Re: [PATCH] ocfs2: fix a null pointer derefrence in ocfs2_block_group_clear_bits()

[lishan]

ping ?
to Jan Kara

On 2020/3/12 10:38, lishan wrote:
> Hi, Jan Kara:
> 
> I have a long-standing problem,
> In the ocfs2 file system, there is a panic problem related to b_committed_data,
> details can be found in the historical mail.
> 
> Refer to the old version of the ext3 file system,
> ocfs2 file system uses the undo process to ensure that metadata
> which is not committed to disk is not reused.
> 
> I understand that for transactions that have not been committed,
> b_committed_data will not be NULL, so,
> in what scenario do you think b_committed_data will be set to NULL?
> 
> Thanks,
> Shan
> 
> On 2020/3/11 9:15, Joseph Qi wrote:
>>
>>
>> On 2020/3/9 16:26, lishan wrote:
>>> A NULL pointer panic dereference in ocfs2_block_group_clear_bits() happen again.
>>> The information of NULL pointer stack as follows:
>>>
>>> PID: 81866  TASK: ffffa07c3c21ae80  CPU: 66  COMMAND: "fallocate"
>>>   #0 [ffff0000b4d6b0b0] machine_kexec at ffff0000800a2954
>>>   #1 [ffff0000b4d6b110] __crash_kexec at ffff0000801bab34
>>>   #2 [ffff0000b4d6b2a0] panic at ffff0000800f02cc
>>>   #3 [ffff0000b4d6b380] die at ffff00008008f6ac
>>>   #4 [ffff0000b4d6b3d0] bug_handler at ffff00008008f744
>>>   #5 [ffff0000b4d6b400] brk_handler at ffff000080085d1c
>>>   #6 [ffff0000b4d6b420] do_debug_exception at ffff000080081194
>>>   #7 [ffff0000b4d6b630] el1_dbg at ffff00008008332c
>>>       PC: ffff00000190e9c0  [_ocfs2_free_suballoc_bits+1608]
>>>       LR: ffff00000190e990  [_ocfs2_free_suballoc_bits+1560]
>>>       SP: ffff0000b4d6b640  PSTATE: 60400009
>>>      X29: ffff0000b4d6b650  X28: 0000000000000000  X27: 00000000000052f3
>>>      X26: ffff807c511a9570  X25: ffff807ca0054000  X24: 00000000000052f2
>>>      X23: 0000000000000001  X22: ffff807c7cde7a90  X21: ffff0000811d9000
>>>      X20: ffff807c5e7d2000  X19: ffff00000190c768  X18: 0000000000000000
>>>      X17: 0000000000000000  X16: ffff000080a032f0  X15: 0000000000000000
>>>      X14: ffffffffffffffff  X13: fffffffffffffff7  X12: ffffffffffffffff
>>>      X11: 0000000000000038  X10: 0101010101010101   X9: ffffffffffffffff
>>>       X8: 7f7f7f7f7f7f7f7f   X7: 0000000000000000   X6: 0000000000000080
>>>       X5: 0000000000000000   X4: 0000000000000002   X3: ffff00000199f390
>>>       X2: a603c08321456e00   X1: ffff807c7cde7a90   X0: 0000000000000000
>>>   #8 [ffff0000b4d6b650] _ocfs2_free_suballoc_bits at ffff00000190e9bc [ocfs2]
>>>   #9 [ffff0000b4d6b710] _ocfs2_free_clusters at ffff0000019110d4 [ocfs2]
>>>  #10 [ffff0000b4d6b790] ocfs2_free_clusters at ffff000001913e94 [ocfs2]
>>>  #11 [ffff0000b4d6b7d0] __ocfs2_flush_truncate_log at ffff0000018b5294 [ocfs2]
>>>  #12 [ffff0000b4d6b8a0] ocfs2_remove_btree_range at ffff0000018bb34c [ocfs2]
>>>  #13 [ffff0000b4d6b960] ocfs2_commit_truncate at ffff0000018bc76c [ocfs2]
>>>  #14 [ffff0000b4d6ba60] ocfs2_wipe_inode at ffff0000018e57bc [ocfs2]
>>>  #15 [ffff0000b4d6bb00] ocfs2_evict_inode at ffff0000018e5db8 [ocfs2]
>>>  #16 [ffff0000b4d6bb70] evict at ffff000080365040
