From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 16F81C4332F for ; Sat, 19 Nov 2022 20:40:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234931AbiKSUkS (ORCPT ); Sat, 19 Nov 2022 15:40:18 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45744 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233485AbiKSUja (ORCPT ); Sat, 19 Nov 2022 15:39:30 -0500 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 773DB12D1D; Sat, 19 Nov 2022 12:39:29 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id E03D060BBA; Sat, 19 Nov 2022 20:39:28 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 00685C433C1; Sat, 19 Nov 2022 20:39:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1668890368; bh=+YFG65zK+ig5GsbiwocxVDqflXqp3NTQLYHgrK//RV8=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=uI4+VOv5qj+YubiO/jBt2kpkGPiwzDuZXWyX1lVzq5T2ysdrmunWaK02PLLSWIgRG M47WLr0UdxMFYuXmyDwngVF+Phrm/0ZdX3dg41OetTY7MItuKSsQtPmm6Cz9IWE8oT MoiUrwYCfmAID9ZDP0Th8pSfbDLelCTy3o3Da8H8xut8FadG0eSgNIx4W7EjnkOZNv Gnev27yrn4U/QBmY5ZkFHBHVT5xHFjL0fJD0sFY9662vC4VJT6x6dr0rIc1l1filVK 1oTat6Hu/bG4ifVPxw+MUsZrQZGiKxXLXty1xoC8cKql0V22PnrqKaCyvdkM2H7asG CAcUrFa/7TvQA== Date: Sat, 19 Nov 2022 12:39:26 -0800 From: Eric Biggers To: "Jason A. Donenfeld" Cc: linux-kernel@vger.kernel.org, patches@lists.linux.dev, linux-crypto@vger.kernel.org, x86@kernel.org, Thomas Gleixner , Greg Kroah-Hartman , Adhemerval Zanella Netto , Carlos O'Donell Subject: Re: [PATCH v5 1/3] random: add vgetrandom_alloc() syscall Message-ID: References: <20221119120929.2963813-1-Jason@zx2c4.com> <20221119120929.2963813-2-Jason@zx2c4.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20221119120929.2963813-2-Jason@zx2c4.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Nov 19, 2022 at 01:09:27PM +0100, Jason A. Donenfeld wrote: > +SYSCALL_DEFINE3(vgetrandom_alloc, unsigned long __user *, num, > + unsigned long __user *, size_per_each, unsigned int, flags) > +{ > + unsigned long alloc_size; > + unsigned long num_states; > + unsigned long pages_addr; > + int ret; > + > + if (flags) > + return -EINVAL; > + > + if (get_user(num_states, num)) > + return -EFAULT; > + > + alloc_size = size_mul(num_states, sizeof(struct vgetrandom_state)); > + if (alloc_size == SIZE_MAX) > + return -EOVERFLOW; > + alloc_size = roundup(alloc_size, PAGE_SIZE); Small detail: the roundup to PAGE_SIZE can make alloc_size overflow to 0. Also, 'roundup(alloc_size, PAGE_SIZE)' could be 'PAGE_ALIGN(alloc_size)'. > + pages_addr = vm_mmap(NULL, 0, alloc_size, PROT_READ | PROT_WRITE, > + MAP_PRIVATE | MAP_ANONYMOUS | MAP_LOCKED, 0); > + if (IS_ERR_VALUE(pages_addr)) > + return pages_addr; This will only succeed if the userspace process has permission to mlock pages, i.e. if there is space available in RLIMIT_MEMLOCK or if process has CAP_IPC_LOCK. I suppose this is working as intended, as this syscall can be used to try to allocate and mlock arbitrary amounts of memory. I wonder if this permission check will cause problems. Maybe there could be a way to relax it for just one page per task? I don't know how that would work, though, especially when the planned usage involves userspace allocating a single pool of these contexts per process that get handed out to threads. - Eric