From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0a-00082601.pphosted.com ([67.231.145.42]:55443 "EHLO mx0a-00082601.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752937AbaG3O3w (ORCPT ); Wed, 30 Jul 2014 10:29:52 -0400 Message-ID: <53D9015A.90001@fb.com> Date: Wed, 30 Jul 2014 10:29:46 -0400 From: Josef Bacik MIME-Version: 1.0 To: Takashi Iwai CC: Chris Mason , , Subject: Re: [PATCH] Btrfs: Fix memory corruption by ulist_add_merge() on 32bit arch References: <1406537824-2376-1-git-send-email-tiwai@suse.de> <53D64D40.80606@fb.com> In-Reply-To: Content-Type: text/plain; charset="ISO-8859-1"; format=flowed Sender: linux-btrfs-owner@vger.kernel.org List-ID: On 07/30/2014 05:57 AM, Takashi Iwai wrote: > At Mon, 28 Jul 2014 16:01:55 +0200, > Takashi Iwai wrote: >> >> At Mon, 28 Jul 2014 15:48:41 +0200, >> Takashi Iwai wrote: >>> >>> At Mon, 28 Jul 2014 09:16:48 -0400, >>> Josef Bacik wrote: >>>> >>>> On 07/28/2014 04:57 AM, Takashi Iwai wrote: >>>>> We've got bug reports that btrfs crashes when quota is enabled on >>>>> 32bit kernel, typically with the Oops like below: >>>>> BUG: unable to handle kernel NULL pointer dereference at 00000004 >>>>> IP: [] find_parent_nodes+0x360/0x1380 [btrfs] >>>>> *pde = 00000000 >>>>> Oops: 0000 [#1] SMP >>>>> CPU: 0 PID: 151 Comm: kworker/u8:2 Tainted: G S W 3.15.2-1.gd43d97e-default #1 >>>>> Workqueue: btrfs-qgroup-rescan normal_work_helper [btrfs] >>>>> task: f1478130 ti: f147c000 task.ti: f147c000 >>>>> EIP: 0060:[] EFLAGS: 00010213 CPU: 0 >>>>> EIP is at find_parent_nodes+0x360/0x1380 [btrfs] >>>>> EAX: f147dda8 EBX: f147ddb0 ECX: 00000011 EDX: 00000000 >>>>> ESI: 00000000 EDI: f147dda4 EBP: f147ddf8 ESP: f147dd38 >>>>> DS: 007b ES: 007b FS: 00d8 GS: 00e0 SS: 0068 >>>>> CR0: 8005003b CR2: 00000004 CR3: 00bf3000 CR4: 00000690 >>>>> Stack: >>>>> 00000000 00000000 f147dda4 00000050 00000001 00000000 00000001 00000050 >>>>> 00000001 00000000 d3059000 00000001 00000022 000000a8 00000000 00000000 >>>>> 00000000 000000a1 00000000 00000000 00000001 00000000 00000000 11800000 >>>>> Call Trace: >>>>> [] __btrfs_find_all_roots+0x9d/0xf0 [btrfs] >>>>> [] btrfs_qgroup_rescan_worker+0x401/0x760 [btrfs] >>>>> [] normal_work_helper+0xc8/0x270 [btrfs] >>>>> [] process_one_work+0x11b/0x390 >>>>> [] worker_thread+0x101/0x340 >>>>> [] kthread+0x9b/0xb0 >>>>> [] ret_from_kernel_thread+0x21/0x30 >>>>> [] kthread_create_on_node+0x110/0x110 >>>>> >>>>> This indicates a NULL corruption in prefs_delayed list. The further >>>>> investigation and bisection pointed that the call of ulist_add_merge() >>>>> results in the corruption. >>>>> >>>>> ulist_add_merge() takes u64 as aux and writes a 64bit value into >>>>> old_aux. The callers of this function in backref.c, however, pass a >>>>> pointer of a pointer to old_aux. That is, the function overwrites >>>>> 64bit value on 32bit pointer. This caused a NULL in the adjacent >>>>> variable, in this case, prefs_delayed. >>>>> >>>>> Here is a quick attempt to band-aid over this: a new function, >>>>> ulist_add_merge_ptr() is introduced to pass/store properly a pointer >>>>> value instead of u64. There are still ugly void ** cast remaining >>>>> in the callers because void ** cannot be taken implicitly. But, it's >>>>> safer than explicit cast to u64, anyway. >>>>> >>>>> Bugzilla: https://urldefense.proofpoint.com/v1/url?u=https://bugzilla.novell.com/show_bug.cgi?id%3D887046&k=ZVNjlDMF0FElm4dQtryO4A%3D%3D%0A&r=cKCbChRKsMpTX8ybrSkonQ%3D%3D%0A&m=m3qrbo6ngjqKO%2B7ofuwRfQflb9Cx%2FXrF8TKejkPjxfA%3D%0A&s=199a5b6f0ed181925e9ba2c1060fe20d1c8ad2831dd1d96cc7eddd2a343fa72b >>>>> Cc: [v3.11+] >>>>> Signed-off-by: Takashi Iwai >>>>> --- >>>>> >>>>> Alternatively, we can change the argument of aux and old_aux to a >>>>> pointer from u64, as backref.c is the only user of ulist_add_merge() >>>>> function. I'll cook up another patch if it's the preferred way. >>>>> >>>> >>>> Yeah lets just use a pointer and see how that works out. Thanks, >>> >>> Oops, I forgot that ulist_add() takes aux as u64 and it calling >>> ulist_add_merge() internally. So, we can't change the type blindly >>> there, unfortunately. >> >> Looking back at the code, it seems that all aux arguments passed to >> ulist_add() in qgroup.c are pointers, too. So, indeed, all aux values >> are pointers, so far, and it'd be even cleaner to replace all these >> from u64 to void *. >> >> But, such a replacement patch will become difficult for backporting to >> stable kernels (the bug existed since 3.11, at least). So IMO, we >> should put a smaller fix like my previous one, let it backported to >> stable kernels, and do more comprehensive replacements to pointer on >> its top. > > Ping. Could you guys take my original patch as is, or do you prefer > changing in a different way? If so, how? > I don't care how hard it is to backport to stable, since we're using pointers everywhere just change it to void * and be done with it. Thanks, Josef