From patchwork Wed Mar 6 21:42:25 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Tobin C. Harding" X-Patchwork-Id: 10841833 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id E64F3922 for ; Wed, 6 Mar 2019 21:44:16 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id D65E828E59 for ; Wed, 6 Mar 2019 21:44:16 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id C9C572DF2C; Wed, 6 Mar 2019 21:44:16 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.2 required=2.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,MAILING_LIST_MULTI,RCVD_IN_DNSWL_MED autolearn=ham version=3.3.1 Received: from mother.openwall.net (mother.openwall.net [195.42.179.200]) by mail.wl.linuxfoundation.org (Postfix) with SMTP id B23C728E59 for ; Wed, 6 Mar 2019 21:44:15 +0000 (UTC) Received: (qmail 9795 invoked by uid 550); 6 Mar 2019 21:43:50 -0000 Mailing-List: contact kernel-hardening-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Delivered-To: mailing list kernel-hardening@lists.openwall.com Received: (qmail 9711 invoked from network); 6 Mar 2019 21:43:49 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d= messagingengine.com; h=cc:content-transfer-encoding:date:from :in-reply-to:message-id:mime-version:references:subject:to :x-me-proxy:x-me-proxy:x-me-sender:x-me-sender:x-sasl-enc; s= fm2; bh=/nV4R65tDruN/v686WfRixCHJzIvFZo2KvdAUUUu1dk=; b=5OtGZGAB WsqVoXcmrnh6BKuzGnwKlhU4S2XSTVJph8MsUMc+o3c8o06lAUl5mkNgqO5Ou9pv 8apDP9RZOlDaDuIq/320o1mk7ZsLN00v3VJPsIcs8uYdNOO1qiT2VHmSYicXX17G 94ck4kvxMsX/RI7eK/cqselA2O/6pMwvejAkMXO5lMLfMweXuxRjWiZifrZK9jxs 0kDZEuq58ZxhgLlkU9KkP/+Ixm8OquQ/2V8fsgCoPNpyR/M6bnxdqEDHEG0otXLG hzoApEA6OG/2bsZ1Tv3XnwA0ihOZg8q/s6h1skhcaCw1L5dTz7M3/kzd/Ow1RGfY ECuZzFZrbvX5kg== X-ME-Sender: X-ME-Proxy-Cause: gggruggvucftvghtrhhoucdtuddrgedutddrfeeigdekjecutefuodetggdotefrodftvf curfhrohhfihhlvgemucfhrghsthforghilhdpqfgfvfdpuffrtefokffrpgfnqfghnecu uegrihhlohhuthemuceftddtnecusecvtfgvtghiphhivghnthhsucdlqddutddtmdenuc fjughrpefhvffufffkofgjfhgggfestdekredtredttdenucfhrhhomhepfdfvohgsihhn ucevrdcujfgrrhguihhnghdfuceothhosghinheskhgvrhhnvghlrdhorhhgqeenucfkph epuddvgedrudeiledrhedrudehkeenucfrrghrrghmpehmrghilhhfrhhomhepthhosghi nheskhgvrhhnvghlrdhorhhgnecuvehluhhsthgvrhfuihiivgephe X-ME-Proxy: From: "Tobin C. Harding" To: Kees Cook , Shuah Khan Cc: "Tobin C. Harding" , Jann Horn , Andy Shevchenko , Randy Dunlap , Rasmus Villemoes , Stephen Rothwell , Andy Lutomirski , Daniel Micay , Arnd Bergmann , Miguel Ojeda , "Gustavo A. R. Silva" , Greg Kroah-Hartman , Alexander Shishkin , kernel-hardening@lists.openwall.com, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH v3 6/7] lib/string: Add strscpy_pad() function Date: Thu, 7 Mar 2019 08:42:25 +1100 Message-Id: <20190306214226.14598-7-tobin@kernel.org> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20190306214226.14598-1-tobin@kernel.org> References: <20190306214226.14598-1-tobin@kernel.org> MIME-Version: 1.0 X-Virus-Scanned: ClamAV using ClamSMTP We have a function to copy strings safely and we have a function to copy strings and zero the tail of the destination (if source string is shorter than destination buffer) but we do not have a function to do both at once. This means developers must write this themselves if they desire this functionality. This is a chore, and also leaves us open to off by one errors unnecessarily. Add a function that calls strscpy() then memset()s the tail to zero if the source string is shorter than the destination buffer. Signed-off-by: Tobin C. Harding Acked-by: