linux-kernel - Re: [PATCH v2 8/8] FS: proc, make limits writable

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Date:	Mon, 12 Oct 2009 17:13:55 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Jiri Slaby <jirislaby@...il.com>
Cc:	akpm@...ux-foundation.org, mingo@...hat.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 8/8] FS: proc, make limits writable

On 10/08, Jiri Slaby wrote:
>
> On 09/04/2009 04:26 PM, Oleg Nesterov wrote:
> > One small nit, just to suggest the further 9/8 cleanup,
> >
> >> +static const struct file_operations proc_pid_limits_operations = {
> >> +	.read		= proc_info_read,
> >> +	.write		= limits_write,
> >> +};
> >
> > I think it makes sense to tweak proc_pid_limits() a little bit (and
> > rename it), so that we can do
> >
> > 	.read = limits_read,
> > 	.write = limits_write
> >
> > Then,
> >
> >> @@ -2501,7 +2571,9 @@ static const struct pid_entry tgid_base_stuff[] = {
> >> +	NOD("limits",	  S_IFREG|S_IRUSR|S_IWUSR, NULL,
> >> +			&proc_pid_limits_operations,
> >> +			{ .proc_read = proc_pid_limits }),
> >
> > We could use
> >
> > 	REG("limits", S_IRUSR|S_IWUSR, &proc_pid_limits_operations),
> >
> > instead, this looks a bit cleaner to me.
>
> Hi again, nobody picked them up yet, I waited till the end of the merge
> window and now I'll repost.
>
> Did you mean here to do the proc_info_read work (get/put task, alloc
> buf, simple_read) directly in limits_read?

limits_read() has to do get_proc_task(d_inode), yes. Otherwise I don't
see any additional complications, you can use simple_read_from_buffer(),
no need to allocate the buffer but of course you can you shouldn't
write more than "size_t count" bytes.

But perhaps I missed something, and in any case this is up to you. If
you don't like this - please forget.

> > And another minor nit (just in case you will re-submit this series for
> > some reason). Perhaps the changelog in 6/8 should mention that we do
> > not do any security checks when tsk != current (without selinux). We
> > assume that either the caller is sys_setrlimit(), or the caller should
> > verify it has rights to change the limits: in case of limits_write()
> > we rely on ->mode = S_IRUSR|S_IWUSR.
>
> I did it as a comment by the setrlimit. I think nobody would care about
> a changelog note ;).

Good ;)

Oleg.

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