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 X-Spam-Level: X-Spam-Status: No, score=-16.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9DE86C48BE8 for ; Tue, 15 Jun 2021 15:51:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 820D961476 for ; Tue, 15 Jun 2021 15:51:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232520AbhFOPx4 (ORCPT ); Tue, 15 Jun 2021 11:53:56 -0400 Received: from foss.arm.com ([217.140.110.172]:39096 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232373AbhFOPwY (ORCPT ); Tue, 15 Jun 2021 11:52:24 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 4390E143B; Tue, 15 Jun 2021 08:50:19 -0700 (PDT) Received: from entos-ampere-02.shanghai.arm.com (entos-ampere-02.shanghai.arm.com [10.169.214.103]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id 98EE73F694; Tue, 15 Jun 2021 08:50:14 -0700 (PDT) From: Jia He To: Petr Mladek , Steven Rostedt , Sergey Senozhatsky , Andy Shevchenko , Rasmus Villemoes , Jonathan Corbet , Alexander Viro , Linus Torvalds Cc: "Peter Zijlstra (Intel)" , Eric Biggers , "Ahmed S. Darwish" , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, Matthew Wilcox , Jia He Subject: [PATCH RFCv4 3/4] lib/test_printf.c: split write-beyond-buffer check in two Date: Tue, 15 Jun 2021 23:49:51 +0800 Message-Id: <20210615154952.2744-4-justin.he@arm.com> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20210615154952.2744-1-justin.he@arm.com> References: <20210615154952.2744-1-justin.he@arm.com> Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org From: Rasmus Villemoes Before each invocation of vsnprintf(), do_test() memsets the entire allocated buffer to a sentinel value. That buffer includes leading and trailing padding which is never included in the buffer area handed to vsnprintf (spaces merely for clarity): pad test_buffer pad **** **************** **** Then vsnprintf() is invoked with a bufsize argument <= BUF_SIZE. Suppose bufsize=10, then we'd have e.g. |pad | test_buffer |pad | **** pizza0 **** ****** **** A B C D E where vsnprintf() was given the area from B to D. It is obviously a bug for vsnprintf to touch anything between A and B or between D and E. The former is checked for as one would expect. But for the latter, we are actually a little stricter in that we check the area between C and E. Split that check in two, providing a clearer error message in case it was a genuine buffer overrun and not merely a write within the provided buffer, but after the end of the generated string. So far, no part of the vsnprintf() implementation has had any use for using the whole buffer as scratch space, but it's not unreasonable to allow that, as long as the result is properly nul-terminated and the return value is the right one. However, it is somewhat unusual, and most % won't need this, so keep the [C,D] check, but make it easy for a later patch to make that part opt-out for certain tests. Signed-off-by: Rasmus Villemoes Tested-by: Jia He Signed-off-by: Jia He --- lib/test_printf.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/lib/test_printf.c b/lib/test_printf.c index ec0d5976bb69..d1d2f898ebae 100644 --- a/lib/test_printf.c +++ b/lib/test_printf.c @@ -78,12 +78,17 @@ do_test(int bufsize, const char *expect, int elen, return 1; } - if (memchr_inv(test_buffer + written + 1, FILL_CHAR, BUF_SIZE + PAD_SIZE - (written + 1))) { + if (memchr_inv(test_buffer + written + 1, FILL_CHAR, bufsize - (written + 1))) { pr_warn("vsnprintf(buf, %d, \"%s\", ...) wrote beyond the nul-terminator\n", bufsize, fmt); return 1; } + if (memchr_inv(test_buffer + bufsize, FILL_CHAR, BUF_SIZE + PAD_SIZE - bufsize)) { + pr_warn("vsnprintf(buf, %d, \"%s\", ...) wrote beyond buffer\n", bufsize, fmt); + return 1; + } + if (memcmp(test_buffer, expect, written)) { pr_warn("vsnprintf(buf, %d, \"%s\", ...) wrote '%s', expected '%.*s'\n", bufsize, fmt, test_buffer, written, expect); -- 2.17.1