Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755213AbZITRzZ (ORCPT ); Sun, 20 Sep 2009 13:55:25 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755018AbZITRzZ (ORCPT ); Sun, 20 Sep 2009 13:55:25 -0400 Received: from courier.cs.helsinki.fi ([128.214.9.1]:47626 "EHLO mail.cs.helsinki.fi" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754197AbZITRzY (ORCPT ); Sun, 20 Sep 2009 13:55:24 -0400 Date: Sun, 20 Sep 2009 20:55:20 +0300 (EEST) From: Pekka J Enberg To: Vegard Nossum cc: Ingo Molnar , linux-kernel@vger.kernel.org, Eric Paris , hugh.dickins@tiscali.co.uk Subject: Re: shmem_fill_super(): WARNING: kmemcheck: Caught 32-bit read from uninitialized memory In-Reply-To: <19f34abd0909201035t3157948amee532a3a5e96dbab@mail.gmail.com> Message-ID: References: <20090915080953.GA24958@elte.hu> <20090920072210.GA23787@elte.hu> <19f34abd0909201035t3157948amee532a3a5e96dbab@mail.gmail.com> User-Agent: Alpine 2.00 (DEB 1167 2008-08-23) Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4667 Lines: 115 On Sun, 20 Sep 2009, Vegard Nossum wrote: > Thanks for the report. > > AFAICT it's this line of mm/shmem.c: > > 2356 inode = shmem_get_inode(sb, S_IFDIR | sbinfo->mode, 0, > VM_NORESERVE ); > > and the loading of sbinfo->mode. It fits with the offset 0x3c(%esi) == > the address reported by kmemcheck and the offset of ->mode: > > (gdb) p &((struct shmem_sb_info *) 0).mode > $1 = (mode_t *) 0x3c > > Looking for the definition of mode_t, it seems to be defined in x86 > sources as unsigned short: > > arch/x86/include/asm/posix_types_32.h:11:typedef unsigned short __kernel_mode_t; > include/linux/types.h:typedef __kernel_mode_t mode_t; > > And the load was clearly 32-bit (kmemcheck said so) and in my assembly > dump it is also so. > > As I said before, I really don't like the solution of sprinkling the > kmemcheck annotations all over the place to cover up field padding > inside structs, not in the least because they confuse more than they > help, and they are not maintainable -- when somebody changes the > struct definitions, anything may happen to the field layout, and then > the annotation may have to change too. And it's not exactly obvious. > > I still vote for patching gcc as the long-term solution. There is > -fmudflap, there is -fstack-protector, why not a -fsacred-padding? Of > course it has to be implemented too... As Ingo already explained, we would need to wait for a year or so for "-fscared-padding" to appear in a GCC release and probably one year more for it to be picked up by distributions. So while we wait for such a thing to appear, how about something like this? Pekka >From a7cb569beb2d2fe769d558d1a017b6f5aa05d7eb Mon Sep 17 00:00:00 2001 From: Pekka Enberg Date: Sun, 20 Sep 2009 20:43:35 +0300 Subject: [PATCH] shmem: initialize struct shmem_sb_info to zero Fixes the following kmemcheck false positive: [ 0.337000] Total of 1 processors activated (3088.38 BogoMIPS). [ 0.352000] CPU0 attaching NULL sched-domain. [ 0.360000] WARNING: kmemcheck: Caught 32-bit read from uninitialized memory (9f8020fc) [ 0.361000] a44240820000000041f6998100000000000000000000000000000000ff030000 [ 0.368000] i i i i i i i i i i i i i i i i u u u u i i i i i i i i i i u u [ 0.375000] ^ [ 0.376000] [ 0.377000] Pid: 9, comm: khelper Not tainted (2.6.31-tip #206) P4DC6 [ 0.378000] EIP: 0060:[<810a3a95>] EFLAGS: 00010246 CPU: 0 [ 0.379000] EIP is at shmem_fill_super+0xb5/0x120 [ 0.380000] EAX: 00000000 EBX: 9f845400 ECX: 824042a4 EDX: 8199f641 [ 0.381000] ESI: 9f8020c0 EDI: 9f845400 EBP: 9f81af68 ESP: 81cd6eec [ 0.382000] DS: 007b ES: 007b FS: 00d8 GS: 0000 SS: 0068 [ 0.383000] CR0: 8005003b CR2: 9f806200 CR3: 01ccd000 CR4: 000006d0 [ 0.384000] DR0: 00000000 DR1: 00000000 DR2: 00000000 DR3: 00000000 [ 0.385000] DR6: ffff4ff0 DR7: 00000400 [ 0.386000] [<810c25fc>] get_sb_nodev+0x3c/0x80 [ 0.388000] [<810a3514>] shmem_get_sb+0x14/0x20 [ 0.390000] [<810c207f>] vfs_kern_mount+0x4f/0x120 [ 0.392000] [<81b2849e>] init_tmpfs+0x7e/0xb0 [ 0.394000] [<81b11597>] do_basic_setup+0x17/0x30 [ 0.396000] [<81b11907>] kernel_init+0x57/0xa0 [ 0.398000] [<810039b7>] kernel_thread_helper+0x7/0x10 [ 0.400000] [] 0xffffffff [ 0.402000] khelper used greatest stack depth: 2820 bytes left [ 0.407000] calling init_mmap_min_addr+0x0/0x10 @ 1 [ 0.408000] initcall init_mmap_min_addr+0x0/0x10 returned 0 after 0 usecs Reported-by: Ingo Molnar Signed-off-by: Pekka Enberg --- mm/shmem.c | 5 +---- 1 files changed, 1 insertions(+), 4 deletions(-) diff --git a/mm/shmem.c b/mm/shmem.c index d713239..a8f54f3 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -2307,17 +2307,14 @@ static int shmem_fill_super(struct super_block *sb, int err = -ENOMEM; /* Round up to L1_CACHE_BYTES to resist false sharing */ - sbinfo = kmalloc(max((int)sizeof(struct shmem_sb_info), + sbinfo = kzalloc(max((int)sizeof(struct shmem_sb_info), L1_CACHE_BYTES), GFP_KERNEL); if (!sbinfo) return -ENOMEM; - sbinfo->max_blocks = 0; - sbinfo->max_inodes = 0; sbinfo->mode = S_IRWXUGO | S_ISVTX; sbinfo->uid = current_fsuid(); sbinfo->gid = current_fsgid(); - sbinfo->mpol = NULL; sb->s_fs_info = sbinfo; #ifdef CONFIG_TMPFS -- 1.5.6.4 -- 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/