Re: [PATCH] ocfs2: fix use-after-free when unmounting read-only filesystem

From: Luís Henriques
Date: Mon May 22 2023 - 09:22:48 EST

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Heming Zhao <heming.zhao@xxxxxxxx> writes:

> On Mon, May 22, 2023 at 01:23:07PM +0100, Luís Henriques wrote:
>> Joseph Qi <joseph.qi@xxxxxxxxxxxxxxxxx> writes:
>>
>> > On 5/22/23 6:25 PM, Luís Henriques wrote:
>> >> It's trivial to trigger a use-after-free bug in the ocfs2 quotas code using
>> >> fstest generic/452. After mounting a filesystem as read-only, quotas are
>> >
>> > generic/452 is for testing ext4 mounted with dax and ro.
>> > But ocfs2 doesn't support dax yet.
>>
>> Right, but I think it's still useful to run the 'generic' test-suite in a
>> filesystem. We can always find issues in the test itself or, in this
>> case, a bug in the filesystem.
>
> It looks you did some special steps for 452. In my env, without changing
> anything, I could pass this case successfully.

No, I haven't changed anything to the test. I just make sure there's a
scratch device to be used.

Maybe you can try to enable KASAN to catch the UAF. I've found the bug
without KASAN (i.e. I saw a NULL pointer panic), but enabling it also
detects the issue -- see below.

Cheers,
--
Luís

[ 91.928109] ==================================================================
[ 91.929519] BUG: KASAN: slab-use-after-free in timer_delete+0x54/0xc0
[ 91.930869] Read of size 8 at addr ffff8880389a8208 by task umount/669
[ 91.932533] CPU: 1 PID: 669 Comm: umount Not tainted 6.4.0-rc3 #236
[ 91.933807] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.0-0-gd239552c-rebuilt.opensuse.org 04/01/2014
[ 91.936158] Call Trace:
[ 91.936678] <TASK>
[ 91.937123] dump_stack_lvl+0x32/0x50
[ 91.937909] print_report+0xc5/0x5f0
[ 91.938685] ? _raw_spin_lock_irqsave+0x72/0xc0
[ 91.939642] ? __virt_addr_valid+0xac/0x130
[ 91.940534] ? __pfx__raw_spin_lock_irqsave+0x10/0x10
[ 91.941574] ? timer_delete+0x54/0xc0
[ 91.942357] kasan_report+0x9e/0xd0
[ 91.943110] ? timer_delete+0x54/0xc0
[ 91.943902] timer_delete+0x54/0xc0
[ 91.944643] ? __pfx_timer_delete+0x10/0x10
[ 91.945492] ? detach_if_pending+0x112/0x140
[ 91.946405] try_to_grab_pending+0x31/0x230
[ 91.947252] __cancel_work_timer+0x6c/0x270
[ 91.948102] ? __pfx___cancel_work_timer+0x10/0x10
[ 91.949073] ? try_to_grab_pending+0x31/0x230
[ 91.949956] ? __cancel_work+0xe3/0x130
[ 91.950746] ? mutex_unlock+0x6b/0xb0
[ 91.951485] ocfs2_disable_quotas.isra.0+0x3e/0xf0 [ocfs2]
[ 91.952635] ocfs2_dismount_volume+0xdd/0x450 [ocfs2]
[ 91.953676] ? __pfx___filemap_fdatawrite_range+0x10/0x10
[ 91.954757] ? __pfx_ocfs2_dismount_volume+0x10/0x10 [ocfs2]
[ 91.955898] ? filemap_check_errors+0x46/0xb0
[ 91.956737] generic_shutdown_super+0xaa/0x280
[ 91.957604] kill_block_super+0x46/0x70
[ 91.958415] deactivate_locked_super+0x4d/0xb0
[ 91.959861] cleanup_mnt+0x135/0x1f0
[ 91.960862] task_work_run+0xe3/0x140
[ 91.961887] ? __pfx_task_work_run+0x10/0x10
[ 91.962887] ? __x64_sys_umount+0xbb/0xd0
[ 91.963343] exit_to_user_mode_prepare+0xda/0xe0
[ 91.963867] syscall_exit_to_user_mode+0x1d/0x50
[ 91.964392] do_syscall_64+0x4f/0x90
[ 91.964800] entry_SYSCALL_64_after_hwframe+0x72/0xdc
[ 91.965387] RIP: 0033:0x7fa7664baacb
[ 91.965796] Code: fa 90 90 31 f6 e9 13 00 00 00 0f 1f 44 00 00 90 90 90 90 90 90 90 90 90 90 90 90 90 90 f3 0f 1e fa 90 90 b8 a6 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 058
[ 91.967851] RSP: 002b:00007ffc8d30da28 EFLAGS: 00000246 ORIG_RAX: 00000000000000a6
[ 91.968671] RAX: 0000000000000000 RBX: 00005628ef17a9c0 RCX: 00007fa7664baacb
[ 91.969464] RDX: 0000000000000000 RSI: 0000000000000000 RDI: 00005628ef17cdd0
[ 91.970253] RBP: 00005628ef17aad8 R08: 0000000000000073 R09: 0000000000000001
[ 91.971031] R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
[ 91.971790] R13: 00005628ef17cdd0 R14: 00005628ef17abf0 R15: 00007ffc8d310088
[ 91.972546] </TASK>

