From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wi0-f176.google.com (mail-wi0-f176.google.com [209.85.212.176]) by kanga.kvack.org (Postfix) with ESMTP id D8DF76B006C for ; Tue, 3 Feb 2015 08:29:32 -0500 (EST) Received: by mail-wi0-f176.google.com with SMTP id bs8so24375752wib.3 for ; Tue, 03 Feb 2015 05:29:32 -0800 (PST) Received: from mx2.suse.de (cantor2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id jd3si2244893wic.15.2015.02.03.05.29.30 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Tue, 03 Feb 2015 05:29:30 -0800 (PST) Date: Tue, 3 Feb 2015 14:29:28 +0100 From: Michal Hocko Subject: Re: [PATCH] mm: fix arithmetic overflow in __vm_enough_memory() Message-ID: <20150203132928.GB8914@dhcp22.suse.cz> References: <1422536763-31325-1-git-send-email-klamm@yandex-team.ru> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1422536763-31325-1-git-send-email-klamm@yandex-team.ru> Sender: owner-linux-mm@kvack.org List-ID: To: Roman Gushchin Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton , Andrew Shewmaker , Rik van Riel , Konstantin Khlebnikov , stable@vger.kernel.org On Thu 29-01-15 16:06:03, Roman Gushchin wrote: > I noticed, that "allowed" can easily overflow by falling below 0, > because (total_vm / 32) can be larger than "allowed". The problem > occurs in OVERCOMMIT_NONE mode. s@OVERCOMMIT_NONE@OVERCOMMIT_NEVER@ > In this case, a huge allocation can success and overcommit the system > (despite OVERCOMMIT_NONE mode). All subsequent allocations will fall > (system-wide), so system become unusable. > > The problem was masked out by commit c9b1d0981fcc > ("mm: limit growth of 3% hardcoded other user reserve"), > but it's easy to reproduce it on older kernels: > 1) set overcommit_memory sysctl to 2 > 2) mmap() large file multiple times (with VM_SHARED flag) > 3) try to malloc() large amount of memory > > It also can be reproduced on newer kernels, but miss-configured > sysctl_user_reserve_kbytes is required. > > Fix this issue by switching to signed arithmetic here. > > Signed-off-by: Roman Gushchin > Cc: Andrew Morton > Cc: Andrew Shewmaker > Cc: Rik van Riel > Cc: Konstantin Khlebnikov > Cc: stable@vger.kernel.org With Andrew min -> min_t fixup Reviewed-by: Michal Hocko > --- > mm/mmap.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/mm/mmap.c b/mm/mmap.c > index 7f684d5..5aa8dfe 100644 > --- a/mm/mmap.c > +++ b/mm/mmap.c > @@ -152,7 +152,7 @@ EXPORT_SYMBOL_GPL(vm_memory_committed); > */ > int __vm_enough_memory(struct mm_struct *mm, long pages, int cap_sys_admin) > { > - unsigned long free, allowed, reserve; > + long free, allowed, reserve; > > VM_WARN_ONCE(percpu_counter_read(&vm_committed_as) < > -(s64)vm_committed_as_batch * num_online_cpus(), > @@ -220,7 +220,7 @@ int __vm_enough_memory(struct mm_struct *mm, long pages, int cap_sys_admin) > */ > if (mm) { > reserve = sysctl_user_reserve_kbytes >> (PAGE_SHIFT - 10); > - allowed -= min(mm->total_vm / 32, reserve); > + allowed -= min((long)mm->total_vm / 32, reserve); > } > > if (percpu_counter_read_positive(&vm_committed_as) < allowed) > -- > 2.1.0 > > -- > To unsubscribe, send a message with 'unsubscribe linux-mm' in > the body to majordomo@kvack.org. For more info on Linux MM, > see: http://www.linux-mm.org/ . > Don't email: email@kvack.org -- Michal Hocko SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org