose 0x0a */
>> +     memset(&p_env->api_type[count - 1],
>> +                     ' ', sizeof(p_env->api_type) - count);
>> +     p_env->api_type[sizeof(p_env->api_type) - 1] = '\0';
>>       if(strncmp(p_env->api_type,WS_APPL_NAME_PACKED,6) == 0) {
>>               p_env->read_size=DEF_PACK_BUFSIZE;
>>               p_env->write_size=DEF_PACK_BUFSIZE;
>
> Why do you say "MAX_NAME_LEN is larger than sizeof"? MAX_NAME_LEN is 8,
> and claw_env has defined its char arrays as ...[9]?
>

Hi Ursula!

Wondering how I was thinking there. No, no error there.
Possible I assumed that MAX_NAME_LEN it was actually used in the
struct definition, and that was wrong then.
It's something I otherwise think would have been reasonable to do!

And the error I see in the current code is.
It will be wrong if the count == 0 or count == MAX_NAME_LEN + 1 is wrong.

Do not know what you think in general about my patch, or if you want
to keep it more as before.
Otherwise, I have come up with one that is both clearer and better looking...

New patch on the way!  :)

Kind regards
Rickard Strandqvist
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