Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752055AbaG1JoY (ORCPT ); Mon, 28 Jul 2014 05:44:24 -0400 Received: from cn.fujitsu.com ([59.151.112.132]:20978 "EHLO heian.cn.fujitsu.com" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S1751458AbaG1JoW (ORCPT ); Mon, 28 Jul 2014 05:44:22 -0400 X-IronPort-AV: E=Sophos;i="5.00,978,1396972800"; d="scan'208";a="33860281" Message-ID: <53D61A2C.40805@cn.fujitsu.com> Date: Mon, 28 Jul 2014 17:38:52 +0800 From: Wang Shilong User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.1.0 MIME-Version: 1.0 To: Takashi Iwai , Chris Mason CC: Josef Bacik , , Subject: Re: [PATCH] Btrfs: Fix memory corruption by ulist_add_merge() on 32bit arch References: <1406537824-2376-1-git-send-email-tiwai@suse.de> In-Reply-To: <1406537824-2376-1-git-send-email-tiwai@suse.de> Content-Type: text/plain; charset="ISO-8859-1"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [10.167.226.245] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Takashi, This seems like a promising fix, i just have a little question: ulist_add() logic is we firstly cast a pointer to u64(see ptr_to_u64()), and then cast u64 to pointer back(u64_to_ptr()). So normally, arg u64 is actually a pointer. If the below overflow happens, that means casting can change original value? Am i missing something here? Thanks, Wang On 07/28/2014 04:57 PM, 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://bugzilla.novell.com/show_bug.cgi?id=887046 > 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. > > fs/btrfs/backref.c | 11 +++++------ > fs/btrfs/ulist.h | 15 +++++++++++++++ > 2 files changed, 20 insertions(+), 6 deletions(-) > > diff --git a/fs/btrfs/backref.c b/fs/btrfs/backref.c > index e25564bfcb46..d7a24620a963 100644 > --- a/fs/btrfs/backref.c > +++ b/fs/btrfs/backref.c > @@ -276,9 +276,8 @@ static int add_all_parents(struct btrfs_root *root, struct btrfs_path *path, > } > if (ret > 0) > goto next; > - ret = ulist_add_merge(parents, eb->start, > - (uintptr_t)eie, > - (u64 *)&old, GFP_NOFS); > + ret = ulist_add_merge_ptr(parents, eb->start, > + eie, (void **)&old, GFP_NOFS); > if (ret < 0) > break; > if (!ret && extent_item_pos) { > @@ -1008,9 +1007,9 @@ again: > goto out; > ref->inode_list = eie; > } > - ret = ulist_add_merge(refs, ref->parent, > - (uintptr_t)ref->inode_list, > - (u64 *)&eie, GFP_NOFS); > + ret = ulist_add_merge_ptr(refs, ref->parent, > + ref->inode_list, > + (void **)&eie, GFP_NOFS); > if (ret < 0) > goto out; > if (!ret && extent_item_pos) { > diff --git a/fs/btrfs/ulist.h b/fs/btrfs/ulist.h > index 7f78cbf5cf41..695fc2bac680 100644 > --- a/fs/btrfs/ulist.h > +++ b/fs/btrfs/ulist.h > @@ -57,6 +57,21 @@ void ulist_free(struct ulist *ulist); > int ulist_add(struct ulist *ulist, u64 val, u64 aux, gfp_t gfp_mask); > int ulist_add_merge(struct ulist *ulist, u64 val, u64 aux, > u64 *old_aux, gfp_t gfp_mask); > + > +/* just like ulist_add_merge() but take a pointer for the aux data */ > +static inline int ulist_add_merge_ptr(struct ulist *ulist, u64 val, void *aux, > + void **old_aux, gfp_t gfp_mask) > +{ > +#if BITS_PER_LONG == 32 > + u64 old64 = (uintptr_t)*old_aux; > + int ret = ulist_add_merge(ulist, val, (uintptr_t)aux, &old64, gfp_mask); > + *old_aux = (void *)((uintptr_t)old64); > + return ret; > +#else > + return ulist_add_merge(ulist, val, (u64)aux, (u64 *)old_aux, gfp_mask) > +#endif > +} > + > struct ulist_node *ulist_next(struct ulist *ulist, > struct ulist_iterator *uiter); > -- 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/