Re: [PATCH v3] bcachefs: fix shift oob in alloc_lru_idx_fragmentation

[Hongbo Li <lihongbo22@huawei.com>]

On 2024/10/22 12:05, Jeongjun Park wrote:
> 
> 
>> Hongbo Li <lihongbo22@huawei.com> wrote:
>>
>> 
>>
>>> On 2024/10/21 23:43, Jeongjun Park wrote:
>>> The size of a.data_type is set abnormally large, causing shift-out-of-bounds.
>>> To fix this, we need to add validation on a.data_type in
>>> alloc_lru_idx_fragmentation().
>>> Reported-by: syzbot+7f45fa9805c40db3f108@syzkaller.appspotmail.com
>>> Fixes: 260af1562ec1 ("bcachefs: Kill alloc_v4.fragmentation_lru")
>>> Signed-off-by: Jeongjun Park <aha310510@gmail.com>
>>> ---
>>>   fs/bcachefs/alloc_background.h | 3 +++
>>>   1 file changed, 3 insertions(+)
>>> diff --git a/fs/bcachefs/alloc_background.h b/fs/bcachefs/alloc_background.h
>>> index f8e87c6721b1..163a67b97a40 100644
>>> --- a/fs/bcachefs/alloc_background.h
>>> +++ b/fs/bcachefs/alloc_background.h
>>> @@ -168,6 +168,9 @@ static inline bool data_type_movable(enum bch_data_type type)
>>>   static inline u64 alloc_lru_idx_fragmentation(struct bch_alloc_v4 a,
>>>                             struct bch_dev *ca)
>>>   {
>>> +    if (a.data_type >= BCH_DATA_NR)
>>> +        return 0;
>>> +
>>
>> oh, I found I have done the same thing in [1]("Re: [syzbot] [bcachefs?] UBSAN: shift-out-of-bounds in bch2_alloc_to_text"). But in my humble opinion, the validation changes also should be added. And in addition, move the condition about a.data_type into data_type_movable will be better. Just my personal opinion.:)
>>
>> [1] https://www.spinics.net/lists/kernel/msg5412619.html
> 
> I still disagree with the fix to make data_type_movable() do the validation,
> but I think [1] is definitely a patch that needs to be added.
> 
> However, [1] is far from preventing the shift oob vulnerability described
> in that syzbot report. Therefore, I think [1] should be written as a
> standalone patch and committed, rather than as a patch for that

I'm fine for this.:)

Thanks,
Hongbo

> syzbot report.
> 
>>
>> Thanks,
>> Hongbo
>>
>>>       if (!data_type_movable(a.data_type) ||
>>>           !bch2_bucket_sectors_fragmented(ca, a))
>>>           return 0;
>>> --