Kees Cook --- include/linux/string.h | 4 ++++ lib/string.c | 47 +++++++++++++++++++++++++++++++++++------- 2 files changed, 44 insertions(+), 7 deletions(-) diff --git a/include/linux/string.h b/include/linux/string.h index 7927b875f80c..bfe95bf5d07e 100644 --- a/include/linux/string.h +++ b/include/linux/string.h @@ -31,6 +31,10 @@ size_t strlcpy(char *, const char *, size_t); #ifndef __HAVE_ARCH_STRSCPY ssize_t strscpy(char *, const char *, size_t); #endif + +/* Wraps calls to strscpy()/memset(), no arch specific code required */ +ssize_t strscpy_pad(char *dest, const char *src, size_t count); + #ifndef __HAVE_ARCH_STRCAT extern char * strcat(char *, const char *); #endif diff --git a/lib/string.c b/lib/string.c index 38e4ca08e757..3a3353512184 100644 --- a/lib/string.c +++ b/lib/string.c @@ -159,11 +159,9 @@ EXPORT_SYMBOL(strlcpy); * @src: Where to copy the string from * @count: Size of destination buffer * - * Copy the string, or as much of it as fits, into the dest buffer. - * The routine returns the number of characters copied (not including - * the trailing NUL) or -E2BIG if the destination buffer wasn't big enough. - * The behavior is undefined if the string buffers overlap. - * The destination buffer is always NUL terminated, unless it's zero-sized. + * Copy the string, or as much of it as fits, into the dest buffer. The + * behavior is undefined if the string buffers overlap. The destination + * buffer is always NUL terminated, unless it's zero-sized. * * Preferred to strlcpy() since the API doesn't require reading memory * from the src string beyond the specified "count" bytes, and since @@ -173,8 +171,10 @@ EXPORT_SYMBOL(strlcpy); * * Preferred to strncpy() since it always returns a valid string, and * doesn't unnecessarily force the tail of the destination buffer to be - * zeroed. If the zeroing is desired, it's likely cleaner to use strscpy() - * with an overflow test, then just memset() the tail of the dest buffer. + * zeroed. If zeroing is desired please use strscpy_pad(). + * + * Return: The number of characters copied (not including the trailing + * %NUL) or -E2BIG if the destination buffer wasn't big enough. */ ssize_t strscpy(char *dest, const char *src, size_t count) { @@ -237,6 +237,39 @@ ssize_t strscpy(char *dest, const char *src, size_t count) EXPORT_SYMBOL(strscpy); #endif +/** + * strscpy_pad() - Copy a C-string into a sized buffer + * @dest: Where to copy the string to + * @src: Where to copy the string from + * @count: Size of destination buffer + * + * Copy the string, or as much of it as fits, into the dest buffer. The + * behavior is undefined if the string buffers overlap. The destination + * buffer is always %NUL terminated, unless it's zero-sized. + * + * If the source string is shorter than the destination buffer, zeros + * the tail of the destination buffer. + * + * For full explanation of why you may want to consider using the + * 'strscpy' functions please see the function docstring for strscpy(). + * + * Return: The number of characters copied (not including the trailing + * %NUL) or -E2BIG if the destination buffer wasn't big enough. + */ +ssize_t strscpy_pad(char *dest, const char *src, size_t count) +{ + ssize_t written; + + written = strscpy(dest, src, count); + if (written < 0 || written == count - 1) + return written; + + memset(dest + written + 1, 0, count - written - 1); + + return written; +} +EXPORT_SYMBOL(strscpy_pad); + #ifndef __HAVE_ARCH_STRCAT /** * strcat - Append one %NUL-terminated string to another