Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932418AbbFPImJ (ORCPT ); Tue, 16 Jun 2015 04:42:09 -0400 Received: from mail.kernel.org ([198.145.29.136]:54579 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932352AbbFPIlk (ORCPT ); Tue, 16 Jun 2015 04:41:40 -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 3.4 031/172] mm/nommu.c: fix arithmetic overflow in __vm_enough_memory() Date: Tue, 16 Jun 2015 16:34:45 +0800 Message-Id: <1434443826-4929-31-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: 2080 Lines: 64 From: Roman Gushchin 3.4.108-rc1 review patch. If anyone has any objections, please let me know. ------------------ commit 8138a67a5557ffea3a21dfd6f037842d4e748513 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. Signed-off-by: Roman Gushchin Cc: Andrew Shewmaker Cc: Rik van Riel Cc: Konstantin Khlebnikov 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/nommu.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/nommu.c b/mm/nommu.c index d3afb47..3f282f9 100644 --- a/mm/nommu.c +++ b/mm/nommu.c @@ -1916,7 +1916,7 @@ EXPORT_SYMBOL(unmap_mapping_range); */ 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/