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

From: Solar Designer <solar@openwall.com>
To: Vasiliy Kulikov <segoon@openwall.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
	NeilBrown <neilb@suse.de>, Stephen Smalley <sds@tycho.nsa.gov>,
	kernel-hardening@lists.openwall.com,
	James Morris <jmorris@namei.org>,
	linux-kernel@vger.kernel.org, Greg Kroah-Hartman <gregkh@suse.de>,
	Andrew Morton <akpm@linux-foundation.org>,
	"David S. Miller" <davem@davemloft.net>,
	Jiri Slaby <jslaby@suse.cz>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	linux-fsdevel@vger.kernel.org,
	KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
	Eric Paris <eparis@redhat.com>, Willy Tarreau <w@1wt.eu>,
	Sebastian Krahmer <krahmer@suse.de>
Subject: Re: [kernel-hardening] [PATCH] move RLIMIT_NPROC check from set_user() to do_execve_common()
Date: Tue, 26 Jul 2011 03:40:13 +0400	[thread overview]
Message-ID: <20110725234013.GB24110@openwall.com> (raw)
In-Reply-To: <20110725171423.GA3739@albatros>

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