From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Google-Smtp-Source: AH8x226xK4Tp09pirWr4wS3nJb1bdBEN+nIEkG4/XA0vHAAMglKsOzC9ZezLGZDC98m9KcHUHmxd ARC-Seal: i=1; a=rsa-sha256; t=1518062833; cv=none; d=google.com; s=arc-20160816; b=BHsjY6SJEx1xsykRSGmuQb59frSh3f1sysfL1DODKk/fs+b0bGUjMbDd+1PxCHJtyo gSIJ6pUH9e1btRNvvMm3B3H4CsoFs5UR7RzR4dzf2DSbEy4kDjTmcIreZ6mWY5PoRta6 eaDDuSmytSRyFjB9DgQqH6FF/Xv3lklV5rgv/7Fy0MgC5K6xgeXaaQKT2njSOAow0u4V D2PbmLW7rgaMTtWFUk2h05gSFCONnGiIWo28Cpblc9F/S8dBWcJC4v7bgf3XXg0XA7le C62ZyvdbXifvnno3VFKXGJlb6fWm1V5ujM/2dl5QbCrb0TIWKAvwTHLhMCd91O7J2kO7 zQjA== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=user-agent:in-reply-to:content-disposition:mime-version:references :message-id:subject:cc:to:from:date:dkim-signature:delivered-to :list-id:list-subscribe:list-unsubscribe:list-help:list-post :precedence:mailing-list:arc-authentication-results; bh=R9nnssFPF9ywdef9ImzpTBWz7oMqSHut8meIUnwwVTM=; b=LzYeRm3M61pRWF5my3/xKqKBNIFiNttyFlR4QZzgq7v1suDCs3gZUiOOcZHG7rTJuu nQDRTooC4vJSFcodfK4SC17vhmQ7Q681qn6QvM3CTadEkK+Wdyn08AiYjJq+/AqkIL4I tKLdt4S1FuMI8W6J2gR52nAUN9cXBWXkU9zHVxJJB5xwV31TpI2nByyeslVif+5C1MJM soAIzqmPJaki4xBxIz5TCH9vLX0GjDnE0ctOu6sICxTw+bM7f/Xyc68j3kckgFd2mL2v h1UCKjKKIprzJ/jQuxT3ObxHN+ODQGPombN9Zg2ZR4F0Ir4LQvNb53J4ZzKS+RFWVq6o ZooA== ARC-Authentication-Results: i=1; mx.google.com; dkim=fail header.i=@infradead.org header.s=bombadil.20170209 header.b=che3nTqo; spf=pass (google.com: domain of kernel-hardening-return-11656-gregkh=linuxfoundation.org@lists.openwall.com designates 195.42.179.200 as permitted sender) smtp.mailfrom=kernel-hardening-return-11656-gregkh=linuxfoundation.org@lists.openwall.com Authentication-Results: mx.google.com; dkim=fail header.i=@infradead.org header.s=bombadil.20170209 header.b=che3nTqo; spf=pass (google.com: domain of kernel-hardening-return-11656-gregkh=linuxfoundation.org@lists.openwall.com designates 195.42.179.200 as permitted sender) smtp.mailfrom=kernel-hardening-return-11656-gregkh=linuxfoundation.org@lists.openwall.com Mailing-List: contact kernel-hardening-help@lists.openwall.com; run by ezmlm List-Post: List-Help: List-Unsubscribe: List-Subscribe: Date: Wed, 7 Feb 2018 20:06:55 -0800 From: Matthew Wilcox To: "Tobin C. Harding" Cc: linux-mm@kvack.org, kernel-hardening@lists.openwall.com, linux-kernel@vger.kernel.org, "Kirill A. Shutemov" Subject: Re: [RFC] Warn the user when they could overflow mapcount Message-ID: <20180208040655.GD14918@bombadil.infradead.org> References: <20180208021112.GB14918@bombadil.infradead.org> <20180208031804.GD3304@eros> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180208031804.GD3304@eros> User-Agent: Mutt/1.9.1 (2017-09-22) X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: =?utf-8?q?1591796976786547518?= X-GMAIL-MSGID: =?utf-8?q?1591804254179712103?= X-Mailing-List: linux-kernel@vger.kernel.org List-ID: On Thu, Feb 08, 2018 at 02:18:04PM +1100, Tobin C. Harding wrote: > > +++ b/Documentation/sysctl/vm.txt > > @@ -379,7 +379,8 @@ While most applications need less than a thousand maps, certain > > programs, particularly malloc debuggers, may consume lots of them, > > e.g., up to one or two maps per allocation. > > > > -The default value is 65536. > > +The default value is 65530. Increasing this value without decreasing > > +pid_max may allow a hostile user to corrupt kernel memory. > > Just checking - did you mean the final '0' on this value? That's what my laptop emits ... mm/mmap.c:int max_map_count __read_mostly = DEFAULT_MAX_MAP_COUNT; include/linux/mm.h:#define DEFAULT_MAX_MAP_COUNT (USHRT_MAX - MAPCOUNT_ELF_CORE_MARGIN) include/linux/mm.h:#define MAPCOUNT_ELF_CORE_MARGIN (5) should be the same value for everybody.