From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-lb0-f170.google.com (mail-lb0-f170.google.com [209.85.217.170]) by kanga.kvack.org (Postfix) with ESMTP id C179D6B0038 for ; Thu, 29 Jan 2015 08:06:30 -0500 (EST) Received: by mail-lb0-f170.google.com with SMTP id w7so27780300lbi.1 for ; Thu, 29 Jan 2015 05:06:30 -0800 (PST) Received: from forward-corp1f.mail.yandex.net (forward-corp1f.mail.yandex.net. [95.108.130.40]) by mx.google.com with ESMTPS id u2si7305465lae.110.2015.01.29.05.06.28 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 29 Jan 2015 05:06:28 -0800 (PST) From: Roman Gushchin Subject: [PATCH] mm: fix arithmetic overflow in __vm_enough_memory() Date: Thu, 29 Jan 2015 16:06:03 +0300 Message-Id: <1422536763-31325-1-git-send-email-klamm@yandex-team.ru> Sender: owner-linux-mm@kvack.org List-ID: To: linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org, Roman Gushchin , Andrew Morton , Andrew Shewmaker , Rik van Riel , Konstantin Khlebnikov , stable@vger.kernel.org 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. 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 --- 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