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Message-ID: <s5h1tt2sx94.wl%tiwai@suse.de> Date: Wed, 30 Jul 2014 17:05:11 +0200 From: Takashi Iwai <tiwai@...e.de> To: Josef Bacik <jbacik@...com> Cc: Chris Mason <clm@...com>, <linux-btrfs@...r.kernel.org>, <linux-kernel@...r.kernel.org> Subject: Re: [PATCH] Btrfs: Fix memory corruption by ulist_add_merge() on 32bit arch At Wed, 30 Jul 2014 17:01:52 +0200, Takashi Iwai wrote: > > At Wed, 30 Jul 2014 10:29:46 -0400, > Josef Bacik wrote: > > > > 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: [<f9234590>] 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:[<f9234590>] 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: > > >>>>> [<f923564d>] __btrfs_find_all_roots+0x9d/0xf0 [btrfs] > > >>>>> [<f9237bb1>] btrfs_qgroup_rescan_worker+0x401/0x760 [btrfs] > > >>>>> [<f9206148>] normal_work_helper+0xc8/0x270 [btrfs] > > >>>>> [<c025e38b>] process_one_work+0x11b/0x390 > > >>>>> [<c025eea1>] worker_thread+0x101/0x340 > > >>>>> [<c026432b>] kthread+0x9b/0xb0 > > >>>>> [<c0712a71>] ret_from_kernel_thread+0x21/0x30 > > >>>>> [<c0264290>] 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: <stable@...r.kernel.org> [v3.11+] > > >>>>> Signed-off-by: Takashi Iwai <tiwai@...e.de> > > >>>>> --- > > >>>>> > > >>>>> 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, > > You must do care as a maintainer. It's a long-standing and serious > bug since 3.11. The kernel hangs up immediately when you enable quota > on 32bit kernel. And it's really hard to revert it when the rootfs is > btrfs. (The mount follows the immediate hang up after reboot.) > > > since we're using pointers > > everywhere just change it to void * and be done with it. Thanks, > > Fix it quickly, then do cleanup. This is the golden rule for > regression :) Also, another question is whether you guys are OK to change the type to a pointer. Through a glance, the ulist code was intended to handle any generic data, thus it uses u64, right? Using void pointer breaks this concept. Takashi -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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