Re: [PATCH v6] Added PR_SET_PROCTITLE_AREA option for prctl()

[Ingo Molnar <mingo@elte.hu>]

* KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> wrote:

> +	/*
> +	 * If argv and environ aren't continuous (i.e. the process used
> +	 * prctl(PR_SET_PROCTITLE_AREA)), we don't care environ override.

s/dont't care environ override/don't care about the evironment override/

> +		case PR_SET_PROCTITLE_AREA: {
> +			struct mm_struct *mm = current->mm;
> +			unsigned long addr = arg2;
> +			unsigned long len = arg3;
> +			unsigned long end = arg2 + arg3;

would be cleaner to write the latter as 'addr + len'.

> +			if (len > PAGE_SIZE)
> +				return -EINVAL;
> +
> +			if (addr >= end)
> +				return -EINVAL;
> +
> +			/*
> +			 * If the process pass broken pointer, EFAULT is might better
> +			 * than ps output zero-length proctitle. Plus if
> +			 * the process pass kernel address (or something-else),
> +			 * We have to block it. Oherwise, strange exploit
> +			 * chance is there.
> +			 */
> +			if (!access_ok(VERIFY_READ, addr, len))
> +				return -EFAULT;

the addr >= end check looks (partly) duplicative of the access_ok() 
check.

> +
> +			down_write(&mm->mmap_sem);
> +			mm->arg_start = addr;
> +			mm->arg_end = end;
> +			up_write(&mm->mmap_sem);

well we might as well name 'addr' as 'start' and have a match then here 
too.

The feature looks useful, but the choice of a prctl as an API is strange 
- it limits us to the current task only - while the ability to set 
arguments for another task looks a more generic (and potentially more 
useful) solution.

	Ingo