Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932460AbbFPImX (ORCPT ); Tue, 16 Jun 2015 04:42:23 -0400 Received: from mail.kernel.org ([198.145.29.136]:54559 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932347AbbFPIli (ORCPT ); Tue, 16 Jun 2015 04:41:38 -0400 From: lizf@kernel.org To: stable@vger.kernel.org Cc: linux-kernel@vger.kernel.org, Roman Gushchin , Andrew Shewmaker , Rik van Riel , Konstantin Khlebnikov , Andrew Morton , Linus Torvalds , Zefan Li Subject: [PATCH 3.4 030/172] mm/mmap.c: fix arithmetic overflow in __vm_enough_memory() Date: Tue, 16 Jun 2015 16:34:44 +0800 Message-Id: <1434443826-4929-30-git-send-email-lizf@kernel.org> X-Mailer: git-send-email 1.9.1 In-Reply-To: <1434443587-4599-1-git-send-email-lizf@kernel.org> References: <1434443587-4599-1-git-send-email-lizf@kernel.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2188 Lines: 66 From: Roman Gushchin 3.4.108-rc1 review patch. If anyone has any objections, please let me know. ------------------ commit 5703b087dc8eaf47bfb399d6cf512d471beff405 upstream. 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. [akpm@linux-foundation.org: use min_t] Signed-off-by: Roman Gushchin Cc: Andrew Shewmaker Cc: Rik van Riel Cc: Konstantin Khlebnikov Reviewed-by: Michal Hocko Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds [lizf: Backported to 3.4: - adjust context - there's no variable reserve] Signed-off-by: Zefan Li --- mm/mmap.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/mmap.c b/mm/mmap.c index 208e70f..cb6456d 100644 --- a/mm/mmap.c +++ b/mm/mmap.c @@ -112,7 +112,7 @@ struct percpu_counter vm_committed_as ____cacheline_aligned_in_smp; */ int __vm_enough_memory(struct mm_struct *mm, long pages, int cap_sys_admin) { - unsigned long free, allowed; + long free, allowed; vm_acct_memory(pages); -- 1.9.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/