Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760148AbZCaNcx (ORCPT ); Tue, 31 Mar 2009 09:32:53 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1759979AbZCaNcj (ORCPT ); Tue, 31 Mar 2009 09:32:39 -0400 Received: from mtagate7.de.ibm.com ([195.212.29.156]:62048 "EHLO mtagate7.de.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759648AbZCaNch (ORCPT ); Tue, 31 Mar 2009 09:32:37 -0400 Date: Tue, 31 Mar 2009 15:32:23 +0200 From: Martin Schwidefsky To: linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: Carsten Otte , Nick Piggin , Jared Hulbert , Andrew Morton Subject: [PATCH] do_xip_mapping_read: fix length calculation Message-ID: <20090331153223.74b177bd@skybase> Organization: IBM Corporation X-Mailer: Claws Mail 3.7.1 (GTK+ 2.14.7; i486-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2456 Lines: 62 From: Martin Schwidefsky The calculation of the value nr in do_xip_mapping_read is incorrect. If the copy required more than one iteration in the do while loop the copies variable will be non-zero. The maximum length that may be passed to the call to copy_to_user(buf+copied, xip_mem+offset, nr) is len-copied but the check only compares against (nr > len). This bug is the cause for the heap corruption Carsten has been chasing for so long: *** glibc detected *** /bin/bash: free(): invalid next size (normal): 0x00000000800e39f0 *** ======= Backtrace: ========= /lib64/libc.so.6[0x200000b9b44] /lib64/libc.so.6(cfree+0x8e)[0x200000bdade] /bin/bash(free_buffered_stream+0x32)[0x80050e4e] /bin/bash(close_buffered_stream+0x1c)[0x80050ea4] /bin/bash(unset_bash_input+0x2a)[0x8001c366] /bin/bash(make_child+0x1d4)[0x8004115c] /bin/bash[0x8002fc3c] /bin/bash(execute_command_internal+0x656)[0x8003048e] /bin/bash(execute_command+0x5e)[0x80031e1e] /bin/bash(execute_command_internal+0x79a)[0x800305d2] /bin/bash(execute_command+0x5e)[0x80031e1e] /bin/bash(reader_loop+0x270)[0x8001efe0] /bin/bash(main+0x1328)[0x8001e960] /lib64/libc.so.6(__libc_start_main+0x100)[0x200000592a8] /bin/bash(clearerr+0x5e)[0x8001c092] With this bug fix the commit 0e4a9b59282914fe057ab17027f55123964bc2e2 "ext2/xip: refuse to change xip flag during remount with busy inodes" can be removed again. Cc: Carsten Otte Cc: Nick Piggin Cc: Jared Hulbert Cc: Andrew Morton Signed-off-by: Martin Schwidefsky --- mm/filemap_xip.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff -urpN linux-2.6/mm/filemap_xip.c linux-2.6-patched/mm/filemap_xip.c --- linux-2.6/mm/filemap_xip.c 2009-03-24 00:12:14.000000000 +0100 +++ linux-2.6-patched/mm/filemap_xip.c 2009-03-31 15:25:53.000000000 +0200 @@ -89,8 +89,8 @@ do_xip_mapping_read(struct address_space } } nr = nr - offset; - if (nr > len) - nr = len; + if (nr > len - copied) + nr = len - copied; error = mapping->a_ops->get_xip_mem(mapping, index, 0, &xip_mem, &xip_pfn); -- 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/