Subject: Re: [patch] isdn: make sure strings are null terminated

From: walter harms <[email-masked]>
Date: Thu, 24 Nov 2011 13:21:42 +0100

Am 24.11.2011 12:34, schrieb Dan Carpenter:
> On Wed, Nov 23, 2011 at 09:25:56AM +0100, walter harms wrote:
>>
>>
>> Am 23.11.2011 07:42, schrieb Dan Carpenter:
>>> These strings come from the user.  We strcpy() them inside
>>> cf_command() so we should check that they are NULL terminated and
>>> return an error if not.
>>>
>>> Signed-off-by: Dan Carpenter <[email-masked]>
>>>
>>> diff --git a/drivers/isdn/divert/divert_procfs.c b/drivers/isdn/divert/divert_procfs.c
>>> index 33ec9e4..0c16687 100644
>>> --- a/drivers/isdn/divert/divert_procfs.c
>>> +++ b/drivers/isdn/divert/divert_procfs.c
>>> @@ -242,6 +242,10 @@ static int isdn_divert_ioctl_unlocked(struct file *file, uint cmd, ulong arg)
>>>  		case IIOCDOCFINT:
>>>  			if (!divert_if.drv_to_name(dioctl.cf_ctrl.drvid))
>>>  				return (-EINVAL);	/* invalid driver */
>>> +			if (strlen(dioctl.cf_ctrl.msn) >= sizeof(dioctl.cf_ctrl.msn))
>>> +				return -EINVAL;
>>> +			if (strlen(dioctl.cf_ctrl.fwd_nr) >= sizeof(dioctl.cf_ctrl.fwd_nr))
>>> +				return -EINVAL;
>>
>> forcing the last field to be zero seems more easy.
>> dioctl.cf_ctrl.fwd_nr[sizeof(dioctl.cf_ctrl.fwd_nr))-1]=0;
>>
> 
> That's a valid option to use, but I'd prefer to return an error code
> here because that's what we do on the line before.  Passing a too
> long string is clearly invalid.
> 

the line before has the same problem, of cause.

So far i see you do not get a string, you get a structure. An it will hard
to validate the element is a useful string. I thing my (sledgehammer) method
is ok here because you make sure that all later calls (strcmp,strcpy) will succeed.
If someone supplies a bad string the later calls will catch by failing to identify
and return a proper code from there (at least i hope so).

re,
 wh