>>>  #17 [ffff0000b4d6bba0] iput at ffff0000803655d8
>>>  #18 [ffff0000b4d6bbe0] ocfs2_dentry_iput at ffff0000018c60a0 [ocfs2]
>>>  #19 [ffff0000b4d6bc30] dentry_unlink_inode at ffff00008035ef58
>>>  #20 [ffff0000b4d6bc50] __dentry_kill at ffff000080360384
>>>  #21 [ffff0000b4d6bc80] dentry_kill at ffff000080360670
>>>  #22 [ffff0000b4d6bcb0] dput at ffff00008036093c
>>>  #23 [ffff0000b4d6bcf0] __fput at ffff000080343930
>>>  #24 [ffff0000b4d6bd40] ____fput at ffff000080343aac
>>>  #25 [ffff0000b4d6bd60] task_work_run at ffff0000801172fc
>>>
>>> The direct panic reason is that bh2jh (group_bh)-> b_committed_data is null.
>>> It is presumed that the network was disconnected during the write process,
>>> causing the transaction abort. as follows:
>>> jbd2_journal_abort
>>>   .......
>>>   jbd2_journal_commit_transaction
>>>     jh->b_committed_data = NULL;
>>>
>>> _ocfs2_free_suballoc_bits
>>>   ocfs2_block_group_clear_bits
>>>     // undo_bg is now set to null
>>>     BUG_ON(!undo_bg);
>>>
>>> When applying for free space, if b_committed_data is null,
>>> it will be directly occupied, as follows:
>>> ocfs2_cluster_group_search
>>>   ocfs2_block_group_find_clear_bits
>>>     ocfs2_test_bg_bit_allocatable:
>>>       bg = (struct ocfs2_group_desc *) bh2jh(bg_bh)->b_committed_data;
>>>       if (bg)
>>>         ret = !ocfs2_test_bit(nr, (unsigned long *)bg->bg_bitmap);
>>>       else
>>>         ret = 1;
>>> b_committed_data is an intermediate state backup for bitmap transaction commits,
>>> newly applied space can overwrite previous dirty data,
>>> so, I think, while free clusters, if b_committed_data is null, ignore it.
>>> Host panic directly, too violent.
>>>
>>> Signed-off-by: Shan Li <lishan24@xxxxxxxxxx>
>>> Reviewed-by: Jun Piao <piaojun@xxxxxxxxxx>
>>> ---
>>>  fs/ocfs2/suballoc.c | 9 +++++++--
>>>  1 file changed, 7 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/fs/ocfs2/suballoc.c b/fs/ocfs2/suballoc.c
>>> index 939df99d2dec..aaf1b3cbd984 100644
>>> --- a/fs/ocfs2/suballoc.c
>>> +++ b/fs/ocfs2/suballoc.c
>>> @@ -2412,14 +2412,19 @@ static int ocfs2_block_group_clear_bits(handle_t *handle,
>>>  	if (undo_fn) {
>>>  		spin_lock(&jh->b_state_lock);
>>>  		undo_bg = (struct ocfs2_group_desc *) jh->b_committed_data;
>>> -		BUG_ON(!undo_bg);
>>> +		if (!undo_bg)
>>> +			mlog(ML_NOTICE, "%s: group descriptor # %llu (device %s) journal "
>>> +					"b_committed_data had been cleared.\n",
>>> +					OCFS2_SB(alloc_inode->i_sb)->uuid_str,
>>> +					(unsigned long long)le64_to_cpu(bg->bg_blkno),
>>> +					alloc_inode->i_sb->s_id);
>>
>> Seems a kind of workaround.
>> I am worrying about other abnormal cases of NULL b_committed_data, it
>> may lead to a corrupt filesystem.
>> So how about isolating the journal abort case?
>>
>> Thanks,
>> Joseph
>>
>>>  	}
>>>
>>>  	tmp = num_bits;
>>>  	while(tmp--) {
>>>  		ocfs2_clear_bit((bit_off + tmp),
>>>  				(unsigned long *) bg->bg_bitmap);
>>> -		if (undo_fn)
>>> +		if (undo_fn && undo_bg)
>>>  			undo_fn(bit_off + tmp,
>>>  				(unsigned long *) undo_bg->bg_bitmap);
>>>  	}
>>>
>>
>> .
>>