From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from sunset.davemloft.net (unknown [74.93.104.97]) by ozlabs.org (Postfix) with ESMTP id 6D630DE015 for ; Thu, 17 Apr 2008 17:09:47 +1000 (EST) Date: Thu, 17 Apr 2008 00:09:46 -0700 (PDT) Message-Id: <20080417.000946.44234467.davem@davemloft.net> To: paulus@samba.org Subject: Re: [LMB][2/2] Restructure allocation loops to avoid unsigned underflow From: David Miller In-Reply-To: <18432.18107.854417.50018@cargo.ozlabs.ibm.com> References: <18432.18107.854417.50018@cargo.ozlabs.ibm.com> Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Cc: linuxppc-dev@ozlabs.org, linux-kernel@vger.kernel.org List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , From: Paul Mackerras Date: Sat, 12 Apr 2008 15:20:59 +1000 > There is a potential bug in __lmb_alloc_base where we subtract `size' > from the base address of a reserved region without checking whether > the subtraction could wrap around and produce a very large unsigned > value. In fact it probably isn't possible to hit the bug in practice > since it would only occur in the situation where we can't satisfy the > allocation request and there is a reserved region starting at 0. > > This fixes the potential bug by breaking out of the loop when we get > to the point where the base of the reserved region is less than the > size requested. This also restructures the loop to be a bit easier to > follow. > > The same logic got copied into lmb_alloc_nid_unreserved, so this makes > a similar change there. Here the bug is more likely to be hit because > the outer loop (in lmb_alloc_nid) goes through the memory regions in > increasing order rather than decreasing order as __lmb_alloc_base > does, and we are therefore more likely to hit the case where we are > testing against a reserved region with a base address of 0. > > Signed-off-by: Paul Mackerras This looks great, thanks for doing this work Paul. I'll try to find some cycles to validate these changes alongside the pending sparc64 NUMA changes I have.