From patchwork Mon Feb 18 23:23:08 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: 10818953 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 86EC71399 for ; Mon, 18 Feb 2019 23:25:08 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 710292BD84 for ; Mon, 18 Feb 2019 23:25:08 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 53ED22BE65; Mon, 18 Feb 2019 23:25:08 +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 722AD2BD84 for ; Mon, 18 Feb 2019 23:25:07 +0000 (UTC) Received: (qmail 30045 invoked by uid 550); 18 Feb 2019 23:24:34 -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 29951 invoked from network); 18 Feb 2019 23:24:33 -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=GesfR975C7GXSJuXJWymo3Fhv9NK44xbOlcyXlyCbOk=; b=xgx287FH AMLAl4CUQUxjIcz2psOOAw5omubl//MhTw4uG6dJGsqEV++XoO6ZP9YSlUGXEt16 B20pUZ3ZoDcpEW28JWWFmCK/wH7y7STITc0PEfViZ631UsTh/+PmzHPiYEZgtWjJ iUiYh8mW2KvNtmqs4Ib03TEwQH+CFpPadEoGuFCIU0igdLBcHmBKkthFyLd+EBIZ ukQKC3xEfWHeX6QB/AUw7XgC8snS94pWkBaRvi6N2q/9wpBn0I/q8BtNiYtD8/hP b3xjdYD8kCkw86ATJndWaIUYd31HzQ9Z9Brsr7MhDwgIzf6KLsaWeTRGLokr3h1M W3E8LwgW8zE9wA== X-ME-Sender: X-ME-Proxy-Cause: gggruggvucftvghtrhhoucdtuddrgedutddrtddvgddtjeculddtuddrgedtledrtddtmd cutefuodetggdotefrodftvfcurfhrohhfihhlvgemucfhrghsthforghilhdpqfhuthen uceurghilhhouhhtmecufedttdenucesvcftvggtihhpihgvnhhtshculddquddttddmne cujfgurhephffvufffkffojghfggfgsedtkeertdertddtnecuhfhrohhmpedfvfhosghi nhcuvedrucfjrghrughinhhgfdcuoehtohgsihhnsehkvghrnhgvlhdrohhrgheqnecukf hppeduvddurdeggedrvddtvddrudeftdenucfrrghrrghmpehmrghilhhfrhhomhepthho sghinheskhgvrhhnvghlrdhorhhgnecuvehluhhsthgvrhfuihiivgeptd X-ME-Proxy: From: "Tobin C. Harding" To: Kees Cook Cc: "Tobin C. Harding" , Shuah Khan , Alexander Shishkin , Greg Kroah-Hartman , Andy Shevchenko , kernel-hardening@lists.openwall.com, linux-kernel@vger.kernel.org Subject: [PATCH 6/6] lib: Add function strscpy_from_user() Date: Tue, 19 Feb 2019 10:23:08 +1100 Message-Id: <20190218232308.11241-7-tobin@kernel.org> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20190218232308.11241-1-tobin@kernel.org> References: <20190218232308.11241-1-tobin@kernel.org> MIME-Version: 1.0 X-Virus-Scanned: ClamAV using ClamSMTP Currently we have strncpy_from_userspace(). If the user string is longer than the destination kernel buffer we get an error code -EFAULT. We are unable to recover from here because this is the same error returned if the access to userspace fails totally. There is no reason we cannot continue execution with the user string truncated. Add a function strscpy_from_user() that guarantees the string written is null-terminated. If user string is longer than destination buffer truncates the string. Returns the number of characters written excluding the null-terminator. Signed-off-by: Tobin C. Harding --- lib/strncpy_from_user.c | 43 +++++++++++++++++++++++++++++++++++++++++ 1 file changed, 43 insertions(+) diff --git a/lib/strncpy_from_user.c b/lib/strncpy_from_user.c index 11fe9a4a00fd..6bd603ccec7a 100644 --- a/lib/strncpy_from_user.c +++ b/lib/strncpy_from_user.c @@ -120,3 +120,46 @@ long strncpy_from_user(char *dst, const char __user *src, long count) return -EFAULT; } EXPORT_SYMBOL(strncpy_from_user); + +/** + * strscpy_from_user() - Copy a NUL terminated string from userspace. + * @dst: Destination address, in kernel space. This buffer must be at + * least @count bytes long. + * @src: Source address, in user space. + * @count: Maximum number of bytes to copy, including the trailing %NUL. + * + * Copies a NUL-terminated string from userspace to kernel space. When + * the function returns @dst is guaranteed to be null terminated. + * + * Return: If access to userspace fails, returns -EFAULT. Otherwise, + * return the number of characters copied excluding the trailing + * %NUL. + */ +long strscpy_from_user(char *dst, const char __user *src, long count) +{ + unsigned long max_addr, src_addr; + + if (unlikely(count <= 0)) + return 0; + + max_addr = user_addr_max(); + src_addr = (unsigned long)src; + if (likely(src_addr < max_addr)) { + unsigned long max = max_addr - src_addr; + long retval; + + kasan_check_write(dst, count); + check_object_size(dst, count, false); + if (user_access_begin(src, max)) { + retval = do_strncpy_from_user(dst, src, count, max); + user_access_end(); + if (retval == -EFAULT) { + dst[count-1] = '\0'; + return count - 1; + } + return retval; + } + } + return -EFAULT; +} +EXPORT_SYMBOL(strscpy_from_user);