[ 91.972961] Allocated by task 632:
[ 91.973342] kasan_save_stack+0x1c/0x40
[ 91.973760] kasan_set_track+0x21/0x30
[ 91.974160] __kasan_kmalloc+0x8b/0x90
[ 91.974584] ocfs2_local_read_info+0xe3/0x9a0 [ocfs2]
[ 91.975168] dquot_load_quota_sb+0x34b/0x680
[ 91.975624] dquot_load_quota_inode+0xfe/0x1a0
[ 91.976092] ocfs2_enable_quotas+0x190/0x2f0 [ocfs2]
[ 91.976679] ocfs2_fill_super+0x14ef/0x2120 [ocfs2]
[ 91.977249] mount_bdev+0x1be/0x200
[ 91.977622] legacy_get_tree+0x6c/0xb0
[ 91.978014] vfs_get_tree+0x3e/0x110
[ 91.978415] path_mount+0xa90/0xe10
[ 91.978774] __x64_sys_mount+0x16f/0x1a0
[ 91.979171] do_syscall_64+0x43/0x90
[ 91.979537] entry_SYSCALL_64_after_hwframe+0x72/0xdc

[ 91.980213] Freed by task 650:
[ 91.980535] kasan_save_stack+0x1c/0x40
[ 91.980925] kasan_set_track+0x21/0x30
[ 91.981317] kasan_save_free_info+0x2a/0x50
[ 91.981744] __kasan_slab_free+0xf9/0x150
[ 91.982151] __kmem_cache_free+0x89/0x180
[ 91.982568] ocfs2_local_free_info+0x2ba/0x3f0 [ocfs2]
[ 91.983140] dquot_disable+0x35f/0xa70
[ 91.983509] ocfs2_susp_quotas.isra.0+0x159/0x1a0 [ocfs2]
[ 91.984096] ocfs2_remount+0x150/0x580 [ocfs2]
[ 91.984584] reconfigure_super+0x1a5/0x3a0
[ 91.984993] path_mount+0xc8a/0xe10
[ 91.985357] __x64_sys_mount+0x16f/0x1a0
[ 91.985750] do_syscall_64+0x43/0x90
[ 91.986125] entry_SYSCALL_64_after_hwframe+0x72/0xdc

[ 91.986799] The buggy address belongs to the object at ffff8880389a8000
which belongs to the cache kmalloc-1k of size 1024
[ 91.987965] The buggy address is located 520 bytes inside of
freed 1024-byte region [ffff8880389a8000, ffff8880389a8400)

[ 91.989287] The buggy address belongs to the physical page:
[ 91.989812] page:00000000bc93f4e4 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x389a8
[ 91.990719] head:00000000bc93f4e4 order:3 entire_mapcount:0 nr_pages_mapped:0 pincount:0
[ 91.991483] flags: 0x4000000000010200(slab|head|zone=1)
[ 91.991981] page_type: 0xffffffff()
[ 91.992321] raw: 4000000000010200 ffff888003041dc0 dead000000000100 dead000000000122
[ 91.993064] raw: 0000000000000000 0000000000100010 00000001ffffffff 0000000000000000
[ 91.993812] page dumped because: kasan: bad access detected

[ 91.994505] Memory state around the buggy address:
[ 91.994973] ffff8880389a8100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
[ 91.995656] ffff8880389a8180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
[ 91.996366] >ffff8880389a8200: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
[ 91.997050] ^
[ 91.997399] ffff8880389a8280: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
[ 91.998087] ffff8880389a8300: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
[ 91.998774] ==================================================================

Next message: Oliver Neukum: "Re: [syzbot] [fs?] [usb?] INFO: rcu detected stall in vfs_readlink"
Previous message: Arseniy Krasnov: "Re: [RFC PATCH v3 04/17] vsock/virtio: non-linear skb handling for tap"
In reply to: Heming Zhao: "Re: [PATCH] ocfs2: fix use-after-free when unmounting read-only filesystem"
Next in thread: Joseph Qi: "Re: [PATCH] ocfs2: fix use-after-free when unmounting read-only filesystem"
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