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

Su Yue
2020-01-03T03:05:20Z

On 2020/1/3 8:42 AM, Qu Wenruo wrote:
>
>
> 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.
>

Gentle reminder to save your time.

I saw the '>' as in the kernel code and send a patch for it.
Then Nikolay pointed out that the patch is unnecessary[1].
The fuzz image is rejected to be mounted by tree-checker earlier.

Besides, a cleanup series[2] was sent by him.

[1]:
https://lore.kernel.org/linux-btrfs/24721dc8-8bda-a086-ff1a-31a0b21a02b4@suse.com/T/#m4cc5153d1645177e0f81f00c86e10dfb36015def
[2]: https://patchwork.kernel.org/project/linux-btrfs/list/?series=205103

> Time to fix it.
>
> Thanks,
> Qu
>