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

[Alan Huang]

On Oct 22, 2024, at 10:26, Hongbo Li <lihongbo22@xxxxxxxxxx> 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@xxxxxxxxxxxxxxxxxxxxxxxxx
>> Fixes: 260af1562ec1 ("bcachefs: Kill alloc_v4.fragmentation_lru")
>> Signed-off-by: Jeongjun Park <aha310510@xxxxxxxxx>
>> ---
>>  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

Your patch there is still triggering the issue.

> in my humble opinion, the validation changes also should be added. And in addition, move the condition about a.data_type into

There is already the validation:

bkey_fsck_err_on(alloc_data_type(a, a.data_type) != a.data_type

And the unknown data type is already printed in bch2_prt_data_type, additional validation doesn’t help much.

> data_type_movable will be better. Just my personal opinion.:)

In my personal opinion, I don’t think so :)

> 
> [1] https://www.spinics.net/lists/kernel/msg5412619.html
> 
> Thanks,
> Hongbo
> 
>>   if (!data_type_movable(a.data_type) ||
>>       !bch2_bucket_sectors_fragmented(ca, a))
>>   return 0;
>> --