Re: [PATCH 6/6] btrfs-progs: extent-tree: Fix a by-one error in exclude_super_stripes()

[Qu Wenruo <quwenruo.btrfs@gmx.com>]

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On 2020/1/3 上午12:56, David Sterba wrote:
> On Wed, Dec 18, 2019 at 09:19:42AM +0800, Qu Wenruo wrote:
>> [BUG]
>> For certain btrfs images, a BUG_ON() can be triggered at open_ctree()
>> time:
>>   Opening filesystem to check...
>>   extent_io.c:158: insert_state: BUG_ON `end < start` triggered, value 1
>>   btrfs(+0x2de57)[0x560c4d7cfe57]
>>   btrfs(+0x2e210)[0x560c4d7d0210]
>>   btrfs(set_extent_bits+0x254)[0x560c4d7d0854]
>>   btrfs(exclude_super_stripes+0xbf)[0x560c4d7c65ff]
>>   btrfs(btrfs_read_block_groups+0x29d)[0x560c4d7c698d]
>>   btrfs(btrfs_setup_all_roots+0x3f3)[0x560c4d7c0b23]
>>   btrfs(+0x1ef53)[0x560c4d7c0f53]
>>   btrfs(open_ctree_fs_info+0x90)[0x560c4d7c11a0]
>>   btrfs(+0x6d3f9)[0x560c4d80f3f9]
>>   btrfs(main+0x94)[0x560c4d7b60c4]
>>   /usr/lib/libc.so.6(__libc_start_main+0xf3)[0x7fd189773ee3]
>>   btrfs(_start+0x2e)[0x560c4d7b635e]
>>
>> [CAUSE]
>> This is caused by passing @len == 0 to add_excluded_extent(), which
>> means one revsere mapped range is just out of the block group range,
>> normally means a by-one error.
>>
>> [FIX]
>> Fix the boundary check on the reserve mapped range against block group
>> range.
>> If a reverse mapped super block starts at the end of the block group, it
>> doesn't cover so we don't need to bother the case.
>>
>> Issue: #210
>> Signed-off-by: Qu Wenruo <wqu@suse.com>
>> ---
>>  extent-tree.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/extent-tree.c b/extent-tree.c
>> index 6288c8a3..7ba80375 100644
>> --- a/extent-tree.c
>> +++ b/extent-tree.c
>> @@ -3640,7 +3640,7 @@ int exclude_super_stripes(struct btrfs_fs_info *fs_info,
>>  		while (nr--) {
>>  			u64 start, len;
>>  
>> -			if (logical[nr] > cache->key.objectid +
>> +			if (logical[nr] >= cache->key.objectid +
>>  			    cache->key.offset)
> 
> Do we have the same problem in kernel? The code does ">".
> 
Oh, kernel looks to have the same problem.

Time to fix it.

Thanks,
Qu


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