From patchwork Sun Nov 12 09:18:05 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Alejandro Colomar X-Patchwork-Id: 79627 Return-Path: X-Original-To: patchwork@sourceware.org Delivered-To: patchwork@sourceware.org Received: from server2.sourceware.org (localhost [IPv6:::1]) by sourceware.org (Postfix) with ESMTP id BD5A93858291 for ; Sun, 12 Nov 2023 09:18:25 +0000 (GMT) X-Original-To: libc-alpha@sourceware.org Delivered-To: libc-alpha@sourceware.org Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by sourceware.org (Postfix) with ESMTPS id 0E58F3858C33 for ; Sun, 12 Nov 2023 09:18:11 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.2 sourceware.org 0E58F3858C33 Authentication-Results: sourceware.org; dmarc=pass (p=none dis=none) header.from=kernel.org Authentication-Results: sourceware.org; spf=pass smtp.mailfrom=kernel.org ARC-Filter: OpenARC Filter v1.0.0 sourceware.org 0E58F3858C33 Authentication-Results: server2.sourceware.org; arc=none smtp.remote-ip=2604:1380:4641:c500::1 ARC-Seal: i=1; a=rsa-sha256; d=sourceware.org; s=key; t=1699780692; cv=none; b=KzArope+1TYNaLZYO7F+JuKpOrvvh1sExM0UWPjIVSRpJWp2VUQTkGiTReHUL5W6YUDBayWjbSFNXKc2Qfz0wvC40cJDCCLm8m/oxhpCHsQyG8ykxkwqUE64JjGigAWg9VEFmzP9K6F46mYrSgEkZ5b4gb/4+zfGO4I7a+CUnSI= ARC-Message-Signature: i=1; a=rsa-sha256; d=sourceware.org; s=key; t=1699780692; c=relaxed/simple; bh=4hFvmgBEONg7cOZD8NWcY4fX/eld8CvY7FFyB612+wc=; h=DKIM-Signature:Date:From:To:Subject:Message-ID:MIME-Version; b=Aj+Vb2zs4uYMGc0JKOavypuPz3Zer9Yi+DgbbAwf/zxp8BopUZfrWN92+RrBO4x2JzQOWwRSI7SVyrjtVkBIEoql6uYXA9er9Qc55JOjPkCYhRJ52zoXrIEZ4wYape+UUViGngBFF+ewl1SZx7sCvURjoD0fZOdjdxsPLmwLYGs= ARC-Authentication-Results: i=1; server2.sourceware.org Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by dfw.source.kernel.org (Postfix) with ESMTP id A552260BD6; Sun, 12 Nov 2023 09:18:10 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 458FDC433C7; Sun, 12 Nov 2023 09:18:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1699780690; bh=4hFvmgBEONg7cOZD8NWcY4fX/eld8CvY7FFyB612+wc=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=hsIi/sSU0g5qFCK5zpFu45JWRF98KMSDuG+k8Vt4J0hgnJaFU6SfjB2fue6ds8fv5 ymHp5ePuHoI2h7lpNLz2Mmn+7TQmQXPKJqAzAhEJbW9G99gs6HFOnwl1zjFgD8lrTL 2hKCfMVxW9bEN4THu8saTA0VSJ8dJQzx4ZON0pvfOY5dMUvfWt5J/pJfD4A39tnzyI 2jsJMmZx0S9vu62bkV+Ckn/QdFnfvqhzWixZtfFx2d9spmWd0nss4FsB20ubKre9Go LjwnonlDi+B92ngv6Pg+k/VUwnUmnTzDMIZdIxfqZo+rwTDQ+cx30f5CqAErlSzEKs wG6ZP5Xc3wjFA== Date: Sun, 12 Nov 2023 10:18:05 +0100 From: Alejandro Colomar To: linux-man@vger.kernel.org Cc: Alejandro Colomar , libc-alpha@sourceware.org, Paul Eggert , Jonny Grant , DJ Delorie , Matthew House , Oskari Pirhonen , Thorsten Kukuk , Adhemerval Zanella Netto , Zack Weinberg , "G. Branden Robinson" , Carlos O'Donell , Xi Ruoyao , Stefan Puiu , Andreas Schwab Subject: [PATCH 2/2] string_copying.7: BUGS: Document strl{cpy,cat}(3)'s performance problems Message-ID: <20231112091748.6906-4-alx@kernel.org> References: MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: X-Mailer: git-send-email 2.42.0 X-Spam-Status: No, score=-9.5 required=5.0 tests=BAYES_00, DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, GIT_PATCH_0, KAM_ASCII_DIVIDERS, SPF_HELO_NONE, SPF_PASS, TXREP, T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org X-BeenThere: libc-alpha@sourceware.org X-Mailman-Version: 2.1.30 Precedence: list List-Id: Libc-alpha mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: libc-alpha-bounces+patchwork=sourceware.org@sourceware.org Also point to BUGS from other sections that talk about these functions. These functions are doomed due to the design decision of mirroring snprintf(3)'s return value. They must return strlen(src), which makes them terribly slow, and vulnerable to DoS if an attacker can control strlen(src). A better design would have been to return -1 when truncating. Reported-by: Paul Eggert Cc: Jonny Grant Cc: DJ Delorie Cc: Matthew House Cc: Oskari Pirhonen Cc: Thorsten Kukuk Cc: Adhemerval Zanella Netto Cc: Zack Weinberg Cc: "G. Branden Robinson" Cc: Carlos O'Donell Cc: Xi Ruoyao Cc: Stefan Puiu Cc: Andreas Schwab Signed-off-by: Alejandro Colomar --- man7/string_copying.7 | 18 +++++++++++++++++- 1 file changed, 17 insertions(+), 1 deletion(-) diff --git a/man7/string_copying.7 b/man7/string_copying.7 index 0254fbba6..cb3910db0 100644 --- a/man7/string_copying.7 +++ b/man7/string_copying.7 @@ -226,9 +226,9 @@ .SS Truncate or not? .IP \[bu] .BR strlcpy (3bsd) and .BR strlcat (3bsd) -are similar, but less efficient when chained. +are similar, but have important performance problems; see BUGS. .IP \[bu] .BR stpncpy (3) and .BR strncpy (3) @@ -417,8 +417,10 @@ .SS Functions the resulting string is truncated (but it is guaranteed to be null-terminated). They return the length of the total string they tried to create. .IP +Check BUGS before using these functions. +.IP .BR stpecpy (3) is a simpler alternative to these functions. .\" ----- DESCRIPTION :: Functions :: stpncpy(3) ----------------------/ .TP @@ -598,8 +600,22 @@ .SH BUGS into normal copy functions, since .I strlen(dst) is usually a byproduct of the previous copy. +.P +.BR strlcpy (3) +and +.BR strlcat (3) +need to read the entire +.I src +string, +even if the destination buffer is small. +This makes them vulnerable to Denial of Service (DoS) attacks +if an attacker can control the length of the +.I src +string. +And if not, +they're still unnecessarily slow. .\" ----- EXAMPLES :: -------------------------------------------------/ .SH EXAMPLES The following are examples of correct use of each of these functions. .\" ----- EXAMPLES :: stpcpy(3) ---------------------------------------/