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

[Solar Designer <solar@openwall.com>]

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