> Hongbo Li <[email protected]> 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: [email protected]
>> Fixes: 260af1562ec1 ("bcachefs: Kill alloc_v4.fragmentation_lru")
>> Signed-off-by: Jeongjun Park <[email protected]>
>> ---
>> 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
syzbot report.
>
> Thanks,
> Hongbo
>
>> if (!data_type_movable(a.data_type) ||
>> !bch2_bucket_sectors_fragmented(ca, a))
>> return 0;
>> --
