Re: [PATCH] /proc/*/environ: wrong placing of ptrace_may_attach() check

[Andrew Morton <akpm@linux-foundation.org>]

On Mon, 28 May 2007 17:41:57 +0400
Alexey Dobriyan <adobriyan@sw.ru> wrote:

> Signed-off-by: Alexey Dobriyan <adobriyan@sw.ru>

Better changelogs, please.

> --- a/fs/proc/base.c
> +++ b/fs/proc/base.c
> @@ -204,12 +204,17 @@ static int proc_pid_environ(struct task_
>  	int res = 0;
>  	struct mm_struct *mm = get_task_mm(task);
>  	if (mm) {
> -		unsigned int len = mm->env_end - mm->env_start;
> +		unsigned int len;
> +
> +		res = -ESRCH;
> +		if (!ptrace_may_attach(task))
> +			goto out;
> +
> +		len  = mm->env_end - mm->env_start;
>  		if (len > PAGE_SIZE)
>  			len = PAGE_SIZE;
>  		res = access_process_vm(task, mm->env_start, buffer, len, 0);
> -		if (!ptrace_may_attach(task))
> -			res = -ESRCH;
> +out:
>  		mmput(mm);
>  	}
>  	return res;

What's wrong with the existing code?  It's a bit dopey-looking and can, I
guess, permit a task to cause a pagefault in an mm which it doesn't have
permission to read from.  But is there some more serious problem being
fixed here?

I shouldn't have to ask this stuff.