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 24984C433EF for ; Fri, 27 May 2022 11:47:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1351665AbiE0LrQ (ORCPT ); Fri, 27 May 2022 07:47:16 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55476 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1351989AbiE0LpN (ORCPT ); Fri, 27 May 2022 07:45:13 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2F61713C361; Fri, 27 May 2022 04:41:40 -0700 (PDT) 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 9BCAD61CE7; Fri, 27 May 2022 11:41:39 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id A9E41C34113; Fri, 27 May 2022 11:41:38 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1653651699; bh=hZxyEAMbBobh8dF4JKUDHBDC9LPGBRyQuIRVk05DggI=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Dbs5vTX4+ch1f9o93wCcZCCxVn4+1ne+iUGeXALGO8yJnCcsuQqIqGTqNbhp//A// zhYxI7LII9at5XZ4hJcx6cxQAizOgwDRVqxdbZHYizJ/fNKalX78ZywEM/5Kx9ibp8 9NhwMd+KwM+0Ktcu0/XinvlfKS/kU7VOw905lGws= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Linus Torvalds , Jann Horn , "Jason A. Donenfeld" Subject: [PATCH 5.17 064/111] random: allow partial reads if later user copies fail Date: Fri, 27 May 2022 10:49:36 +0200 Message-Id: <20220527084828.597913681@linuxfoundation.org> X-Mailer: git-send-email 2.36.1 In-Reply-To: <20220527084819.133490171@linuxfoundation.org> References: <20220527084819.133490171@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: "Jason A. Donenfeld" commit 5209aed5137880fa229746cb521f715e55596460 upstream. Rather than failing entirely if a copy_to_user() fails at some point, instead we should return a partial read for the amount that succeeded prior, unless none succeeded at all, in which case we return -EFAULT as before. This makes it consistent with other reader interfaces. For example, the following snippet for /dev/zero outputs "4" followed by "1": int fd; void *x = mmap(NULL, 4096, PROT_WRITE, MAP_ANONYMOUS | MAP_PRIVATE, -1, 0); assert(x != MAP_FAILED); fd = open("/dev/zero", O_RDONLY); assert(fd >= 0); printf("%zd\n", read(fd, x, 4)); printf("%zd\n", read(fd, x + 4095, 4)); close(fd); This brings that same standard behavior to the various RNG reader interfaces. While we're at it, we can streamline the loop logic a little bit. Suggested-by: Linus Torvalds Cc: Jann Horn Signed-off-by: Jason A. Donenfeld Signed-off-by: Greg Kroah-Hartman --- drivers/char/random.c | 22 ++++++++++++---------- 1 file changed, 12 insertions(+), 10 deletions(-) --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -523,8 +523,7 @@ EXPORT_SYMBOL(get_random_bytes); static ssize_t get_random_bytes_user(void __user *buf, size_t nbytes) { - ssize_t ret = 0; - size_t len; + size_t len, left, ret = 0; u32 chacha_state[CHACHA_STATE_WORDS]; u8 output[CHACHA_BLOCK_SIZE]; @@ -543,37 +542,40 @@ static ssize_t get_random_bytes_user(voi * the user directly. */ if (nbytes <= CHACHA_KEY_SIZE) { - ret = copy_to_user(buf, &chacha_state[4], nbytes) ? -EFAULT : nbytes; + ret = nbytes - copy_to_user(buf, &chacha_state[4], nbytes); goto out_zero_chacha; } - do { + for (;;) { chacha20_block(chacha_state, output); if (unlikely(chacha_state[12] == 0)) ++chacha_state[13]; len = min_t(size_t, nbytes, CHACHA_BLOCK_SIZE); - if (copy_to_user(buf, output, len)) { - ret = -EFAULT; + left = copy_to_user(buf, output, len); + if (left) { + ret += len - left; break; } - nbytes -= len; buf += len; ret += len; + nbytes -= len; + if (!nbytes) + break; BUILD_BUG_ON(PAGE_SIZE % CHACHA_BLOCK_SIZE != 0); - if (!(ret % PAGE_SIZE) && nbytes) { + if (ret % PAGE_SIZE == 0) { if (signal_pending(current)) break; cond_resched(); } - } while (nbytes); + } memzero_explicit(output, sizeof(output)); out_zero_chacha: memzero_explicit(chacha_state, sizeof(chacha_state)); - return ret; + return ret ? ret : -EFAULT; } /*