linux-kernel - Re: [kernel-hardening] [PATCH] move RLIMIT_NPROC check from set_user() to do_execve

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Message-ID: <20110725234013.GB24110@openwall.com>
Date:	Tue, 26 Jul 2011 03:40:13 +0400
From:	Solar Designer <solar@...nwall.com>
To:	Vasiliy Kulikov <segoon@...nwall.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	NeilBrown <neilb@...e.de>, Stephen Smalley <sds@...ho.nsa.gov>,
	kernel-hardening@...ts.openwall.com,
	James Morris <jmorris@...ei.org>, linux-kernel@...r.kernel.org,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"David S. Miller" <davem@...emloft.net>,
	Jiri Slaby <jslaby@...e.cz>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	linux-fsdevel@...r.kernel.org,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Eric Paris <eparis@...hat.com>, Willy Tarreau <w@....eu>,
	Sebastian Krahmer <krahmer@...e.de>
Subject: Re: [kernel-hardening] [PATCH] move RLIMIT_NPROC check from set_user() to do_execve_common()

Vasiliy,

On Mon, Jul 25, 2011 at 09:14:23PM +0400, Vasiliy Kulikov wrote:
> @@ -1433,6 +1433,19 @@ static int do_execve_common(const char *filename,
>  	struct files_struct *displaced;
>  	bool clear_in_exec;
>  	int retval;
> +	const struct cred *cred = current_cred();
> +
> +	/*
> +	 * We move the actual failure in case of RLIMIT_NPROC excess from
> +	 * set*uid() to execve() because too many poorly written programs
> +	 * don't check setuid() return code.  Here we additionally recheck
> +	 * whether NPROC limit is still exceeded.
> +	 */
> +	if ((current->flags & PF_NPROC_EXCEEDED) &&
> +	    atomic_read(&cred->user->processes) > rlimit(RLIMIT_NPROC)) {
> +		retval = -EAGAIN;
> +		goto out_ret;
> +	}

Do you possibly need:

	current->flags &= ~PF_NPROC_EXCEEDED;

somewhere after this point?

I think it's weird to have past set_user() failure affect other than the
very next execve().

Perhaps also reset the flag on fork() because we have an RLIMIT_NPROC
check on fork() anyway.

Thanks,

Alexander
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