From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Google-Smtp-Source: AG47ELuhFJ9rbxLMbZLYsge5fNs8dr8uY/c4SQlGeHoq9FBR66w5dwn9aNH6MpCggCJWCLyZ1/Jv ARC-Seal: i=1; a=rsa-sha256; t=1520479936; cv=none; d=google.com; s=arc-20160816; b=TJ7LyYFcyMUTl292yeFYn4TTSzBvMzmI1gAiFjHw1mEL5BTK0lwQz1T1NVCn7Eeqf3 ahD0wAs9GoIw7QE9Dr/PO5hG7GcxE/J+QIp0C8Vevy338j4u1mcpIi7jhf+RGyFXCZ3s LuqOeKZ3pK1pKQt8yUWAaFd6nTqBSuBeJGOJeK4uUJK68bwaH4Fo/1d16ShIvnh2GpwN NG2+wPraGPnqW1IMQdoGaMpRFUBDD7sbHU1Q/DyBfFX0mVm2ggm8w+VJPiabqA9mYCen 3XHJE2nihdl3OJGrcTAIhvHXAyjvR8XGDSJwLgBY461V5AqnY5oKsAxZmQRrHtAYGswJ vNGA== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=references:in-reply-to:message-id:date:subject:cc:to:from :dkim-signature:delivered-to:list-id:list-subscribe:list-unsubscribe :list-help:list-post:precedence:mailing-list :arc-authentication-results; bh=RNDM7GZdsDPxYnFcKPqvjTjxnD8widEXNa1zIpYjArk=; b=gSisNR04tztTLtCaJoTmJBcYuTxXibOhvH8AUkqeZF9WfiU9UU3J4GuAhnJXR6lZL2 3s0ItFLhTOQOVbi7SYgxvAZesDV+NIpR0KT9FIYxZr5YCY8gPzbBeqLJnGAQZ/6xfWr2 ZQWxWpvWe5GMqEVS5aRHfhiMxwtDLP4MliRRDJnJbfAe51LOFK4Xgl/P2LNaacOLGI0D 8nJRWwYP836MCxxQV6cNkqPWvwzIPJWzTXXUwT5hBi+7Z2hVHUxR9bXpCiF1Dig+ya/P LI+GrXWwq5myjunuM/6TN+/OLO0qWIegQ9dJ4w/r3jyzvDNHY9SseSvCXQ5w+Uw2MXFO oHgg== ARC-Authentication-Results: i=1; mx.google.com; dkim=pass header.i=@chromium.org header.s=google header.b=eCIUkMuB; spf=pass (google.com: domain of kernel-hardening-return-12228-gregkh=linuxfoundation.org@lists.openwall.com designates 195.42.179.200 as permitted sender) smtp.mailfrom=kernel-hardening-return-12228-gregkh=linuxfoundation.org@lists.openwall.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=chromium.org Authentication-Results: mx.google.com; dkim=pass header.i=@chromium.org header.s=google header.b=eCIUkMuB; spf=pass (google.com: domain of kernel-hardening-return-12228-gregkh=linuxfoundation.org@lists.openwall.com designates 195.42.179.200 as permitted sender) smtp.mailfrom=kernel-hardening-return-12228-gregkh=linuxfoundation.org@lists.openwall.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=chromium.org Mailing-List: contact kernel-hardening-help@lists.openwall.com; run by ezmlm List-Post: List-Help: List-Unsubscribe: List-Subscribe: From: Kees Cook To: Andrew Morton Cc: Kees Cook , linux-kernel@vger.kernel.org, corbet@lwn.net, gustavo@embeddedor.com, rostedt@goodmis.org, Chris Mason , Josef Bacik , David Sterba , "David S. Miller" , Alexey Kuznetsov , Hideaki YOSHIFUJI , Ingo Molnar , Peter Zijlstra , Thomas Gleixner , Masahiro Yamada , Borislav Petkov , Josh Poimboeuf , Randy Dunlap , Ian Abbott , "Tobin C. Harding" , Sergey Senozhatsky , Petr Mladek , Andy Shevchenko , Pantelis Antoniou , linux-btrfs@vger.kernel.org, netdev@vger.kernel.org, kernel-hardening@lists.openwall.com Subject: [PATCH v2 1/3] vsprintf: Remove accidental VLA usage Date: Wed, 7 Mar 2018 19:30:45 -0800 Message-Id: <1520479847-39174-2-git-send-email-keescook@chromium.org> X-Mailer: git-send-email 2.7.4 In-Reply-To: <1520479847-39174-1-git-send-email-keescook@chromium.org> References: <1520479847-39174-1-git-send-email-keescook@chromium.org> X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: =?utf-8?q?1594322119542311159?= X-GMAIL-MSGID: =?utf-8?q?1594338769399316188?= X-Mailing-List: linux-kernel@vger.kernel.org List-ID: In the quest to remove all stack VLAs from the kernel[1], this introduces a new "simple max" macro, and changes the "sym" array size calculation to use it. The value is actually a fixed size, but since the max() macro uses some extensive tricks for safety, it ends up looking like a variable size to the compiler. [1] https://lkml.org/lkml/2018/3/7/621 Signed-off-by: Kees Cook --- include/linux/kernel.h | 11 +++++++++++ lib/vsprintf.c | 4 ++-- 2 files changed, 13 insertions(+), 2 deletions(-) diff --git a/include/linux/kernel.h b/include/linux/kernel.h index 3fd291503576..1da554e9997f 100644 --- a/include/linux/kernel.h +++ b/include/linux/kernel.h @@ -820,6 +820,17 @@ static inline void ftrace_dump(enum ftrace_dump_mode oops_dump_mode) { } x, y) /** + * SIMPLE_MAX - return maximum of two values without any type checking + * @x: first value + * @y: second value + * + * This should only be used in stack array sizes, since the type-checking + * from max() confuses the compiler into thinking a VLA is being used. + */ +#define SIMPLE_MAX(x, y) ((size_t)(x) > (size_t)(y) ? (size_t)(x) \ + : (size_t)(y)) + +/** * min3 - return minimum of three values * @x: first value * @y: second value diff --git a/lib/vsprintf.c b/lib/vsprintf.c index d7a708f82559..50cce36e1cdc 100644 --- a/lib/vsprintf.c +++ b/lib/vsprintf.c @@ -744,8 +744,8 @@ char *resource_string(char *buf, char *end, struct resource *res, #define FLAG_BUF_SIZE (2 * sizeof(res->flags)) #define DECODED_BUF_SIZE sizeof("[mem - 64bit pref window disabled]") #define RAW_BUF_SIZE sizeof("[mem - flags 0x]") - char sym[max(2*RSRC_BUF_SIZE + DECODED_BUF_SIZE, - 2*RSRC_BUF_SIZE + FLAG_BUF_SIZE + RAW_BUF_SIZE)]; + char sym[SIMPLE_MAX(2*RSRC_BUF_SIZE + DECODED_BUF_SIZE, + 2*RSRC_BUF_SIZE + FLAG_BUF_SIZE + RAW_BUF_SIZE)]; char *p = sym, *pend = sym + sizeof(sym); int decode = (fmt[0] == 'R') ? 1 : 0; -- 2.7.4